THE ARUP JOURNAL

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; in* Vol. 18 No. 2 July 1983 Contents For the 90m x 60m factory for Adamswear at Published by Nuneaton (Job 9195) our client instructed us Ove Arup Partnership 13 Filzroy Street. London W1P 6BO to prepare a performance specification so THEARUP that subcontractors could use either portal frames or trusses. The grid for the 60m width Editor: Peter Hoggett is two spans of 30m with a 6m spacing down Art Editor: Desmond Wyeth FSIAD the length of the building. The truss design Assistant Editor: David Brown JOURNAL proved the most economical. The structural steelwork industry: 2 Trusses were also used for a 20m span tank A review, production shop for Joseph Ash and Sons by R. Haryott (Job 9580) and also for an awkward re• Fire protection, 5 development of an existing site for Samuel by M. Law Heath and Sons (Job 8567) which required some operational areas to be kept in Towers and flare stacks, 9 production while the new building was by J. Tyrrell completed around them. The use of plated steelwork in 12 a tension leg platform design, Figs. 4-5 by N. Prescott Factory for Adamswear The Central Electricity Workshops 15 at Nuneaton Johannesburg, Fig. 6 by B. Williams Joseph Ash and Sons Multi-storey steel-framed 18 tank production shop buildings in South Africa, by C. McMillan Architects: for both projects: Harper Fairley Partnership Local reports summary, 21 by J. Hannon

Composite frame and 25 metal deck construction, by I. MacKenzie Precedent and intuition in design, 26 All the papers in this issue of by J. Roberts The Arup Journal have been taken from THE ARUP PARTNERSHIPS' Industrial building: 30 Structural Steelwork Seminar which was Report from Birmingham, held in London, 8-11 November 1982. by R. Greenwood and P. Handley

Front cover: Victorian steel-the Forth Railway Bridge (Photo: Eric de Mare) Fig. 7 Samuel Heath and Sons, Back cover: The Papal Cross, Phoenix Park. Dublin (Photo: Harry Sowden) redevelopment of existing site. Architects: Kineton Design Group/ Bateman Associates (2) That in the eyes of many specifiers, against concrete. In recent times, for a The structural contractors and clients, there are many period of more than 20 years until around obstacles to the use of steel. These range 1975, demand for steel products exceeded steelwork industry: from long memories regarding supply steelmaking capacity in most parts of the Schemes on the drawing board at this problems, lack of understanding of the world, and certainly in Europe. One gets the moment include a further project at Coventry A review scope for savings in time or material, to impression that the most lucrative markets of a 30m span where a welded angle truss difficulties which exist in obtaining good for the steelmakers were the ones that took will be used and a 64m x 45m building where Richard Haryott advice on steel design. the biggest volume of simple steels, namely portal frames of 15m span have proved most (3) That designing in steel can only be ship building, the motor industry and heavy suitable. successfully accomplished if the task is engineering generally, and as a result supply Conclusions seen as a part of the whole: that is to say the of steel in the form of sections and other To summarize, our recent experience has Introduction contract procedures, the fabric and finishes structural shapes was never adequate. shown: Delays in steel supplies were certainly seen My task is to paint a general picture of the in relation to the structure, speed of con• (1) Buildings must be adaptable for future as the rule, rather than the exception. structural steelwork industry today. struction, fire protection and so on must all planning and flexible for future extension. I am going to concentrate on the situation be part of the evaluation. This may sound Sometime around 1975 the world supplies (2) Roofs must be strong enough to carry concerning the role of steel in the market obvious, but in fact it seems to me that much scene changed. The steelmakers, or the adequate services. place, and in the main I will also be concen• of industry is not tackling the task as a politicians, or both, appeared to get it wrong. (3) Truss or Portal? We will usually trating on those aspects relating to the use whole. In the UK for example, a grand expansion of of structural steelwork in multi-storey examine both schemes but trusses more A key must be education. There is nothing steelmaking capacity had been made, taking often offer the best solution. frames, in one-off special structures where magic about designing steel, but the capacity for production of liquid steel to (4) Bolted or welded trusses? Shop-welded reinforced concrete is a successful or even standard of education and training must be something in the region of 30m. tonnes per with site-bolted joints for almost all projects. dominant competitor. improved if excellence and value for money annum, and at that with no real changes in trusses had to be replaced with new with the universal columns/universal beams Clearly the review is made through the eyes are to be attained. Arups should examine productivity. In Europe capacity increased, monopitch trusses. Parallel lattice girders booms ideal for carrying local bending and (5) Grade 43 or Grade 50 steel? Most of an Arup engineer who is based mainly in what their role should be. and the new steelmaking plants were were used with structural T booms to which the tubular bracings efficient as long struts. schemes have used Grade 43 only but we London. In the time available it is obviously Background market conditions opened up all over the developing world. This angle bracings could readily be welded on To allow for transportation the truss is to be must bear in mind that the same mill delivery not possible to refer to all the many Steel sections have been used in all at a time when the post-OPEC price alternate sides. site bolted with Grade 8.8 bolts. of four to six weeks is offered. We should shocks were slowly reducing world demand therefore look for out places where Grade 50 differences in circumstances worldwide, but construction for over 100 years and for many Another form of truss construction we use We are finding that Grade 8.8 bolts have and helping to bring about major recession. can be used to advantage such as heavy nevertheless it seems to me that there are years the materials held a predominant has universal column or beam booms with largely replaced HSFG on most jobs as they loads on 'short' spans and for certain many areas of common experience and position in bridgework and in major building Suddenly world demand for steel products tubular bracing. The example is a 30m span are easier to use on site. Particularly with bracings. interest. frames. Competition from concrete and fell far short of capacity. Steelmakers in the with warren bracing. overseas jobs we avoid having two bolts of One of the purposes is to propose to you the other materials gradually reduced its market USA are working at less than 40% of their This same principle has been used for the the same size but different grades. Some (6) Grade 4.6 or Grades 8.8 bolts? Almost following main points or themes: share, but nonetheless the industry as a capacity, and in Europe the average output is boiler house at Telford District General trusses for Africa (Job 8399) were all M16 bolts are Grade 4.6 but M20 and M24 (1) That market forces are now such that whole did not seem to run into a feeling of around 60% of capacity. In the UK the BSC is Hospital (Job 4623) of 16m span and 9m transported in containers as individual angle in Grade 8.8 are frequently used for major steelwork is once again a sensible and decline until comparatively recently. currently producing around 10m. tonnes, and high. The initial design for a portal frame members and completely site bolted. The structural connections. economic alternative in many of our 'main• Steelmakers worldwide found themselves in the private sector production brings the total was abandoned when 10 tonne coal hoppers M20 and M24 bolts were grade 8.8 with the (7) Bracing members angle, rod or square stream' structures in areas where concrete a sellers' market for a considerable period of to around 14m. tonnes - pretty much in line had to be carried from the roof and a full M16 bolts in grade 4.6 to avoid any possible hollow sections? All are used with the has perhaps been dominant for the past two time, even if parts of the market, such as the with the capacity/demand situation for the height walkway above the hoppers. The confusion on site and we try to follow this advantage taken of square hollow sections or three decades. construction industry, were losing a battle EEC as a whole. welded steel truss met these requirements procedure in the United Kingdom. for long slender bracings. Industrial building: Fig. 1 - -10 Employment in the EEC steel industry Report from W. Germany Fig. 2 Birmingham Potential UK steel production capacity against actual UK steel production

150 Robert Greenwood potential production - Peter Handley * • France 100 Introduction Italy Birmingham Office has been involved in a actual production large number of single storey industrial buildings. These have ranged from small Britain extensions of 200m2 for family-owned Black Country businesses to a 20,000m2 ware• -12 house at Coventry. Belgium

Planning -5 Our experience has emphasized the need for Holland good planning and realistic prices. Indus• Luxembourg trialists in the West Midlands want two basic features for their buildings-a strong floor Dec 78 Sept 82 lib 70 75 and a good roof that won't leak. percentage change Good planning means designing a building Fig. 1 Coventry Trading for its immediate use whilst ensuring that it Estate from the air. will hold its value in the market place. Architects: W.S. Hattrell Steelmakers have had to make a real effort designs, and designers were lost to other units, and are difficult to access. Information Planning also means carefully balancing the & Partners to be more productive, particularly in the UK disciplines. Lack of understanding and on such vital issues as corrosion protection, minimum cost of construction with the where overmanning was serious, and market provision for maintenance probably also fire, special materials, welding and so on is future waste of money if the facility fails to forces have ensured that steel prices are caused the pendulum to swing away from not gathered into one centre of excellence, now cheaper than they have been for a long steel. In recent years, acceptance of and in some cases the information can even be adaptable or flexible. Fig. 2 Coventry Trading time, in comparison to the main competition weathering steels and the publication of far be better obtained elsewhere. Apparently, for An adaptable building will accept re- Estate: structure after of concrete. Figures show the change in the simpler codes and rules have swung the example, better advice on corrosion in steel planning of storage or re-organizing of fire which led to last few years to be quite dramatic, no doubt pendulum back, as have problems being can be obtained from the non-ferrous metals production. A flexible building will cope with provision of new even to an artificial extent because of encountered in the life of concrete finishes. trade association than from the steel expansion or alteration. building 2 government subsidies of one kind or another. The 20,000m warehouse we designed at In multi-storey buildings the pendulum had industry! In any event, familiarity in the use Certainly in the USA and the main EEC Coventry Trading Estate (Job No. 6670) five started to swing against steel much earlier. of steel at all levels of the industry has countries, steel is being sold at a loss, but declined, and this is no small obstacle to its years ago has already been used by Talbot Fig. 3 Warehouse As for bridges, regulations of one kind or even if this changes, it still seems likely that wide use. This lack of familiarity affects not as a 'knock down' production line for Alexander Duckham another were a contribution in the process, overcapacity will keep prices down to make only knowledge of the material, and analysis exporting cars to Iran. It is now used as their and Co. Ltd. Architects: but mainly covering other problems such as steel more competitive than in recent years, of complex details, but also the setting up of national distribution centre. It can, if needed Harper, Fairley fire protection. In some parts of the world, and supply problems are unlikely to be as measurement, cost control, and contract in the future be sub-divided into a number of Partnership fire regulations are not very onerous, or difficult for some time to come. procedures to take full advantage of smaller units. perhaps not enforced, with the result that So for the first time in many years, we find steel frames do not have to carry the potential savings of time and material in ourselves in a position where price and Adequate provision must always be made for additional cost and time penalty of steel structures in those situations where it supply issues are such that steel is a service loads and some spare capacity is encasement in concrete, spray coatings or could and perhaps should be viable. material which must be considered more always desirable - but there is rarely any dry linings. In some countries such as the UK seriously, particularly as many clients or Design approach need to provide for production loads. it would be held that fire regulations are too purchasers of construction are far more It has been mentioned • before that the Equipment and material handling can severe, or perhaps unreasonably interpreted, actively demanding steel, and are examining market conditions for steel are such that it is always be supported on a separate adding unnecessarily to the cost of steel alternative design and contract arrange• now relatively cheaper and more readily structure. This was done at Coventry and structures. We probably can all quote ments to achieve better results. If we do not available than for some time. With the also at Aldridge when a high level barrel- examples of that, and certainly many of us more actively make steel one of our design pressures to construct more quickly (always filling operation had to be included. must have felt from time to time that more skills, we will be doing both ourselves and there but probably now stronger as a result research is needed to understand better Layout our clients a disservice. of high land values and the high cost of what happens to steel buildings in fires - Structural costs increase with the span Obstacles to the use of steel borrowing), we must be prepared to take not just isolated members making up chosen. For light industry and small product The material conditions mentioned advantage of steel frames in the right frames. In Ove Arup & Partners, we are in a storage, 15 to 30m stanchion spacing is previously are clearly not the only reasons circumstances. better position than many to seek and obtain suitable. Medium production and general why use of structural steels declined in good advice on this, and probably also in a We have seen that the steel as a material has warehousing usually require spans of 24 to many of the world markets. Price and supply better position than most to encourage new become more competitive against concrete 36m. Heavy industries and high/dense difficulties played their part, but many other approaches, development of cheaper mat• as a material, but it is also worth considering warehousing often need spans up to 50m. factors also were of great significance. erials, and a wider understanding of the what is happening to the 'finished' product. Even in fields of activity where steel is a Selected examples main issues. natural,-things can go wrong which change On simple structural frames, such as Aspects of design and detailing can be high• the economic or technical balance. As an At the same time that these supply, cost, sections used in straightforward multi• lighted by examples of Birmingham example we have only to think about the box legislative and other factors have helped storey frames, the fabricated and erected designed projects. girder bridge. After the Second World War a swing the pendulum away from steel, the cost of the steel is perhaps more than Alexander Duckham and Co. Ltd. at Aldridge massive bridge building effort had to be influence of research and graduate design double the cost of the raw material. Possibly (Job No. 6619) required a new warehouse and undertaken in Germany to replace the aids promoted by the competing concrete now the labour costs are increasing faster 42mm diameter rod in Grade 50 steel with was necessary to repair some of the main filling shop of about 6,000m2 area with a hundreds of major structures destroyed or industry pushed it even further. In the UK the than the material itself, but in any event they High strength friction grip bolt connections. valley girders and the best solution was clear height of 10m and with a flat roof. We damaged, and the elegant and economical Cement and Concrete Association has most represent the area of greatest fluctuation. If The entrance canopy edge beam is a 30m provided by the site welding of new angle were appointed as prime agents with total box girder steel bridge emerged as a domi• effectively promoted the use of concrete, fabrication is complex or difficult, then the span box girder. members. To stabilize the gable ends, props design responsibility for all aspects except nant solution. Some 10 years or so ago the runs training courses for specifiers, clients, finished product cost can increase of rectangular hollow sections were used. the plant. The building has a structural grid The former Armstrong Whitworth Aircraft position was changed by the series of operatives and so on, and is a place to which dramatically, in some cases reaching more of 15m x 12m and we designed warren Factory at Coventry is now Coventry Trading The replacement building is 260m long x 75m failures in box girders, partly brought about many people in the building industry would than seven times the cost of the raw braced welded angle trusses at 6m centres Estate. This is a very long building with a wide with internal stanchions on a 20mx15m by a lack of understanding of both material turn for advice, They are a semi-independent material. with Multibeams as purlins. Universal width of 110m, having two spans of 30m and grid. Although we normally find that welded and geometrical instability in the thin plates. organization financed by a levy on cement In this age of increasing accountability, and column stanchions were used internally but one of 40m, and the roof is of steel angle steel trusses are the most economical for The reasons were of course complex, but sales which produces them an income of more measurement of everything, we are as a 4-hour fire rating was required at walls, riveted construction. As the result of a major this size of grid, we used plastically nevertheless one of the results was a new around £5-6m. per annum. In contrast, the often under pressure to produce maximum the perimeter columns were of precast fire near the centre of the building, we were designed portal frames and valley beams set of design rules (quite understandably) nearest equivalent in the steel industry in the area for minimum material, under the concrete. The supports for the barrel loading appointed for two structural contracts. and the bracings were circular hollow imposed on designers, which for a while UK is Constrado, which is wholly financed by proposition that this will equate to minimum area served by conveyors required 40 beams Rather than rebuild on the same area the sections. The portal frames will allow easy tipped the balance of economy away from the BSC, and in the minds of many is simply cost. Clearly this is not always so, and the of 15m span and here it was most client decided to have new gable ends to the construction of sub-division walls for any box girders to plate girders and even to not able to cope in the same way on a budget greater use of material, if accompanied by economical to use castellated universal parts which were saved from the fire (Job future re-organization. concrete. For a while, in the UK and else• of less than £400,000 per annum. The centres less fabrication and greater simplicity, can beams. The building was fully braced with 6591) and then provide a new separate At Icknield Port Road, Birmingham (Job where, there was a dearth of steel bridge of research and information in the steel easily be shown to produce a more angles at roof level but the side bracing was buildinn 'Job 6670). For the two gable ends it 6669), a number of 18m span steeply pitched sector are scattered around manufacturing economical result. However, even in this we Lunokhod 1, which landed on the moon in need to be careful, as recent developments fabricators do not like quoting main contrac• entirely a steel solution, with lightweight The life cycle of the intuitive process: illustrated by the work of Labrouste in automated fabrication processes are in tors for steel sub-contracts, as they cannot steel or aluminium cladding. At one stage, 1970 looks like a traditional samovar. The part changing the scene, and are making be sure they are quoting to all the main for planning and other reasons, the rise of the corporate client has also brought seemingly more complex fabricated shapes contract tenderers, and are certain to incur claddings to a two-storey office block were with it new problems for the designer. The more economical through reduction in far greater tendering costs, which will of changed to brick, and the frame changed to principal of these is his inability to deal with weight. course have to be passed on to the clients. concrete, because the architect preferred the totality of the design problem. He now Complicated measurement is often em• detailing brick supported by concrete rather Again measurement methods and contract finds himself pari passu with the executive in ployed, even for very small works, and than by steel. This illustrates that con• procedures must be considered as part of a niche in his client's hierarchy. The very inequitable conditions of contract imposed siderable effort is needed to change that the design criteria. Constrado have recently essence of design is the need to transcend on the small man. Recent examples of this confidence factor, and also the obvious point (perhaps belatedly) published the result of artificially created boundaries. The threat of on a small steelwork sub-contract have pro• that, taken together, a decision for steel independent assessments on several case the corporate client is the precedence of his duced tender figures perhaps three times as cladding and steel frames seems 'right' studies which show steel-framed buildings own organization. Unless great care is taken, high as might be normal. By and large, this whereas the heavy cladding seems 'wrong'. to give very considerable savings in time an intuitive design approach can cause kind of difficulty does not apply to reinforced Why? over any reinforced concrete alternatives, ructions. We have not yet learned how best concrete work, and so we have to be careful • but much would depend on the contract The question of fire protection is fun• to relate to the large corporate organization to ensure that the right procedure be used if • procedures adopted, for it can very easily be damental. The addition of mineral fibre and yet still retain our ability to innovate. the overall aim is to be achieved. Fig. 11 shown that in many cases to achieve the sprays or dry claddings, etc., increases the Coda 1 and 2 Two new graduates from different univer• St. Genevieve Library 1843- banded savings in time, steelwork sub-contracts cost of the frame by more than 30% in the Derek summed up his talk in two thoughts: sities in the UK were interviewed recently to barrel vaults in stone replaced by have to be let before the main contract, UK, although this perhaps represents only (1) Most architects' work and most of our see if their courses were perhaps biased banded barrel vaults in cast iron committing the client to a process which he around 12% of the total cost of the (Photo: Architectural Association) work is concerned with buildings which lie in towards concrete, rather than steel, and it might not want. New forms of contract such structure, including floors. In the USA the scale between the house and the tower or was quite encouraging to discover that there as the JCT 80 in the UK are making increase is less because, presumably, there was no bias. Both left university equally in• bridge where the structure is dominant. At nominated sub-contracts less attractive to is far more competition in the fireproofing Fig. 12 experienced in the two materials. However, it this in-between scale, whether structure is clients, and there are vested interests which market. Within the fireproofing element, by Bibliotheque Nationale 1862-8 is plain, certainly in the UK, that from that expressed or not is a function of the make it harder for the consulting engineer to far the largest element is for treating the the arches which combine to support architect's personal morality of form. What stage forward familiarity with steel does not the domes give ornamentation from the overcome resistance to organizing contracts beams (70-75%) as opposed to the •am we find to day is a search for originality come easily. We have recently completed the geometry. The fluted cast iron columns in some other form to overcome this. In my columns. If we can do something to reduce where many of our luminaires cast light only design of a large and complex phar• remain inhibited by the tradition view this is something we must watch very the beam element, we may achieve on themselves, leaving principles in the dark. maceutical research laboratory, and this was of stone. (Photo: Rab Bennetts) carefully, particularly as there are signs that worthwhile savings. Lacking originality, there is an obedience to, but not a listening to the precedent. Misplaced precedent Remember Blake: 'we are led to believe in a Conclusions lie when we see with, not through, the eye'. There is much evidence to suggest that steel approach. There is nothing magic about The engineer for his part with his now very as a material is now relatively cheaper than designing in steel, but rather it is a simple powerful analytical tools - the new altars of it has been for some time, and is far more question of education and training. The our profession - is probably sacrificing his readily available. There is a growing demand industry has lost a considerable amount of intuition at an alarming pace, encouraged by from discerning clients and specifiers to experienced people over the years, and we the academics with which he spends the take account of this, and we should seize the must examine how we are going to fit into, or most formative years of his life. opportunity to promote its use in those even adapt to future needs. The characteristics sought today are those cases where we can gain advantage for our In designing in steel, we must not lose sight of performance, heat, light, sound, durability, clients. It could be quite a potent weapon in of the whole. This is true of any material, but Fig. 3 adaptability and so on. As we seek to specify our armoury. in the present state of the art, it is Hall 7, National Exhibition Centre them to define our places, we remove Birmingham: a successful use of There are, however, some obstacles in the particularly so for steel. We have seen how ourselves from the reality of the materials exposed structural steelwork way of the specifier and contractor in using contract matters, questions of measurement themselves. Architects: Edward D. Mills and Partners steel. Many of these should be quite easy to estimating, and speed of construction are all As we remove ourselves from the materials, (Photo: Ove Arup & Partners) reduce or even eliminate with the right major factors in the design process. we remove ourselves from the forms they take and thence from the development of Fig. 13 Fig. 14 any structural intuition. Northumbrian 1830 Emperor Hirohito of Japan (left) with (2) In the construction industry, new embellished with Stephenson's his chief of staff inspecting sound materials and their fabricated elements Corinthian fluting to the chimney detectors for locating enemy aircraft, Osaka 1934 replace or substitute for old materials. The form of the new copies the form of the old. Arch bridges in stone are replaced by arch Good stuff. Baker replied at the Edinburgh held, was of little value unless it was bridges in cast iron; cast iron baths by Literary Institute. He expressed doubts as to accompanied by practical experience, sound plastic baths in exactly the same form. whether Morris had the faintest knowledge judgement and bold initiative. In the St. Genevieve Library, 1843, Labrouste of the duties which the great structure had to Other protagonists of new technology were replaced banded barrel vaults in stone by perform. How then could he judge the tolerated more sympathetically. Perhaps the banded barrel vaults in cast iron. The details impression which it made upon those that forms were less outrageous even if of the arches clearly indicate they were could appreciate the direction of the lines of precedents were absent. Burton's cast' and the joints differentiate for us what stress and the fitness of the several greenhouse at Kew and Paxton's work at was made off-site from that connected on- members to resist the forces? Probably, Chatsworth and the results at the Crystal site. Baker went on, 'Mr. Morris would judge the Palace are testimony to this. Stephenson's At the time Labrouste designed the National beauty of a design from the same Britannia Bridge was much admired. (This Library in 1862-8, cheap puddled wrought standpoint, whether it was for a bridge a mile itself has been ruined by the intervention of iron was available. Here the arches which long or for a silver chimney ornament. It is an unsympathetic technological repair.) combine to support and define the domes impossible for anyone to pronounce A point had been reached where, for many have a completely different expression. The authoritatively without knowing its structures, the architecture was derived from parts are clearly rolled or hammered and functions. The marble columns of the the engineering. rivetted together. Process and engineering Parthenon are beautiful where they stand are evident with ornamentation from the but if we used it as a funnel for an Atlantic Without the development of architectural geometry of the parts and no cast foliage as liner, it would to my mind cease to be forms relevant to new technology, the in the first library. The column remains cast beautiful but of course Mr. Morris may think pendulum could swing even further from iron fluted and with an Ionic Capital - or otherwise'. precedent but also away from the intuition Baker recognized towards the god of one could say it remains inhibited, like all The dangers of new technology analytical methods. Shell Mex House, built 19th century columns, by the tradition of New technology could no longer be ignored in 1933, was described as architecture stone. by those supporting precedent, partly sacrificed on the altar of structural engineer• Reprise because technology had to be compre• ing, and the new wave of buildings as The theme dilemma - precedent v. intuition hended in order to attack it and partly Portland Stone quarries hung on steel - remains unresolved. But we are more self- because the technologists themselves were frames. aware. One wonders whether such self- not above abusing their new found talent. But even the epitome of advanced awareness is inhibiting. The next time you Benjamin Baker was very well aware of this. technology, the exploration of space, shows are detailing a concrete column to resemble His great dictum was that all theoretical us that the world of precendent remains alive the steel column the architect really wanted calculations involved assumptions that were and well, as comparison of Russian and if only the fire regulations permitted, will you often convenient rather than true; that they American man landing vehicles demon• be daunted? And will you be able to convince could be valuable as a check but disastrous strates. The Northrop Corporation 1966 lunar your peers of the wisdom of precedent and if accepted with blind faith. Technology, he vehicle is straight out of Disneyland. the need for intuition? 29 Intuition and the first iron frames: The skeletal frame The first iron frame buildings in England had expansion and reduction of Young's Steel structures and fire safety no real architectural precedents except in Fire protection modulus caused by increase of temperature There is no evidence to suggest that in the external walls and the entasis of the cast and/or temperature gradients in the section. buildings designed to modern standards of iron columns. Early examples are at Milford Margaret Law In fires larger deflections than normal can be construction, the structural material itself 1792-3, Shrewsbury 1796-7, Salford 1899-01, accepted, generally at least span/30. has an effect on the life risk, i.e. there is no Leeds 1802-3 and Belper 1803-4. Because of its high thermal conductivity, reason to believe that a person in a modern Introduction The use of iron spread to the external walls uniform temperatures are attained rapidly in steel-framed building is more likely to suffer as in Arkwright's Masson Mill, Cranford, In 1980, Ove Arup and Partners and CBLIA many steel sections. For a given rate of injury or death by fire than a person in a • (Centre Belge-Luxembourgeois d'lnforma- 1783, the cast iron Doric columns in heating, a heavy section will heat up more modern building of concrete, brick, wood or tion de I'Acier) completed a joint study of Hartley's Liverpool Dock, 1845, and the boat slowly than a light one; the massivity of the masonry construction. research into the behaviour of structural store at Sheerness, 1858-60. In each case, section (volume in relation to exposed Most major property losses in fires are those steel elements exposed to fire. The study however, elements of the iron construction surface area) has a significant effect on its in industrial buildings - warehouses and was financed by the European Coal and were constrained by precedents developed performance in fire. large production and storage areas - and it Steel Community (ECSC) with the purpose of rationally in other materials. is the loss or damage of the contents which identifying priorities for research in the field The metamorphosis of the column: makes up the main cost of the fire. The of fire safety of building construction. We The trabeated form of architecture (column Fig. 7 Fig. 8 causes of fire spread include such features interpreted the broad purpose of ECSC- as combustible materials on wall and roof and lintel) was derived for masonry Albert Dock buildings in Sheerness Boat Store Liverpool by Hartley 1848 by Col. Green 1858-60 funded research to be to increase the use of surfaces, delay in detection, lack of compart- construction by Greek intuition. The practice the Doric Columns are cast iron the frame emerges steel in building. We therefore tried to mentation and poor details at junctions of of shaping the columns to suit the identify not only obstacles to the use of steel compartments. There is no reason to believe perspective from which buildings were most but also circumstances favouring its use. that the use of steel construction is more frequently viewed and the decoration to the This note summarizes our findings and likely to lead to these major fire losses. column capitols and shafts became includes some later information. embodied in strict 'orders' which were Behaviour of steel in fire written down and illustrated. Thanks to As with other structural materials, the Fire protection of steel J3 Vitruvius, the rules were preserved so that by 3 mechanical properties (tensile strength, Properly designed steel construction can the time Europe had emerged into the yield strength and Young's modulus) give adequate fire resistance and in many Renaissance, there was an established decrease with temperature. Values have It situations subsequent repair, particularly for precedent for the appearance of columns. been codified for design? Mild steel, pro• mild steel, is a simple operation. In certain When masonry was replaced by a new 'MriFi,, vided it has not exceeded a temperature of circumstances very little fire resistance may material, cast iron, designers found it hard to • - 'MM. about 900°C, recovers most of its strength be needed, either because the potential fire break with convention. Hence Jesse op cooling. exposure can be demonstrated to be low or Hartley's cast iron columns at Liverpool because the steel can be sacrificed in the dock, already mentioned, although The heated steel element will fail when the event of fire without prejudice to the overall handsome, were stone look-alikes. And in yield stress decreases to the value of the fire safety objectives. the first iron-framed buildings, the cast-iron working stress. (This can alter with the Normally, it is necessary to design the columns remain constrained by precedent. formation of plastic hinges.) The steel elements so that the steel does not reach its temperature at this moment is defined as the The reason not to break convention is critical temperature within the fire resis• critical temperature. It depends essentially unclear. Possibly it was the fact that a tance period imposed by regulations. Regu• on the loading, the degree of restraint, the column is a plain affair as defined by lations take into account experience of end conditions, and the type of steel. It is function. The link that allowed the precedent building fires and, in a somewhat arbitrary therefore a mistake to define a single value, to be followed was the technology of timber way, the nature, height and use of the 540°C for example, for the critical - used as patterns by both masons and iron Fig. 9 Figs. 1-2 building. The periods of fire resistance speci• temperature of steel. founders. Guaranty Building, Buffalo, USA The Centre Pompidou, Paris. fied range from a half hour to two hours, or 1894-95, facade Before the element attains its critical tem• Architects: Piano & Rogers even four hours for certain locations deemed Not knowing how to deal with columnar perature, it can deform under the effects of (Photos: Ove Arup & Partners) to be particularly dangerous. elements seems to have persisted as a problem, for we find many otherwise Fig. 10 functional objects having classical embel• Shell Mex House 1933- Portland Stone lishments. Even Robert Stephenson quarries hung on steel frames as succumbed. In 1830, one of the locomotives architecture is sacrificed on the he designed, The Northumbrian, was put into altar of structural engineering service resplendent with a Corinthian fluted (Photo: Architectural Association) chimney. The designer's dilemma in defining an Meads Station, despite their theoretical strength particularly in tension. Adler and intuitive solution in cast iron was only rarely relevance to the hammer beam roof of the Sullivan are usually credited with designing solved elegantly. By 1874-75, Jabrouste was shed, give the edifice the air of a 'mere the buildings which are regarded as the first able to define an altruistic form for the cast caricature'; 'mock castellated work, shields modern steel frames - the Casson Building iron column in the second of his library without bearings, ugly mouldings, no- and the Pirie and Scott Building, both in buildings - the National Library. Gone is the meaning projections and all sorts of Chicago, and The Guaranty Building, Buffalo. ornamentation and the iron foliage. Instead unaccountable breaks .. . make up a design Engineers' architecture and more conflict the columns merge with the domes they at once costly and offensive and full of with precedent: support and the form expresses the pro• pretensions'. Clearly heresy must be Meanwhile engineers were finding other cesses of rolling and forging involved in their stamped out. Thus did the Christian novel applications for which no architectural manufacture. Only the shaft remains fluted Functionalist give his verdict on what was precedent existed. as a throw-back to earlier precedent. certainly 'engineers' architecture'. 1 As we shall see later the problem of the Between 1795 and 1803 Telford constructed The skyscraper is born column was more generally overcome the Pont Cysyllte aqueduct carrying the Notwithstanding such attempted divine because of two factors - firstly the need for Ellesmere canal over the River Dee near 1 interventions the use of metal frames pro• fire protection; secondly and more important Llangollen. The form of the iron trough gressed, if only slowly. By the middle of the the fact that concrete and steel had become spanning the masonry columns is simplicity 18th century, iron had been used in widely available by the 1890s and these did itself, echoing only the loads being resisted, commercial buildings on both sides of the not permit the easy copying of Greek order. and has no formal memories. Sir Walter Atlantic: Jamaica St., Glasgow and Oriel Scott called it: 'The greatest work of art he Chambers in Liverpool (whence the oriel Railways and the ecclesiologists hit back had ever seen' - praise indeed. Incidently window) and buildings by Bogardus and the The rapid development of the railway from the work of art was only produced after Badger in New York (including the Otis 1825 onwards gave engineers rather than Telford had successfully tried out the design Building containing the first public lift.) architects the chance to produce iron on much more modest scale at Longdon-on- Bogardus' buildings caught on fast as they structures for an entirely novel set of require• Tern in 1795. were available ex-stock in kit form and it took ments and this they did. Lime Street, Then came the Forth Bridge designed by the concerted efforts of the New York Liverpool 1836, Euston, the Trijunct at Derby, Messrs. Fowler and Baker, built between Architects to have fire codes changed Temple Meads and York are all early 1883 and 1889 and representing a scale effectively to put an end to his challenge to examples. This new-found opportunity to change in the possibilities of steelwork their province. derive new and appropriate solutions in new construction. It too attracted influential materials and for new uses did not go About this time the initiative in building critics. William Morris said 'There never unchallenged. How dare classical style be frame design crossed the Atlantic, would be an architecture of iron, every ignored. Pugin in his 'Apology for the Revival germinated, then took a leap forward with improvement in machinery being higher and of Pointed or Christian Architecture' felt that the manufacture of steel sections which, higher until they reach the supremest 28 the Tudor embellishments to Brunei's Temple unlike their iron antecedents, were of higher specimen of all ugliness - the Forth Bridge'. In certain circumstances there are no fire diameters which are an order larger. maintained even though local flange The arch bridge bears a close resemblance Early examples resistance requirements and the steel needs However, the effect is only likely to occur for temperatures up to 800°C were measured. to Lutyens' Runnymede bridge of 1935 of precedent and intuition no protection. When protection is needed large heat-inputs, when columns are heated Results such as these, if generalized, could (though the connection is not thought the following measures may be possible: over two or more storey heights. greatly extend the design method. In the deliberate) and also with Arups' own bridge Design methods are available for replen• original analysis of external fire exposure8 • exploiting the advantages of low stress, Fig. 1 at Runnymede (which deliberately con• ished water-cooled systems which deal conservative assumptions were made about large massivity Temple gateway near Canton strained itself within the earlier precedents mainly with the assessment of the amount of wind effects because of the lack of test data. • placing elements outside the building centuries of precedent though not without modification). water storage needed to replace the water More information about the effects of Substitution of new materials: • cooling elements by automatic water embodied in an 8th century boiled off, and the associated supply through draughts would be valuable. Unaware of the Chinese precedent, intuitive spray building code systems* These methods are related to No requirements for fire resistance designs for bridges appeared in Europe • cooling hollow elements by water filling exposure from the standard fire and take no There are certain circumstances where it is Fig. 2 much later - Leonardo's temporary bridge • placing screens (false ceilings, partitions) account of how the fire might behave in generally agreed that fire resistance is not An-Chi Bridge of 1490 and Rennie's Wye Bridge at between the element and the fire practice. needed on the grounds of life safety: for across Chiao Shui River - Chepstow are good examples. example, single-storey buildings and roof engineer's intuition When it was decided to bridge the Severn at • cladding the element with an insulating Concrete filling material. Such materials can be structures are not usually required by of the same period Coalbrookdale, the natural choice of Because of expansion of the steel, there is intumescent paint, plaster, mineral fibre, regulations to have fire resistance if the material was masonry. But Coalbrookdale negligible cooling effect when hollow cement, concrete. They can be applied escape routes are adequate and there is was the centre of iron making in England in sections are filled with concrete; thus the alone or mixed, and sprayed, trowelled or little risk of fire spread to adjacent buildings. the 18th century and the architect Thomas main structural performance in fire in the form of boards. In other circumstances, however, fire re• Pritchard sought the choice of one 'iron- conditions is provided by the concrete core. sistance requirements are made without any mad' Wilkinson. Not surprisingly the bridge Steel without cladding A very large research programme has been clear indication whether these are for the was built of cast iron, which at least completed but it has not been possible to Fire resistance of protection of the occupants of the building, illustrates how architects can be affected by establish an analytical design procedure. unprotected steel elements or to assist the Fire Brigade to control the passion. The bridge is a good example of Some empirical relationships are available. fire. There is a tendency to assume that Where the performance requirement is how a new material - in this case cast iron Profiled steel sheet floors providing fire resistance for every element of dictated by building regulations then it is - is merely substituted in a solution for Profiled steel sheet may be used either as a structure must automatically increase safety clear that one must aim to provide a fire which a precedent already exists. The link in non-composite shutter or as fully composite for the occupants, when in fact other resistance of at least 30 minutes. For a given this case is the pattern maker whose skill in flooring for reinforced concrete slabs. When measures, such as smoke control or grade of steel and stress level, the fire forming the casting moulds parallels his resistance varies inversely with the 'section used as a composite floor it is difficult to automatic sprinklers, could be more ability to manufacture timber centring. factor' P/A m - 1, where A is the cross-section gain acceptance for more than Vz hour of fire effective. However, it is difficult to analyze area and P the exposed perimeter. Most steel resistance unless cladding is applied to the the problems and find the best solutions elements in common use have a section exposed face of the steel sheet or extra when the purpose of the regulations is not Bridge design 1 made explicit. There is no agreed basis factor of 250m - or greater and for an reinforcement is placed in the concrete. Fig. 3 unprotected mild steel element with the There is as yet no wide agreement on the available which defines acceptable levels of Runnymede Bridge by Lutyens 1935- usual design stress this gives a fire way to design such floors for fire resistance. fire safety for structures, taking into account Precedents resistance of about 15 minutes when the See also the section on profiled steel sheet the seriousness of the consequences of (Photo: Ove Arup & Partners) element is subjected to the standard fire and concrete floors. structural failure for either life or property. • resistance test. ('Massivity' is the inverse of Low fire exposure - internal It is by no means clearly established what the section factor). If the fire exposure inside a building is the performance of each element of sufficiently low then it can be established structure should be during the course of a To achieve larger periods of fire resistance it that the steel elements do not reach critical fire. For example, is it necessary for each is necessary to vary, either singly or in Fig. 4 temperatures and the standard fire exposure element of wind bracing to be protected? Is combination, the section factor, the stress Runnymede Bridge by Arups 1979 is not relevant. The best known example is the loading during the course of the fire level and the grade of steel. A column with changing significantly - either for the better Precedents with a certain style 1 car parks where tests have demonstrated P/A = 29m- (equivalent to a solid 140mm or for the worse? It has been suggested that (Photo: Ove Arup & Partners) that a fire involving a motor car is small and square) would give 30 minutes fire resistance if the wall and roof panels of an industrial 1 is not likely to spread to adjacent cars. In P/A = 11m- (equivalent to a solid 360mm building are destroyed quickly by fire, then addition, statistics indicate that the risk of square!) would give 60 minutes (average the steel frame is very under-stressed and fire occurring in a parked car is so low that it temperature of 540°C)3 can survive without cladding. This would has not yet been quantified. The relationship between fire resistance and certainly explain why unprotected portal Fire exposure may be low because there is a stress level can be estimated fairly readily frames in practice behave better than could small fire load in relation to the for elements with uniform temperature be expected when exposed to accidental 2 compartment size and ventilation. Methods distribution . However, it has been observed fires. A design method for unprotected portal in fire resistance tests that the temperature of calculating the potential fire exposure frames is available9. of steel beams varies both along and across already exist and a method of estimating the Steel with cladding the section and failure may not occur even distribution of severities of fire exposure in rooms (total burn-outs), using results of fire when the temperature of the lower flange In the selection of a material for fire load surveys, has been developed5. These exceeds 600°C. At the moment, since cladding, the designer takes into account analyses could be combined with statistical calculation methods assume a uniform the following factors: temperature distribution, correction factors data on accidental fire behaviour to provide have been introduced2. an estimate of the risk of a burn-out • suitablility for use and method of occurring. The beneficial effects of installation (architectural, environmental, Water cooling automatic sprinkler systems could also be technical and economic aspects) Water filling of hollow sections has become included. The types of low fire load buildings • thickness of the cladding according to the a well-accepted method of keeping steel for which such an approach could be cool without the use of cladding. The main fire resistance required (whether by test or profitable are low-rise schools, offices, by calculation method) problems are the avoidance of dry patches hospitals, sports halls and concourses in of steel which would overheat, and the bus stations, train stations and airports. • maintenance of its integrity and insulating provision of adequate water to replenish that Low fire exposure - external properties. which boiled away. A simply-filled column It is well established that at certain positions without replenishment can provide over 30 Results of standard fire resistance tests outside the facade of a building the fire minutes fire resistance, but not as much as In principle the designer considers two exposure will be so low that cladding of steel 60 minutes. Existing systems therefore aspects: elements is not needed. The external fire usually incorporate storage tanks and also exposure varies not only with position but • the heat transmission through the may provide extra water by inter-connection also with fire load, window area and shape, cladding material and the consequent of columns. Much interest has been shown temperature rise of the steel in the possibility of using simply filled non- compartment area and shape. replenished columns for two-or perhaps Design manuals are available to calculate • the structural behaviour of the heated three-storey buildings, the water in the top the external fire exposure and the steel element and the temperature or 6 7 storey being used to replace that boiled off consequent steel temperature . The design temperature distribution at which a should a fire occur in the lower storey. method has been used to calculate an critical condition occurs However, the likely flow pattern within the average temperature across the section, by and for these the necessary data must be heated column is not well established; it has analogy with interior steel elements. provided by tests. In practice, the only been suggested, for example, that the two- Although it was known that in practice there information likely to be available is the result phase flow of steam bubbles and water could be large temperature gradients there of a standard fire resistance test which gives Fig. 5 Fig. 6 could give rise to surging and large water were no test data available at that time the failure time for a specific steel element Longdon-on-Tern aqueduct Pont-Cysyllte aqueduct by Telford 1795-1803- losses. Existing data for two-phase flow which assessed the importance of this protected by a certain thickness of a specific by Telford 1795- Hailed by Sir Walter Scott as the greatest work have been obtained from tests with small effect. Later research with external material. It is difficult to separate out the an intuitive trial of cast iron of art he had ever seen diameter pipes (of order 25mm) and cannot column/beam assemblies under load information needed if the results of the test for a greater project (Photo: Architectural Association) be extrapolated with confidence to showed that mechanical stability could be are to be applied more generally to assess. Working stress method Ductility Permissible stresses and deflections are Design of composite sections by the working To ensure a ductile response of the beam based on extensive load testing and are stress method is in accordance with elastic there is a requirement that the depth of the nominated in the manuals. theory using a transformed area approach neutral axis of a T beam shall be not less Fireproofing and assuming no slip at the concrete steel than 16% of the overall depth of the section. Based on full scale fire tests, design criteria interface. The area of slab in tension is Shear connection have been determined under which, for given neglected in calculating the area. The function of the shear connector is to slab thicknesses, the provision of fire Rules are given for calculating the effective transmit horizontal shear between the emergency reinforcement will enable fire moment of inertia and effective section concrete slab and the steel beam and to resistance ratings of up to three hours to be modulus where profiled sheeting is used. ensure that there is no physical separation. achieved. This means that only the Permissible stresses are the relevant values Regardless of the method used to determine supporting steel beam requires spraying or in the steel and concrete codes. the flexural strength, shear connectors are other measures to achieve a fire rating. The designed by the load factor method. provision of this reinforcement has been Serviceability Characteristic strengths of both stud and established for given spans and Stress channel connectors are given for various superimposed loads, and is usually a For unpropped construction the stresses in concrete strengths. Connectors are provided considerably more economical way of the steel beam must not exceed 0.9 Fy under to resist the whole of the compressive force achieving the necessary fire rating than serviceability loads. and are usually distributed uniformly spraying the metal deck soffit. Deflection between the points of zero and maximum Practical considerations Deflections can be calculated using a moments. Where beams support heavy Shear studs welded through the decking are modular ratio of n for transient loads and 3 n concentrated loads, distribution should be the usual method of shear connection with for sustained loadings. A general deflection according to the shear force diagram. the concrete slab. It is important to ensure limit of span/250 is suggested with span/ 500 Transfer of longitudinal shear in concrete that there is an adequate power source and or an absolute value of 20mm where damage It is necessary to check potential shear that the interface surface between the could result from deflections. failure planes to ensure that the horizontal decking and the steel beam is clean, dry and Deflections during the construction stages, force can be transmitted to the concrete. The free from loose rust or scale. particularly for unpropped construction, code requires minimum transverse reinforce• Consideration should be given to applying should be borne in mind when considering ment to cross the shear planes in the bottom the studs in the field rather than the fabric• the need for cambers. of the slab. ation shop because of the risk of riggers Vibration Composite decking erecting the steel tripping on the studs. Comparatively light structures can result An Australian code covering composite Stud shear connectors adequately fix metal from composite design and the Australian slabs is yet to be prepared. At present only decking to support beams. Alternatively code gives guidelines aimed at limiting two types of decking are available for use in puddle welds can be used. damage to the structure or discomfort to the composite deck construction. Propping of the decking may be necessary to occupants. Both deckings are galvanized and available limit deflections during concreting. Altern• (a) Floor frequency should be greater than 5 in two thicknesses. Design manuals enable atively, propping can be avoided by locating Hz for occupancies such as residential selection of slab thickness and negative the support beams at appropriately close floors and schools. mesh reinforcement for simple loading spacings. Figs. 3-4 (b) Floor frequency should be greater than 10 situations. Full design procedures require: If there is no propping, deflections can be of Bush Lane House, London. Hz for repetitive activities such as sufficient magnitude for the concrete (a) Check on panel stress during Designers: Arup Associates. dancing, unless there is a large amount actually placed to be significantly more than construction loading (Photos: Arup Associates) of damping. (b) Check on panel deflection under the quantity calculated from the theoretical (c) Transient vibrations can cause discom• construction loadings thickness. fort or annoyance to occupants, and (c) Shear under construction loading Soffit fixings for example, the protection needed for other are nominally the same will vary from fire resistance in excess of 30 minutes either specialist literature should be consulted. For soffit fixings to hang ceilings, ducts, (d) Total panel stress due to slab dead load steel sections, for other periods of standard laboratory to laboratory: This is not the steel sheet must be insulated by a (d) For further guidelines reference can be pipes, etc., the metal decking must be and superimposed loads fire exposure or for non-standard fire surprising since, apart from any differences coating or suspended ceiling or the concrete made to a paper by D. L. Allen: drilled. Flash welding pins are not regarded (e) Shear and bond on the composite slab exposures (compartment fires). in heating characteristics, the real degree of must have reinforcement. Although 'Vibrational behaviour of long span floor as satisfactory. In the case of Bondek The most commonly used method of restraint of the specimen is quite often numerous fire resistance tests have been slabs'. Canadian Structural Engineering (f) Deflection of the composite slab special nuts can be fitted into the flutes to exploiting the results of fire resistance tests unknown and may vary during the test. This carried out, it is difficult to generalize the Conference Proceedings, Toronto 1974. (g) Concrete stress in the composite slab. support lightweight ceilings. is to assume that failure is related to the is particularly a problem with slender information received so that a design attainment of a critical steel temperature columns. method can be provided. Most tests have and to devise scaling methods or charts It can well be argued that the standard fire been for statically determinate floors: better based on a simple model of heat transfer resistance test is only a blunt instrument performance has been measured with from the furnace, through the cladding, to and in practice it serves its purpose because continuous floors. Although in some Precedent in design arises from a number of upset when some of the parameters change the steel. This method avoids any definition there have not been any serious structural countries the failure criterion for a floor is a Precedent sources - legislation, materials, manu• either in the problem or its solution. The of the structural behaviour or thermal failures in fires. If this is true it can also be deflection of span/30, these slabs can reach facturing constraints, form and appearance precedents remain - an early steam engine characteristics of the cladding; it provides argued that calculation methods are just as a deflection of span/20 or more while still and intuition - and our own ability to analyze problems. is given a fluted chimney representative of extrapolation of the result for the particular likely to give the 'correct' answer and are retaining load-bearing capacity. A failure The danger in following a precedent is when Greek Order. Only later and possibly in mode of failure experienced in the test. It much cheaper. It then follows that the fire criterion of infinite rate of deformation is in design the context changes so that the solution is partial recognition of this estranged can be used to predict results for standard resistance test should be re-designed so as therefore more appropriate. Heat transfer situation is an intuitive solution developed fires, but not for compartment fires. One way no longer appropriate. to provide information for these calculation calculations have not so far been very - result outcry. But the general solution for of extending the use of standard test data to John Roberts Extrapolation requires care. Precedent methods. successful probably because the method relieves Society's concern about radicalism chimneys continues to be adopted and it compartment fires is to establish an needs to be more complex for concrete than but can lead to anonymity and irrelevance. becomes a norm. And so the life cycle of the equivalence between the standard fire and Suspended ceilings for steel. design process repeats itself. compartment fires in terms of their heating Fire resistance tests have demonstrated the Overture Derek quoted Blake's 'Auguries of Inno• Composite steel and concrete beams effect on the structural element, the effect value of suspended ceilings for the No seminar is complete without an historical cence', 'we are led to believe in a lie when we To illustrate the impact of precedent and Tests have been carried out with both being attainment of a certain critical protection of steel beams and floor systems. review of the subject in question. It allows us see with, not through the eye'. intuitive thinking on the design process, isostatic and hyperstatic beams for varying temperature. A calculation method has been proposed to compare past achievements with present Intuition on the other hand is our ability to Derek chose a number of key events in conditions. Some large temperature which could be used to generalize test data, efforts. Derek Sugden's talk was as timely as find new solutions to novel problems. It history when either the problem set the gradients were measured in the steel, but the main problem is probably the it was fascinating. He led his audience, requires that we cast aside predilections and designer changed - in context or scope - Deficiencies of the standard test between the flanges and over the supports. difficulty of ensuring that the ceilings are through the mysteries of design achieve• solve the problem on its own merits. Voltaire or when new solutions presented themselves An examination of standard test procedures A calculation of critical temperature installed correctly in practice. The detailing ment from early China to just short of the in the 'Temple de Gout' summed up his - either from developing technology or the and the results obtained exposes several assuming a uniform temperature across the of the suspension system, lighting fittings, present day. The achievements of present appreciation of intuitive design in this way: skill of an individual. deficiencies. First, it has been observed that section is in reasonable agreement with the etc., is of great importance. day 'luminaires' - his term for the ack• 'Simple was it noble architecture. Each Scherzo: Historical examples of the some cladding materials in accidental fires average of the temperatures measured on nowledged leaders of contemporary design ornament arrested, as it were, in its position influence of precedent and intuition may undergo physical changes not Composite steel and concrete the upper and lower flanges. However, the - were left for another day - a pity. seemed to have been placed there of The conflict in China: displayed in the standard test, because of Structural analysis of composite steel and calculation of the heat flow to the section higher fire temperatures in the compartment. could be complex and has not yet been Of course Derek cheated. The talk was not, necessity.' There are early examples of the precedent/ concrete is difficult to carry out for normal For this reason a high temperature test, attempted. as billed, about the skeletal frame. Instead Throughout history intuitive solutions to initiative dilemma. In 8th century China, the conditions. It is not surprising, therefore, if it supplementary to the standard test, is he talked about the design process. Few design problems have, at least initially, design of timber buildings was highly presents problems of analysis under fire Single elements and frameworks sometimes suggested. conditions. Nevertheless, it ought to be realized, fewer cared for the audience was received a hostile reception, mostly, one regulated by the State through detailed Fire resistance tests are normally carried out Secondly, unless the test is part of a possible to carry out fire tests which would caught on the horns of the theme dilemma. suspects, because they represent a break building codes. These reflected the for single elements. The relationship research programme, the initial properties of lead to a definition of the critical conditions To what extent is (or ought) design to be with tradition. By repeated experience, technology commonly used and dictated the between the behaviour of these elements for failure and lay the basis of a design constrained by our own expectations - however, an intuitive solution becomes appearance of the end product. But this the specimen are not measured. The test when supported in the test furnace and method. 'precedent'; and to what extent is it (or accepted and the general public begins to same society had built a large span masonry load is related to the characteristic strength, when installed in a building is not well should it be) a function of our own associate the intuitive solution with that arch bridge (c.610) and a post and lintel not the strength of the sample tested. Profiled steel sheet and concrete floors established. Work on loaded external 26 immediate emotion - 'intuition'? particular problem. This happy balance is bridge (c.820). Thirdly, the results for test specimens which Test data so far obtained indicate that for column and beam assemblies shows greater load-bearing capacity can be obtained than in all countries but Great Britain and Italy, required level of safety should be stated and would be expected by considering the being either a fixed value or one established methods of assessing the potential hazard in the elastic plastic range helped to explain failure will occur that the Australian column in isolation. An understanding of the by calculation. Italy recommends some fixed should be agreed. It would then be possible Composite frame the redistribution of stresses occurring in Standard 2327 Part 1 - 1980, 'Simply factors which affect the performance of values for unloaded structural elements. to determine the level of structural fire the various components in this range. The supported beams', contains a requirement assemblies might lead to the reduction or Unprotected steelwork protection needed, if any, and the effect on and metal deck British Standard Code of Practice, CP 117: related to ductility. This Australian code has elimination of part or all cladding for the All countries except Sweden have buildings this level of employing alternative protective Part 1 published in 1965, was based on been based on CP 117 but it is expanded to lower standards of fire exposure. The with unprotected external steelwork. Only measures such as automatic sprinklers. construction simple plastic theory using idealized stress- include sections on serviceability and it also research carried out so far has not yet one, Italy, has agreed design rules. Clearly this is a wider subject than the use of strain relationships for both steel and covers the use of profiled steel sheeting in reached the stage at which critical All countries accept unprotected steelwork steel in building construction. Ian MacKenzie concrete. For the latter an equivalent yield composite frames. It specifically excludes conditions can be defined. for single-storey buildings (in Belgium for Structural performance stress of 0.85 F'c was adopted. Using these dynamically loaded structures and bridges. Research on columns has so far been industrial buildings only, in France, Germany The development of a calculation method for criteria there has been good agreement with Future issues of the code will cover directed towards axially loaded members. In and Italy only sometimes) and for roof the fire safety of a structure, which could be Introduction the ultimate loads for a range of beams but continuous beams, slabs and columns. practice there will be combined normal structures (only sometimes in Germany and integrated into the methods for structural This paper covers the use of steel decks and stresses and deformations have been less General design provisions of AS 2327 forces and bending moments but the effect exceptionally in Belgium). Seven countries design at normal temperatures, is hampered steel frames acting compositely with satisfactory. The slab which is acting compositely with is not well understood. It has been accept unprotected steelwork for car parks first of all by the present system of grading concrete slabs in buildings. This is a form of Research has continued into the effect of the steel frame may be either: suggested that compression properties at (in Germany, Italy and Sweden only construction which in some circumstances single elements in a standard test and slip at the shear connection and more (a) Cast in situ on removable formwork high temperature may be more favourable sometimes, not accepted in Belgium and second by lack of knowledge of the has proved economical in high rise office accurate moment-rotation curves have been (b) Cast in situ on profiled steel sheeting than tension properties. However, there is a France). Switzerland alone accepts behaviour of structural assemblies and the buildings in Australia. derived. A more realistic assessment of the (composite decking) lack of data to confirm this hypothesis. unprotected steelwork for any building with loads acting on them in real fire conditions. There is now a considerable accumulation of influence of residual stresses in the steel The standard fire resistance is not designed low fire load (less than 60M cal/m2 which is The information needed would include: knowledge about the behaviour of component has also been made. Typical (c) Cast in situ concrete on precast 2 formwork which is left in place to test vertical members in tension. The equivalent to about 14 kg/m of wood). • a study of the present standard test composite members. The codes of practice moment-curvature relationships are shown critical condition must therefore be defined Criteria for fire resistance method, so that it can be adapted, altered permit composite frames to be designed as in Fig. 1. Beams of the type represented by (d) Precast for its full depth. Curve 1 reach a peak and then fall away by calculation, since conventional critical Centres in all but two countries - France or extended to provide more information equivalent steel frame structures by the so- There are design requirements to cover rapidly leading to a sudden failure. Beams temperatures derived from loaded column and Sweden - think that the standard fire for design purposes called 'simple design method'. This was first flexural strength, serviceability, shear tests may not be correct, particularly when resistance test should give more information introduced into BS449 in 1932. A major with the type of deformation represented by • a separation and definition of its strength connection and transfer of shear the hanger is a special steel. At present no updating in 1949 led to lighter beam sections Curve 2 are subject to some strain hardening on the materials at the end of the test and all function, as a heating mechanism and a strength. Rules are given for effective width guidance is available. but it also resulted in heavier columns. and fail in a gradual or ductile manner which but two (France and Germany) would like loading mechanism, would show how and effective thickness of slabs. Properties of steel at high temperatures Professor Baker turned his attention to the is more acceptable to designers. more information on adhesion of the results could be applied when data are Stresses associated with slab flexure are not The tension properties of mild steel at ultimate failure of steel frames and his work It is with a view to ensuring that this type of cladding. Only one country (Austria) has a provided by the following: required to be added to those due to temperatures up to 600°C are well code of practice for the application of • a study of the critical conditions for composite action except where prestressing documented, for example, and there are cladding to the steel. Centres in five failure of loaded elements and frame• forces are applied in the direction of the some measurements available for higher countries are in favour of such a code. works. For calculation of these critical Moment longitudinal beams. temperatures. Creep measurements are Centres in three countries (Austria, Germany conditions more reliable data would be Flexural strength available up to 650°C. It is not clear how and Switzerland) are satisfied with their Curve 2 needed for the following: Design can be either by the load-factor important it is to separate out stress- existing criteria for failure of beams and (ultimate strength) method or working stress induced strain from creep-induced strain but slabs. Four countries (Belgium, Great • measurements of the mechanical pro• (elastic design) method. in view of the high steel temperatures Britain, Italy, Switzerland) favour a limiting perties of steel at temperatures above I measured before failure may occur, more rate of deflection, one (France) an infinite 60O°C. Load factor method information may be needed. Tests have rate, and three (Germany, Netherlands, • assessment of the loads which should be The ultimate moment of resistance is confirmed that mild steel elements, which Sweden) favour a limiting rate for certain deemed to be acting under fire conditions calculated on the basis that: have not exceeded the critical temperature structures only. - wind load, live load, dead load. Curve 1 J (a) The portion of the steel beam in tension for failure, regain their elastic properties Insurance requirements Some of these studies are of a long-term is stressed uniformly to the yield stress after cooling. All Centres but one (Great Britain) said that basic nature, but much information which Fy. Mechanical properties of cold-formed steel insurance requirements discourage the use already exists could be exploited with the (b) The portion of the steel beam in com• C-sections for temperatures up to 650°C are of steel in some or all buildings. addition of a little more data. pression is also stressed uniformly to General comments also available. References yield stress Fy. Use of cold formed sections (1) BEHETS, J.F. and LAW M. Study of (c) The compressive stress is assumed to be The comments and observations reveal a Fig. 1 The use of lightweight cold-formed steel research into the behaviour of structural a uniform stress block of 0.85 F'c sections to replace timber studs inside number of problems: a lack of knowledge of 'Standard' steel elements exposed to fire. Report to 0V (d) The concrete has no tensile strength. fire protection on the part of the building forms of moment: partitions has been studied and a European Coal and Steel Community, authorities; an unjustified prejudice against curvature relationship Curvature 0 Ultimate moment of resistance M'r for calculation method devised. Tests have Centre Belgo-Luxembourgeois d'lnfor- the use of steel on the part of both building neutral axis within depth of concrete shown that these sections can also perform formation de I'Acier, Brussels. Ove Arup authorities and insurance companies; lack satisfactorily as columns and beams when and Partners, November 1980. D-dn M'r = 9 FyAs dg + ' enclosed in cladding materials but the of a clearly stated performance requirement (2) EUROPEAN CONVENTION FOR CON• 2 results have not yet been generalized to give in the building regulations - what are they 0.85 F STRUCTIONAL STEELWORK. 'European c a design method. trying to achieve and how do the fire FyAs 0.85 F'c bD the various Steel Information Centres in Priorities for future activities and research From the investigations described in the (4) BOND, G.V.L. Fire and steel construction. Western Europe. Replies were received from (Refer to Fig. 3) Centres in nine countries. preceding chapters we concluded that the Water-cooled hollow columns. Con- wider and better use of steel in building will strado, 1975. Fire exposure and fire resistance calculation He = FyAs mainly be achieved by a reform of Fig. 2 All countries favoured the acceptance in (5) COWARD, S.K.D. A simulation method for Hcc = 0.85 F'c bD regulations based on: national regulations of a calculated design estimating the distribution of fire Hsc = FyAc where Ac: Area of steel fire, taking into account fire load, ventilation • a more precise definition of performance severities in office rooms. Building compression and compartment size, as an alternative to requirement Research Establishment Current Paper 0.85 F 0 85 F the standard fire resistance test. It is • a more precise estimation of structural CP 31/75, April 1975. r For equilibrium: accepted generally only in Sweden. performance and for designers: (6) AMERICAN IRON AND STEEL He =Hcc + 2Hsc f t ' ' FyAs = 0.85 F'c bD + 2FyAc In only three of the countries (France, • design manuals for the structural INSTITUTE. Fire-safe structural steel. A Sweden and Switzerland) is calculation of design guide. Washington, D.C., 1979. engineer Hcc As-a85FCbD the fire protection needed generally Hence Ac = 0.5 • simple design guides for the architect (7) LAW, M. and O'BRIEN, T. 'Fire safety of "i-fcf 2 H Fy accepted as an alternative to standard fire and engineer which show how much bare external structural steel'. Constrado, resistance tests. The other countries were in protection, if any, is needed for the 1981 dn can then be found from properties of steel favour of calculation, but one (Germany) only structural steelwork. (8) LAW, M. Fire safety of external building CG of steel beam sections. The code then gives a formula for sometimes. Performance requirement elements - the design approach. Eng• H? determining the ultimate moment of CG. of tension Only two countries (Sweden and A performance requirement should state the ineering Journal. American Institute of resistance when the axis N-N is located in Switzerland) have agreed representative objectives of providing fire safety - whether Steel Construction, Second Quarter, pp the flange or in the web of the beam. values of fire loads for a range of buildings; it is for the protection of people (occupants, 59-74, 1978. AS 2327 contains clauses which modify the the Netherlands for office and residential neighbours, fire fighters), the protection of (9) CONSTRADO. The behaviour of steel 2F, assumed stress block when the depth of buildings only. property (contents, structure, neighbouring portal frames in boundary conditions. Fig. 3 stress block would theoretically be located 8 A 'critical' steel temperature can be defined buildings) or a mixture of both. Ideally, the Constrado, 1980. below the top of the rib of the decking. vertically between roof and floor. Horizontal ribbed metal cladding to stabilize the open the base width and method of installation. Also, the angle 8, between the bracing and sides of the trough enabled us to provide a Towers and They are fabricated and transported in the leg member, should be maintained within 150mm overall thick frameless walling relatively large sections to minimize erection the following ranges: system. This system was designed, tested flare stacks time. Aggressive environmental conditions o and successfully used in a pilot scheme and infrequent 'safe' access periods are bolted structures 20°<6<90 where no commercially available system taken into account by specifying high quality welded structures 30°<9<90o could be found. John Tyrrell materials and workmanship. Solidity ratios: Central Bank of Ireland head offices Transmission towers are required to support Typically solidity ratios for different widths This design was conceived as a major land• Introduction the overhead power supply lines at relatively are as follows: mark in Dublin city centre and is unique in its Towers are by implication tall structures that frequent centres. The power lines are reach above the surrounding environment. tensioned to reduce the catenary effects and structural design in Ireland. Measuring 45 x Panel width Solidity ratio 30m, its seven floors are suspended from the They are commonly used to support suspended from an arm arrangement as part < 1.5m 0.25 roof and supported by two concrete service equipment or some installation at a required of the tower. This in turn creates forces in the < 5.0m 0.20 towers. elevation as part of an engineered system or tower in addition to the wind load. Also tensions in the power lines are affected by <10.0m 0.15 All floors are formed of structural steel process. climatic temperature variations. Because of <10.0m 0.10 trusses with a thin concrete slab. Each one The greater part of our work in this field has the number of towers required for any one is suspended by 12 pairs of Macalloy bars on been associated with towers supporting Factors affecting the design system the cost penalty for conservative the perimeter, directly to roof level. A system microwave antennas but more recently we design could be significant. The design Project requirements normally provided by of roof trusses enclosing the plantroom is have designed a number of structures for approach therefore is to test a tower or the client or the systems engineer include: the primary steel structure carrying all the supporting gas flaring systems and vent number of towers to failure, so the strength site location and particular details that are floor loads into the concrete cores. Floors pipes. Similar structures that we have of all members, including those normally known to provide a constraint of one sort or were fully assembled at ground level and designed or analyzed include lighting assumed to be redundant for analysis another on the design jacked into position, using the British Lift towers, towers supporting water storage purposes can be properly evaluated. Slab heavy lifting system located on the tanks as well as guyed structures. However, basic wind speed, the combination of wind and ice accretion and temperature where roof. this paper concentrates on microwave General tower arrangement appropriate Papal cross and canopies: towers and flare towers. In cases where the tower geometry is not size, type and number of items to be Phoenix Park, Dublin Fig. 6 Central Bank of Ireland head office under construction. Architects: Stephe Clearly there are similarities between the given or determined by factors other than supported at specified levels including An inception to completion period of two Gibney & Associates different types of structure but the strength or deflection the following operational or performance requirements of associated feeder systems months was achieved for the erection of a empirical rules for microwave towers may be the system determine the functional limits on the twist and tilt for the structure 35m high steel memorial cross for the 1979 applied as a first stage towards achieving an requirements of the structure in each case. design life of the structure Papal visit to Dublin. A fabrication using six economical design. Steel is favoured largely because it can aircraft warning lighting universal beam sections, each 600m deep, to Slenderness: easily be fabricated as component parts and painting and protection. form both stem and arms was devised, The ratio of the overall tower base width then transported and erected relatively On occasions we may be required to carry designed, fabricated, painted and erected should not exceed the values tabulated quickly and simply in remote locations. out wind speed investigations where with very little time to spare. below. Types of structures sufficient details are not given. Also, it is quite frequent that further interpretation of There are two main generic structural forms: Tower Maximum Fig. 7 self-supporting towers and guyed arrange• height deflection the design requirements is necessary. Papal Cross being hoisted into ments. Self-supporting towers are normally 0.75° 1.2° 1.2° In addition to the specified requirements position - Phoenix Park, Dublin of the open lattice type and may be either there are other factors that are likely to 50m 6 8 10 square or triangular in plan. Guyed influence the design such as economic and structures may comprise a vertical or 50-100m 5 7 9 practical considerations. For example the inclined slender stem with the stiffness 100-150m 4 6 8 availability of steel sections locally, provided by the guys. The combinations and transportation, lifting and erection, the Fig. 8 applications of these types of structure are Top width: maintenance of the structure and the Papal Cross and canopies as seen too numerous to cover adequately in this 2.25m for square towers with internal equipment including access are all parts of during the Papal visit to Dublin paper and therefore it is intended to consider climbing ladder; 1.65m for triangular towers the equation. Also, the lightest possible microwave and flare towers only. A brief with internal climbing ladder; 0.45m for structure is not always the most economic, « description of the main characteristics of towers with external climbing ladder. particularly where some standardization can each system is given below. Reference is Leg slope: be achieved and where there are difficult also made to transmission towers where a The slope of the tower legs at the base ground conditions and the cost of the different design approach is adopted and should be such that the point of intersection foundations may be a significant part of the different loading conditions apply. of the projected lines of the legs occurs overall cost. Microwave towers are usually constructed above the two thirds point. Loading from tubular and/or angle members bolted Wind together. For a particular network they are Panel types: commonly arranged as a family or families The optimum height to width ratios of the A basic wind speed corresponding to the 3 of towers. Each family typically consists of a typical panel bracing arrangements are: second gust with a return period of 50 years number of panels arranged vertically. Panels is usually adopted for the design, or service• can then be omitted either from the top or Height/width Panel type ability condition of the structure. On from the bottom for the required height. h/w>1.5 Z occasions an extreme or survival wind speed Each panel is braced in elevation and 1.0riser varies with the particular gas flows up to 1.5m in diameter. Ancillary pipework such as feed lines to the flare tip are also required to be supported. Removal of the flare tip for maintenance is an important feature of the design. These structures tend to be 'one off Fig. 1 and constructed from welded tubular Remote members although not exclusively so. microwave Offshore tower structures frequently have tower site 24 restrictions imposed on the design such as Wind forces on antennas can be obtained Method of analysis dynamic effects should be considered and capable of accommodating two Boeing 747s Usually steelwork is let as a nominated sub• alternative source of supply. There is either from manufacturers' literature based Lattice tower structures are considered as they include: had just been completed. SAA, in contract. We find that this has the advantage however a price differential which has on wind tunnel tests or derived from the three dimensional space frames. Fully tri• fully welded structures where fatigue may be conjunction with a multi-disciplinary tech• of selected tendering as well as a later need inhibited more general use of continental method given in 'Calculation of wind forces angulated structures with bolted significant nical team from the South African Transport for tender information. However, there can sections. and pressures on antennas', by Cohen, connections are assumed to be pinned Services, embarked on feasibility and be difficulties in precise definition of work structures supporting TV antennas, rad• There is limited capacity for economic Vellozi and Suh. frameworks. There are small errors involved conceptual design studies. content when variations arise. On the other iators, particularly at the top fabrication of plate girders and castellated Snow and ice in this assumption such as the legs being It was decided that a hangar complex hand measurement in the Bill of Quantities, tubular members with a slenderness ratio beams. These would normally be imported continuous at the nodes but these effects comprising two major hangars with a central in spite of the apparent precision of the ready-made. Stock holders keep some Snow and ice will contribute to the gravity exceeding 180 where local cross wind are rarely structurally significant. Separate annexe located between them would best information, has not always worked well and supplies and since may jobs are modestly load on the structure but the accretion of ice effects may be significant. on individual members or antennas will checks may be carried out for bending facilitate aircraft movement and at the same selection of tenderers is less controllable. sized the necessity to buy there tends to moments arising from locally applied forces There are a number of computer programs increase the surface area and hence time minimize fire risk. It was decided that There has been a chronic problem in over increase job costs. or eccentricities at connections. For fully available for carrying out a dynamic increase the drag forces due to wind. Icing is each hangar should, if feasible, be a clear capacity in the steelwork fabrication in• Certainly where anything other than Grade welded structures or statically indeterminate analysis. In-house programs include expressed in terms of radial thickness and spanning structure of 150 x 100m so as to dustry in Ireland. There are several major 43 steel is envisaged the lead in period must structures, framing moments must be DYMAST, GLADYS, DAFT and PAFEC but some guidance is given by the Department maximize space utilization. firms who have the resources and expertise allow for mills ordering to be feasible. evaluated. only DYMAST is suitable for a random of Energy in 'Guidance of the design and Our favoured solution comprised a main to tackle any job which has yet been built in The standard facilities available to the larger stochastic analysis. construction of offshore installations'. portal spanning 150m over the doors, with the country. There is also a wide selection of firms provide all the necessary equipment There are two in-house computer programs Detailed design considerations For the icing condition a reduced wind speed available for carrying out a static analysis of three main trusses spanning 100m from the small and medium sized fabricators so that for fabrication for most situations. Design standards is considered and this is in the order of 90% these structures, TOWER and PAFEC. back wall to the portal. We proposed long- for smaller jobs there is an embarrassment Automated cutting and drilling has recently of the design wind speed depending on the Design standards may be specified in the span crane bridges in the 37.5m bays of choice. become available but is still unusual. TOWER was developed specifically for pin- locality. head contract specification according to the between trusses to handle the servicing Welding techniques nowadays almost jointed statically determinate microwave requirements. Technical standards can be variable but Temperature country of origin with reference to more universally employ semi-automatic C02 towers and includes analysis, design and excellent results are possible provided the specific internationally recognized design The main hangar structure systems, at least in the shop. Automatic Loading from climatic temperature vari• plotting facilities. The main members and job documentation and site control are good, Each hangar section consists of steel- welding is rarely done, partly on account of ations is not normally significant for these the secondary members may be specified by codes. In recent years a number of design and the tenders are based on selection. framed structure supported on three sides the scale of work involved. types of tower structures. size in which case a straightforward analysis guides and codes of practice appropriate to Likewise, management can be uneven and by braced walls and on the fourth side by a Most fabricators do not employ welding is carried out. Otherwise the program tower structures have been published. The tends to be skimped when resources are Temperature effects due to hot or cold gases pinned base portal frame of 151.2m span. performs an iterative analysis of each panel, main ones are: stretched, either technically or financially. technologists and this service combined in the risers and due to radiation from flaring The roof is divided into four equal sections of selecting from library files those member (1) BS6235:1982 with NDT interpretation is provided by one or may induce local stresses and possibly 38.8 x 100m, each of which has a suspended The potential is certainly there to achieve sizes not specified, until a satisfactory Code of practice for two freelance specialists. By and large this influence the choice of materials. system of runway beams for the support of very high standards if sufficient input is design is achieved. fixed offshore structures. arrangement is satisfactory but difficulties Waves cranes and general purpose maintenance provided and the work well supervised. (2) Department of Energy 1982 can arise where the fabricator does not Offshore structures such as towers mounted Deflections and rotations are calculated at platforms. Three main trusses span 100m realize when he is out of his depth. We tend Offshore installations: Design is normally to BS 449 and the BCSA on platforms may be required to withstand the top of the tower, at the top of each panel from the west wall to the main portal at to use radiography and ultrasonics, partly as guidance on design and construction. Handbooks are universally available. The wave loading. The effects are usually and at the level of each applied load. The 37.8m centres. normal source of materials is the UK. There psychological tools to convey the im• foundation forces are calculated at each leg {3)APIRP2A: 1982 assessed by applying an appropriate The roof structure supports the moving is a degree of continental influence and portance of workmanship as much as the of the tower and steel weights are totalled by acceleration input to the base of the tower. (American Petroleum Institute) loads from the cranes and service platforms during times of BSC strikes this forms the actual test. Generally this works quite well. member type and steel grade. Earthquakes Recommended practice for planning, as well as the necessary lighting, fire designing and construction fixed offshore Earthquake loading is rarely significant in In most cases self-supporting lattice towers protection services and the comfort heating Building types Descriptions of some individual buildings the design of towers. In seismically active are not dynamically sensitive. As a general platforms. system. Advance factories Bailey's Irish Cream factory areas the effects are considered by applying guide, structures having a fundamental (4) DnV (Det norske Veritas) The 150m span portal, with a mass of 262 Most advance factories are sponsored by the This is an 18,000m2 building which utilizes, a base acceleration obtained either from an period of oscillation less than three seconds Rules for the design, construction and tonnes, was assembled in sections on the Industrial Development Authority who share for the first time in Ireland, the 'Nodus' appropriate ground response spectrum or can be designed safely on a quasi-static inspection of offshore structures. ground, welded and then jacked up 25m into the work among many design teams. At this system on a large scale. CHS concrete-filled from a response time history. basis. There are exceptions to this where (5) Draft Code of Practice 1978: position at the top of the legs. The main level concrete competes strongly with steel columns at 19.6m each way support the Lattice towers - loading. trusses were lifted in sections on to trestle and is probably a bit cheaper currently. space frames which number 43 in all. Each supports and welded in situ. The entire Fig. 2 These documents tend to complement each Systems of two-way trusses (bolted in one was assembled at ground level and lifted structure remained supported on the trestles Jebel AM microwave tower, other in particular areas but they also refer direction) have been used but more recently into position. A 'Mero' truss portal spanning until it was completed and then a system of designed by Ove Arup & Partners to national design standards and some one-way members in alternating directions 19m is used to support the entrance canopy. jacking it down to release the supports was (Photo: Mike Shears) interpretation is often required. in adjacent bays have been found to be quite Geffy Corporation factory implemented. successful, almost equally effective, and This is a modest 2,000m2 factory notable for Strength and stability The structure is stabilized through bracing in cheaper. its unusual use of concrete block vertical Where no other design standards are given, all three walls which interact with the portal Purpose designed factories structure. However the steel is also the strength and stability of towers are most stiffness to provide stability. In-plane bracing A large diversity of structural form has been interesting, using 686 x 152mm castellated commonly assessed on the basis of the is provided in the roof. utilized to fit specific briefs. They range from universal beams (CUB) as main beams on a design approach given in BS 449. The Roof drainage is provided along valleys, portal frames to Nodus, depending on the 15m, 3 span grid and lighter CUB of the same permissible stresses incorporate factors of dimensions as secondary beams in alter• midway between the main trusses, the brief, the client's cost consciousness and Fig. 3 safety against failure in the range of 1.5 to nating orientation. Continuity of main beam ridges being over the main trusses and at the the architect's powers of persuasion. Microwave tower 1.7. As wind is a predominant loading feature over the circular hollow section columns, ends. Office buildings under construction in Nigeria, on these structures we tend not to use the using 8.8mm bolts, permitted the use of A feature of the structure is the neatness of Since office buildings really got going about designed by Ove Arup & Partners 25% overstress permitted by BS449. dimensionally identical main and secondary detailing of the main members and their (Photo: Mike Shears) Foundations are designed to have a factor of the mid '60s it has been quite unusual to find beams which nicely unifies the design and connections. The maximum force in the 17' safety in excess of the tower structure. The steel frames. Their use is usually confined to facilities service runs. / factor of safety appropriate to uplift, down- chord of the main portal is of the order of penthouse level. thrust, sliding and overturning is a minimum 25,000 kN. The major members are H or Sports halls Factory walling value of 2.0. It is also advisable to check that channel sections built up from up to 38mm These invariably use steel roofs and often We have been involved in the development of an adequate factor of safety exists for an plate. The result is a clean appearance on steel columns, as the scale tends to be more a steel factory walling system to meet a extreme or survival wind condition. both external faces of the steel members, modest than elsewhere and comparatively particular brief. This uses 1.2mm thick with a minimum interruption by gussets. little scope for the spectacular has been galvanized metal in interlocking trough form, Deflection Hangar doors available. 500mm wide x 100mm deep, spanning 7m This may be considered as a serviceability Each hangar has four door sections moun• limit state for the design of microwave ted on a twin track system to close them. towers. The acceptable limits of deflection The track system is continuous from one end vary from aerial to aerial which in turn are of the complex to the other so that in the related to the frequency band of the event of one complete hangar frontage microwave system. Tall, slender structures needing to be opened, all four door sections ! will tend to deflect more than fatter ones for are moved to the frontage of the other » the same applied loading. However, the mm hangar section. Each door section member sizes for slender towers may be comprises two leaves with a fixed link larger than the equivalent members for wider between them. Each leaf has its own drive v towers to carry the applied loading. On the mechanism. other hand wide towers tend to require more / bracing and will therefore attract more wind (5) IRELAND loading. The objective therefore is to juggle Ove Arup & Partners in Ireland, founded in Fig. 5 the geometry so that the strength and 1946 in Dublin now operates also in Cork, Bailey's Irish deflection requirements are achieved for the Waterford and Limerick. Total staff numbers Cream factory: T minimum weight of steel. are about 140. Most of the work is located in lifting the Ireland with a small amount in the UK, space frames. Selection of member types Middle East and the Third World. While the Architects: There are three main types of steel sections bulk of the projects are buildings in some Scott Tallon used in tower design; tubes, equal angles form, an increase in civil works content has Walker Ai and cruciform angles. The advantages and recently developed in the practice. Some examples of each type are given below: (a) Civil engineering Most of our work in this field has been in reinforced and prestressed concrete but we have been involved in several interesting projects with structural steel elements. In conjunction with a consortium, Cale• donian Platforms Structures, we developed a design for an offshore oil production platform, Forth 150. This included a steel deck structure comprising 4,000 tonnes of grade 50D tubular steel. The firm are joint engineers with Messrs. Crouch and Hogg for the Kessock Bridge, an important cable-stayed road bridge with a main span of 240m over the Beauly Firth. We assisted by checking and approving the design of the box steel pylons and deck crossbeams in accordance with the Merrison Rules. Further north, on the stormy shoreline of Scapa Flow in the Orkney Islands, we have currently under construction three roll-on roll-off South Island Ferry Terminals in• corporating hydraulically operated hinged Fig. 3-4 steel ramps. Hangar 8, Jan Smuts Airport, South Africa. Architects: South African Railways Fig. 4 Fig. 5 (b) Low rise buildings Brent C flare tower: transportation of prefabricated sections. Arups carried Brent C flare tower: Within this, the largest category, are indus• out dynamic fatigue and analysis checks as well as being responsible for erection of tower sections trial, school and recreation buildings, mainly obtaining certification. We were also responsible for the appraisal of (Photo: courtesy of single storey, where steel comes into its lifting and temporary works. (Photo: courtesy of Sea and Land Pipelines) Sea and Land Pipelines) own, with its lightweight and speedy erection unhampered by the need for fire Figs. 6-7 protection. Fort McMurray flare stack, Canada: erection of guyed riser with riser fabricated in sections and erected in two parts. In spite of strong competition from the Designed by Ove Arup & Partners. (Photo: courtesy of Bechtel International) package dealers there remains a demand for the one-off building for which an off-the-shelf solution does not readily cater. Typical of many school and college buildings 8 we have designed is the games hall at Anderson High School, Lerwick. It is interesting to note that at this site in the Shetland Islands, the most northerly part of the UK, the design wind pressures are very high (twice those for the south of England) resulting in significantly heavier steelwork than would be required in southern parts of tive industries and power generation. The for example, a shopping mall. Bracing to the mainland. use of structural steel in building side walls or infrequent internal masonry construction is very widespread but usually walls is required for stability. (c) Roof structures on a small scale. (d) High rise office buildings While the basic structure of many of our The economic use of structural steel in the buildings is of reinforced concrete or Typically the design of structural steel within the Australian offices of Ove Arup & Partners floor systems of high rise office buildings is loadbearing masonry, steelwork still plays an falls into the following categories: heavily influenced by the speed of con• important role in roof structures where struction. It can sometimes be demonstrated lightweight is often an advantage and added (a) Industrial buildings that the use of structural steel framing and fire protection is not required. Industrial buildings for warehouse and composite metal decking can lead to a In the case of theatres, steelwork provides factory facilities are typically portal frame significantly faster typical floor construction buildings fabricated from universal beam an ideal solution where services and access cycle in high rise office buildings. The l sections. Clear eaves heights of 5 - 6m and can be provided within the structural depth consequent saving in holding charges can spans of up to 30m are common. Wind of the roof trusses. more than offset the higher construction loading is resisted by portal frame action Two theatres which we have recently cost of a steel structure. and braced panels. completed are the Dundee Repertory Theatre (e) Mining applications Prefinished metal deck roofing has largely and the Pitlochry Festival Theatre. Structural steel is commonly used for disadvantages of each of these sections Cruciform angles the tower or parts of the tower to be carried replaced the cheaper asbestos roof The Dundee Theatre is a triumph of ingenuity framing structures in the mining industry. It may not be immediately apparent and they out in the fabricator's yard prior to shipment. sheeting. This is supported on cold rolled They have the same advantages and dis• in fitting a 450-seat auditorium with all the finds applications to heavy duty structures, are summarized as follows: This avoids the situation where errors found Zed purlins. Walls may be metal cladding on advantages as equal angles. associated facilities into an extremely tight platforms, conveyor supports and de- during erection are difficult and expensive to C sections or of masonry construction. Tubular members They require complicated battening and city site. Steelwork is used in the auditorium watering bunkers. A number of commissions rectify. Also, base setting templates are used splicing details. roof, and the flytower structure which rises (b) Roofs to low rise offices and commercial have been carried out for an iron ore Lend themselves more readily to a variety of to ensure that the holding down bolts cast to 18m. buildings processing plant. plan shapes. Fabrication into the concrete foundations match the At Pitlochry, a holiday town in the Highlands Numerically these are probably the most (f) One off structures The range of sizes is greater but they may Knowledge of the fabrication process is steelwork interface. of Scotland, a slightly larger theatre common use of structural steel in each of The Melbourne office have designed 4 steel not be readily available. essential to the detailing of steelwork. It is (540-seat) has been built in rural sur• the Australian offices. An average job would floodlight towers for an athletics stadium. They require special skill in fabrication, also important when considering suitable Conclusions roundings, again using steelwork for the roof contain less than 15 tonnes of steel. They ranged up to 58m in height with the particularly for profiled connections. sub-contractors for carrying out the work as The experience we have built up over a Fire regulations generally permit buildings of the range of skills and facilities available structures. access ladders and platforms contained They are more expensive than angles, weight period of years enables us to respond up to three storeys to be of metal roof from steelwork fabricators both in the UK within the tapered tubular section. They were for weight. quickly to the demands of our clients and (3) AUSTRALIA construction. Flat roofing is adopted on cold designed for dynamic effects and fatigue and overseas is wide and varied. advise them on all aspects of the design and They are structurally more efficient and The use of structural steel within Australia is formed purlin sections supported on conditions. Fabrication drawings are normally prepared construction of tower structures. Our attract less wind load than angles. actively promoted by the Australian Institute universal beams. Mineral wool provides by the fabricator based on engineering analytical tools are sharp and we keep of Steel Construction. This organization thermal insulation. (4) SOUTH AFRICA Equal angles design drawings. It is recommended that the abreast of design development in the related fabrication drawings are checked to fields. arranges seminars, courses and lectures, (c) Shopping centres Hangar 8 - Jan Smuts Airport Best utilized for square towers. publishes journals, magazines and safe load minimize misinterpretation of the design Roofs to shopping centres are similar to The origins of this project date back to 1973 Maximum size normally available is 200mm x A large part of our work is overseas and from tables and it sponsors research as well as those described above but much larger in when South Africa Airways decided that a requirements and inspections of the time to time we have relied heavily on our 200mm. maintaining library information. area. Trusses may be substituted for new maintenance hangar able to cater for steelwork fabrication are carried out to overseas offices for local support. We have The greatest tonnage of structural steel is universal beams for the larger spans. Usually the new generation of wide-bodied jets Easy to fabricate and readily available. check for quality, workmanship and per• enjoyed their understanding and close co• used in heavy industrial works such as the they are concealed above lightweight would be required by the early '80s. At that Cheaper than tubes weight for weight. formance. operation and we hope that this working 22 petrochemical industry, energy and extrac- ceilings, unless they appear as a feature in, time, construction of a 150 x 100m hangar They attract more wind load than tubes. It is common practice for trial erections of relationship will continue. 11 the associated back-up services would have great for a TLP type solution. In addition, the concrete, and, although faster to erect than Almondell Footbridge is a cable-stayed The use of to be placed on the platform. overconsolidated soils of the North Sea Local reports reinforced concrete, the steel-framed struc• girder bridge of 30m span. The simple 19m plated steelwork With a tension leg platform, such as the make the tension foundations economically tures are generally 25 to 35% more expen• high 'A' frame and vierendeel deck produce a example TLP, the operational constraints are viable for intermediate water depths. The summary sive than reinforced concrete. dramatic but pleasing structure which suits in a tension leg the same as those for a conventional fixed details of the application of the TLP to the (2) SCOTLAND the heavily wooded surroundings. platform, since it must receive the same North Sea development can be found The four Arup offices of the Scottish At Kings Buildings the problem of con• elsewhere1. Jim Hannon platform design operational approval. The TLP concept uses practice: Aberdeen, Dundee, Edinburgh and structing a new boilerhouse and chimney a floating vessel, a semi-submersible type Design approach for TLP Glasgow have designed a wide variety of round the existing plant while maintaining a structure, which is connected to the sea-bed Tension leg platform design can make good The following digest is from the papers by: steel structures over the years. continuous supply of heat was neatly solved using steelwork. The cluster of eight new Nick Prescott in such a manner that the vertical tension use of the limit state approach. In the case of (1) David Bedford - Hong Kong Typical of the range are three of our projects 2 legs are kept taut by the vessel's excess the example TLP this was based on the DnV which have received Structural Steel Design steel flues is structurally independent of the (2) Derek Blackwood - Scotland existing brick chimney round which they buoyancy. The vessel configuration chosen (Det Norske Veritas) rules. Static loadings on Awards; The Royal Commonwealth Pool, were built. Introduction to the TLP for the example TLP is a simple unbraced a TLP vessel consist of permanent loadings (3) Ian Mackenzie-Australia Edinburgh, Almondell Footbridge and Kings framework in which the members are formed A fixed offshore oil or gas production (structure and equipment), functional (4) Cliff McMillan-South Africa Buildings Boilerhouse. In recent years our experience in the use of platform structure is designed to provide a from stiffened steel plate components using loadings (consumables and live loads), (5) Finbar McSweeney - Ireland The superstructure of the Royal Common• steelwork seems to have fallen roughly into safe working platform in an exposed marine stressed skin design as in a box girder buoyancy and tension leg loadings. To wealth Swimming Pool is of 280 tonnes of three broad categories: environment. On this working platform the bridge. This concept results in close ensure that equilibrium is maintained, all the for the Arup Partnerships Structural Steel• structural steelwork construction with a roof various processes associated with oil or gas structural interaction between the square work Seminar in 1982. (a) Civil engineering partial load factors (7 f) on these loads have of 78m x 68m in two way spanning steelwork. production must be carried out in all vessel base (the pontoons), the deck (which to be considered as unity and member forces (1) HONGKONG In addition to the perimeter columns, the weathers and without interruption. These contains all the plant and facilities) and the (b) Low rise buildings factored by an appropriate stress factor. This Arup involvement with steelwork in Hong planning of the interior permitted support would include the primary separation of six interacting columns (Fig. 1). stress factor (7p) should be chosen to Kong tends to be limited to specific from a single off-centre internal column. (c) Roof structures. fluids extracted, the control of their export The tension leg designs were originally put ensure compliance with the 'Ultimate limit elements of construction and the design of and the services associated with continuous forward as deep water structures for sea state' as defined in DnV Section 4. temporary works. production. They may also include the equip• depths between 1,000 and 2,000ft. However, Environmental wave and wind loadings can The local fabrication facilities are minimal, ment for the drilling and testing of the wells, the field, at 482ft. in the East Shetland Basin be treated in a similar manner with a partial apart from a few local shipyards which have and for the injection of water or gas into the area of the North Sea, is being developed stress factor (7 p) chosen to be compatible begun to diversify the field of structural field. using such a platform since the TLP has with the DnV recommendations. Table 2 steelwork construction. This means that, With major isolated installations, consider• been recognized as being cost-effective for summarizes the partial stress factors used generally, structural steelwork is fabricated ations of continuous operation would intermediate water depths. Had the process in the design of the operating, extreme, and overseas, thus requiring a long lead-in time, require the platform to be manned round the requirements been radically more complex, fatigue limit states for the Hutton TLP. and once the shipping of the fabricated clock, and hence accommodation units with the platform oayload could have become too Having carrried out analyses appropriate to sections has commenced there is little flexibility to incorporate alterations or Fig. 1 modifications. The requirement of the Building Regulations Schematic view of Hutton TLP and, below-the geometry regarding concrete encasement for cor• rosion protection, etc., and a reluctance to Table 1: Geometry (All dimensions to moulded lines) accept lightweight fire protection, until Length: Between column centres 78.00m recently, have led to all the steel-framed Overall 95.70m buildings erected to date in Hong Kong having their structure totally encased in (O } •4..'.;-.' ' V SY • «> ^ Breadth: Between column centres 74.00m Overall 91.70m Fig. 1 Almondell Footbridge Height: Keel to main deck 57.70m Main deck to weather deck 11.25m Fig. 2 The Royal Commonwealth Pool. Architects: Robert Matthew, Johnson- Draught: Operating 32.00m at LAT Marshall & Partners

Freeboard: To underside of main deck 24.50m at LAT

Water plane: Area 1324.00m2

Columns: 4 Corners 17.70m dia. 2 Centre 14.50m dia.

Pontoons: Height 10.80m Width 8.00m Corner radius 1.50m

Displacement: Approx. 61500 tonnes

Total weight: Including riser tension 48500 tonnes (Approx)

Fig. 2 Fig. 3 Hutton TLP 1.33 model under Hutton TLP tower hull under construction maximum height, maximum steepness, regular in the dry dock at Nigg. waves in NMI main test tank, London Pontoon is about to be lifted in. Table 1: Structural costs of steel-framed buildings theless, these are time-consuming wet each set of loadings, elements can be Table 2. Typical partial stress factors(Tp). trades, and fire protection remains one of checked for the complete design condition Costs at 1980 rates: Rands/m2 the important time and cost drawbacks to for compliance with DnV rules by summing Load categories Operating Extreme Fatigue the effective use of structural steelwork for member forces in accordance with the (1/12th year) (100 year) Penmor Dennehof Garden buildings, due to the limited experience in relationship for element force: the local industry and relatively small Permanent (P) 1.3 1.0 N/A Tower Park Plaza F=2Fl7pi market. Functional (F) 1.3 1.0 N/A Cost comparisons where F, is the element force for load case i, Steel beams R 44.90 R 22.06 R 43.30 and pi is the appropriate partial stress Static Buoyancy (B ) 1.3 1.0 N/A Table 1 sets out the elemental estimating s factor. Using this approach the overall safety Shear studs 2.13 3.70 3.40 components for three typical steel office Dynamic Buoyancy (B ) 1.3 1.3 1.0 factor for the design can be expressed in the D Steel columns and bracing 19.00 structures. Changes in detail could occur - (wave generated) 13.30 15.60 form: _ , ,, for example cement mortar screeds may be Safety factor = 7 .7, y .£ m p Inertia 1.3 1.3 1.0 Steel decking 12.00 11.72 16.00 preferred in certain cases to a power floated

Concrete topping including mesh finish. However, power floating has the where Tm is the partial factor on material Tethers - due to permanent (Tp) 1.3 1.0 N/A advantage of speed and minimum weight. strength, K is the slenderness ratio and i// is and power float finishing 11.00 10.29 9.96 Tethers - due to functional/live (T ) 1.3 1.0 N/A Furthermore foundation requirements would the load redistribution factor. L Temporary propping of deck 2.50 1.72 — have to be analyzed to suit the particular In addition, the use of fracture mechanics in Tethers - due to environmental (TE) 1.3 1.3 1.0 design and site conditions and must be built the design of thick plate members enables Fire protection Environmental (E) 1.3 1.3 1.0 (Plastered or Sprayed Vermiculite) 14.00 13.16 14.42 into the cost estimate. the designer to ensure that the elements Deformation (D) Temperature, lack of fit, etc. 1.0 1.0 N/A It must also be noted that the fireproofing of prone to fatigue damage are not limited by fracture toughness resistance. This ensures R 105.53 R 75.95 R 102.68 structures by spraying demands that the Accidental (A) 1.0 N/A N/A compliance with the basic limit state perimeter of the building be clad with philosophy of preventing potential cata• temporary tarpaulins to avoid material being of the hull is closer to shipbuilding, in bay area, with its riser tensioners and drill strophic modes from dominating the design. Composite action sprayed over the neighbourhood. The rate particular to submarine hull construction derrick support rails. In the case of the present project it also The economic advantage of composite per m2 for the spray application should practice. The TLP deck spans between two The deck is an all-welded structure formed enabled fatigue assessments made with ref• action for both primary and secondary include for this requirement. As a rough lines of three columns, each using three by these main plate girders, or bulkhead erence to SS 5400 Part 10 SN curves to be beams is well-known. Normally the beams guide, the profile area of fireproofing to 34 main and two intermediate plate girders. girders, and the deck plating panels. The correlated . can be unpropped during construction and columns and beams is approximately equal The deck configuration is completed with bulkhead 'flanges' are formed by compact 'I' only act compositely under live load. Since to the gross floor area of the steel building. Configuration of the TLP deck edge girders running along the column lines, section chords at the web plate extremities. CP117 requires elastic working load design Economics of steel buildings The use of box girder technology can be a central girder to reduce differential Both deck plating and bulkhead girder webs as well as an ultimate load check with 0.9 x The following general conclusions can be seen most clearly in the form and behaviour deflections, and three shorter girders to use stiffened plate construction. The yield stress in the extreme fibres of the drawn about the economics of steel-framed of an integrated deck structure. The design provide full perimeter support for the well integrated deck structure is shown in Fig. 6. beam, there is often no significant penalty in compared with concrete buildings in the this approach. Sometimes, however, it is local market. found that temporary propping under dead (a) For low and medium rise buildings, a load is desirable. steel structure costs about 50% more than a To achieve composite action efficiently, it is conventional concrete structure. desirable to weld the shear studs through (b) Depending on the site conditions, this Wf.tlhrr ilrfk the metal deck. This enables the deck to be penalty can be significantly reduced by the laid in long lengths over the beams without saving in foundation costs due to the lighter interference and saves considerable time in steel structure. Crane pedestals laying out the deck. Fixing the studs in the (c) The overall penalty on total capital cost shop would require holes to be located for the steel structure is between 5% and Derrick skid appropriately in the decking before laying, or i.iils 10%. When allowance is made for the alternatively require shorter deck lengths Fig. 7 11 Wellington Road, Parktown. effects of the more rapid construction with loss of continuity in structural action. Architects: Design Collaborative programme on the time-dependent costs Composite metal deck such as escalation and finance charges There are several benefits of using a metal during the construction, this penalty is deck compositely with the concrete topping. particularly so because of the desirability of virtually eliminated. The deck can be laid rapidly immediately limiting overall floor depth and using locally (d) It has been demonstrated that steel after steel erection to provide a safe working available sections of limited depth even for buildings can be completed more quickly platform and serve as a permanent shutter the longer spans to avoid the cost of built-up than conventional concrete buildings in for the concrete topping without propping. sections. In these cases Grade 50 steel used South Africa, and savings of between three Deck The correct choice of deck section can at reduced stresses can still show a cost and six months have been found for low to bulkheads minimize dead load and reinforcement while advantage. medium rise projects. However, the success providing adequate fire rating without the It should be noted that the use of Grade 50 of the project is entirely dependent on good underside having to be sprayed. Power Mating |oint steel can increase the required lead times management and on all the parties involved i Lower chord floated finishes eliminate the need for a Mezzanine deck because of problems of availability. meeting their commitments. The financial screed over the topping. Fire protection risk if the project is delayed is greater for a The range of available deck sections is Main deck' In South Africa two to four-hour rating will steel structure. Fig. 4 limited. Wider rig sections have now been generally be required for columns and (e) If a steel building is chosen it is Pontoon section being lifted Fig. 6 developed to assist with shear transmission primary beams and a two-hour rating for essential that the total architectural, into position during assembly at The deck structure of the TLP under composite action when the ribs run secondary beams and the floor. structural and services design should take Hutton TLP lower hull at Nigg across the beam, as it is normal for most advantage of the particular properties of secondary beams on a typical floor. With the This can be achieved locally by the following steel as a construction medium. A steel narrower ribs generally available locally the methods: building requires more disciplined decision• shear capacity of the studs is significantly (a) Concrete encasement - minimum of 50 making by the design team in the early reduced. mm all round. This is only practically stages if the programme advantages are to feasible for columns, and even then it is a High tensile steel be realized. tedious operation. For a high-rise building it The cost benefits of Grade 50 steel over can provide the advantage of reducing cost (f) The decision as to whether to use steei Grade 43 both in tension and compression through composite action. or concrete is a marginal one, which will be are obvious. affected by the particular circumstances (b) Spraying or plastering with vermiculite For columns, the advantages are significant. prevailing at the time. Most important is the or pearlite compositions. Thicknesses re• Up to about 10 floors, all columns can be in assessed market advantage of having the quired vary from 25mm for a two hour rating Grade 50. However, if a concrete core is building completed earlier and the financial to 40mm for four hours. used, the differential axial shortening benefit of earlier revenue and possibly between core and columns can be of the (c) Spraying with mineral fibre/ cemen- meeting a particular projected market de• titious compositions r order of 25mm for 10 floors. Above 10 to 15 mand. floors it becomes necessary to limit these (d) Fixing precast fire proof panels to the (g) The effect of using steel for these deflections by limiting the stress in the member. It is difficult to provide a fixing buildings has been to encourage contractors columns, either by using Grade 43 steel or method with the required fire rating. to find means of building faster in concrete. composite columns. Precautions of building Prefabricated systems of fire protection are A current major project, involving 20 floors of out' the dead load differentials can also be 2 in common use overseas but only one about 2000 m is being constructed using Fig. 5 Fig. 7 used. system has been satisfactorily tested locally. flat slabs and table forms at an average rate Hutton TLP column under assembly at Nigg. Foundation template units on barge Grade 50 steel also has cost benefit for The most commonly used methods to date of four to six days per floor. This has all the Outer shell about to be lifted over inner shell to form at Invergordon awaiting final shipment beams, but again deflections often govern, have been the sprayed or plastered time advantages of steel with significantly splash zone double skin 'damage control' section to Hutton TLP site, for installation 20 making mild steel more desirable. This is vermiculite or pearlite compositions. Never• less cost penalty. lead time required to procure and fabricate The composite floor is formed by flat-soffit transition structure which forms the ground the steel. trough-profile decking spanning up to 2.2m and first floors. The annexe is linked to the (b) The slid core automatically incor• with mesh reinforcement, and provides a Carlton Hotel by a skybridge across the porated the hoisting and access require• two-hour fire rating. The beams and columns Kruis Street at first floor level and a service ments for later construction of the floors, are protected by plastering with Rocklite tunnel 15m below the street. including the tower crane, personnel hoist pearlite plaster. In this case stability is Piling commenced on site in March. 1981, and stairs. Metal pan stairs provided the provided by steel bracing in certain bays. and steel erection was completed mid- essential early access to the floors. An interesting aspect of this project was the August. The building was opened in June, (c) Because many of the services such as significant saving in piled foundation cost 1982. due to the saving of 40% in mass compared toilets, stairs, plumbing, ducts and lifts are The site is very small and congested and this with a concrete structure. located in the core, work in the finishing of contributed to the decision to use steel. these could proceed immediately, unrelated warden Plaza Stand 547, Parktown to the critical path for the general floor This is a 12-storey steel-framed office This is a four-storey office building in areas. building recently completed in Johannes• Parktown. (d) Work on and in the lift motor room could burg. The typical floor layout is shown in Fig. Of the group of steel structures under Figs. 8-10 start earlier. 3. The two-level basement was constructed discussion this is the only building which Hutton TLP integrated deck under • in reinforced concrete. The main core and Once steel erection had started at ground has exposed steelwork as an architectural construction at Ardersier, Scotland. r two end stair wells were slipformed in rein• level, the structural frame was erected in feature. To achieve this the fire authorities Fig. 10 shows internal area partially forced concrete. A time saving of five three months (1'/« floors per week) and the required the building to have sprinklers fitted out with bulkhead girders in months over a concrete solution was building was completed for handover within internally and the window walls to be background (perimeter of area shown) projected. 12 months. A floor finishing cycle time of one covered internally by a fire activated water (Figs. 8-9 photos: S. Lewandowski, week per floor was achieved for each of the Bulk excavation and piling commenced on curtain. all other photos: Nick Prescott) follow-up trades. site at the beginning of 1981 and steel Design considerations erection was complete in August. The • The steel solution showed a time saving of A few design-related aspects are dealt with building was substantially complete in April, This form of construction fits the layout of five months over an equivalent concrete below in relation to solutions which have • M*. 1982. the process and services by providing a structure. Economic comparisions indicated proved efficient and economical locally. number of discrete compartments for each r that the additional capital cost of the steel A sprayed mineral fibre fire protection of the functional areas. In general terms the frame was more than off-set by reduced application developed in Canada was high risk, low manned functions occupy the interest and escalation during construction applied by a local sub-contractor, under areas at the well bay end of the platform, and and the benefits of earlier revenue. guidance from the Canadian supplier. This provided a significant improvement in the low risk, high manned functions the \ Dennehof Park application rate over what had been other end. In order to minimize the danger of This development, which comprises three available locally. A purpose-designed ribbed a manifold area explosion affecting 5* 4-storey office blocks of approximately 2 metal deck roll by G. Vincent has been used. processes or services, the well bay area is 1000m per floor, was recently completed in The depth of the deck is 90mm and the provided with an open side. This is achieved Sandton. The decision to use structural overall finished floor thickness is 160mm. by making up some sections of bulkhead steelwork was taken to minimize con• With supplementary reinforcement this girder in truss form. In order to ensure that struction time, assist in pegging escalation provides a two-hour fire rating. an explosion in the process area would not and meet a projected demand in the letting threaten the service areas the partitioning Additionally, intercostal stiffeners would be welds to flange edges (or within 6mm), and market. Analysis of the construction pro• Carlton Hotel Annexe bulkhead girder webs must resist lateral made fully continuous rather than having avoidance of the use of doubler plates gramme showed a three-month saving over a This building comprises nine hotel floors of pressure loading more readily than the deck sniped flanges as elsewhere. The hole itself (which are commonly used for pipe and would have rounded corners and a bolted service supports). concrete solution. The target programme 450m2 each constructed using a structural Figs. 5-6 plating. The heart of the deck, the control was met on site. room, is not only placed as far away from the window frame to provide the gas-tight Another item which strongly influences steel frame on top of a reinforced concrete Garden Plaza. Architects: Louis Karol high risk areas as possible, but is also given connection for the pipe or duct sleeve or structural detailing is related to the full fire protection. cable box. possibility of minor wave crest impacts on Structural behaviour of the TLP deck The deck sections do not have the same the underside of the deck for certain extreme The whole TLP design has to be a weight problems with penetrations. These are wave events. This results in the requirement 8 8 8 8 8 8 8 8 8 < control exercise. The connections of the formed by shallow plate girders, typically for extensive tripping supports to the main in m un m in in m in in deck to the hull column tops must distribute 1.2m deep with 4m centre spacing, with deck pallet girders. It also places severe stiffened plate panels spanning between constraints on exposed service ducts the load throughout the column wall shell. To Slid concrete core achieve this the deck is set down on inter• them. Inside the deck these are conceived as running between the deck and the hull connected jacks at each column top at the pallets on which equipment could be placed, column tops. time of deck to hull mating. This ensures and loose flange connected with full access The concept of a TLP integrated deck that the dead load is equally and on four sides. The pallets can then be lifted requires the high standard of fabrication determinately distributed around the column into the appropriate slot in the girder matrix finish normally associated with box girder shell. It also ensures that the deck starts life and connected using infill plates. plated structures. However, the bridge-type simply supported between two lines of The overall concept of the deck is based on top deck fatigue sensitive finish is required columns. The result is efficient use of the the maximum outfitting on a pallet before throughout in order to ensure maintenance- deck structure since the deck plating will be placement in the deck, and then the free service. The equivalent to closing down acting with the girders most effectively at maximum outfitting of the deck at low level the outer road lanes for an extended repair Slid concrete core concrete centre span, and least effectively at the on dry land. Once outfitted, the deck can be on a bridge would be shutting down the ends. The final connection is made by loaded out on to a barge and then set down whole platform - not only would this result welding infill steel between columns and on the hull column tops. in lost production with the possibility of a deck to give full moment and torsioned financial crisis for the oil company Deck structural detailing continuity. Thus the design of the deck is concerned, but in certain cases it could be dominated by fatigue near to the column The stiffness of the deck in relation to the extremely difficult to start up again. Concrete topping tops, whilst static loads are more important stiffness of the pontoons leads to certain midspan. fatigue design problems. The hull pontoons, References Shear connectors lacking any plan bracing, tend to warp a little (1) ELLIS, N. ef a/. Hutton TLP vessel struc• Of particular difficulty in design is the under a splitting wave. Since this wave is of tural configuration and design features. requirement for service and process pene• considerably shorter wavelength than the 160 (Paper OTC 4427) Proceedings 14th trations through bulkhead girders at static peak stress waves, it falls into the top :_ . Annual Offshore Technology Conference, : positions chosen by equipment layout, as end of the fatigue damage waves. The Houston, 1982. opposed to structural logic. Special warping imposes a torque load on the penetration details must be developed. columns which are effectively built in at deck (2) DET NORSKE VERITAS. Rules for design Since the size of even the largest door level. Thus the torque is carried out by the and construction of offshore structures. Beams and columns opening causes local, rather than global, lower level deck plating, the main deck DnV, 1977. fire-proofed with Secondary beam A/D type sprayed stress redistribution in the girders, pallets. As a result a considerable proportion (3) BRITISH STANDARDS INSTITUTION. BS fibre fire proofing Main beam penetrations detailing concentrates on the of the deck must be detailed extremely 5400: Part 10 1980. Steel, concrete and redistribution of load around the 'ineffective carefully, with items such as pipe supports composite bridges: code of practice for panel'. and vessels bases positioned exactly. fatigue. BSI, 1980. In general terms many details must be The bulkhead webs are stiffened primarily in (4) SMITH, I.J. ef al. Assessment of fracture adopted universally to ensure that there is a the vertical direction and secondarily, toughness requirements for the deck consistent standard of finish as regards on- intercostal stiffening is added horizontally, structure of the Hutton tension leg site inspection. Examples of this include giving rectangular unstiffened panels. platform using finite elements and the extensive use of 'softening brackets' to Around a penetration the margin stiffening CTOD design curve. (Paper OTC 4430). Fig. 4 reduce stress concentrations, a total ban on would be increased to redistribute the loads Proceedings 14th Annual Offshore Tech• Garden Plaza, typical floor, steel layout and details unnecessary stiffener details involving 14 throughout all the adjacent panels. nology Conference, Houston, 1982. It is an 18-storey office building in Johannes• Multi-storey burg, providing about 17,000m2 of office The Central accommodation over a three-level parking steel-framed basement. The layout of the typical floor Electricity \ steel frame is shown in Fig. 2. buildings in Composite action was utilized for both main Workshops, and secondary beams. The composite floor / South Africa was formed by a ribbed metal deck specially Johannesburg ; rolled for the project. A fire test carried out v / N Cliff McMillan by the South Africa Bureau of Standards Barrie Williams V confirmed that, with light reinforcement in the topping, the composite section qualified Architects: Rhodes-Harrison Fee & Bold for a two-hour fire rating on a span of 3.05m <8> V • without treatment of the underside. General description of project • The beams were sprayed with a vermiculite/ The complex is a multi-function repair and Introduction gypsum cement composite to achieve a two- workshop facility for the City Electrical Over the last 10 years our practice in South hour rating for secondary beams and three Engineer of Johannesburg on a 16 ha - Africa has had the opportunity to be involved development located on the site of the now 0 hours for main beams. The columns were -1 in the design of six multi-storey building encased in concrete to achieve composite redundant Robinson Deep mine just to the projects using steel-framed solutions. south of Johannesburg. It comprises main• / action, and at the same time provide the / Traditionally, building construction in South tenance workshops and service facilities for - required three-hour rating. • Africa has been in reinforced concrete and The central service core of the building was the generating and distribution branches, / • this remains the main medium and normally specialized test and laboratory facilities, 7 slipformed in reinforced concrete. A shows significant cost savings over vehicle workshops, comprehensive stores concrete core proved economical and structural steelwork, except for the obvious and an administration centre. structurally necessary in order to provide applications such as light roofs and In addition to being structural engineers on adequate stability and limit horizontal sway industrial buildings. However, with rising the project, Ove Arup and Partners also Fig. 1 under wind loads. The slipformed solution rates of escalation and high financing costs provided civil and mechanical engineering Master site plan had many construction advantages: during construction, there has been pressure skills and therefore played a strong role in (a) The slipforming was extremely rapid, to speed up construction and ensure earlier the site planning and co-ordination of site taking less than three months, including the occupation. In certain cases structural steel services. Road access was critical as a has shown benefits in meeting these time necessary to set up the slide, for 96-wheeled, 70m long, low loader, carrying objectives. construction from foundations to the top. 150 tonne transformers, had to be Sliding could commence immediately the accommodated and this vehicle also had an This paper describes some of the projects of core foundations had been completed and influence on the siting of the various this kind with which we have been involved. processed simultaneously with the buildings and their relationship to one Penmor Tower basement construction. Structural steel another. A further important planning and This was the first example and was really the erection could then commence off a design parameter was the requirement that E3 first multi-storey building in South Africa completed ground floor slab. The alternative the buildings should have a useful service - which incorporated the techniques of providing steel columns through the life of up to 100 years. Apart from making commonly used in Europe and North basement would have added cost with no substantial provision for future extension, America for the specific purpose of building Fig. 1 Penmor Tower. Architects: Nurcombe saving in time. The basement and core the design also had to anticipate economically and quickly in steel. Summerley Ringrose & Todd construction were able to proceed during the technological change in municipal functions and plan for a possible metropolitan servicing centre. Built up steel columns Details of the adopted Master Site Plan are shown on Fig. 1. Structural form A general interpretation of the client's requirements suggested workshop areas -Secondary * Primary plate with large column-free spaces serviced by girder castellated beam full crane facilities. Primary An important consideration was the need to beam offer the client a flexible working space with regard to usage and machine layout and at Secondary r- the same time recognize the need to adapt SOT r beam Concrete core the buildings if a change in use or » technology required it. This, together with the clearances required below crane hooks TJ|PL to assemble and transport the items of I — equipment along the length of buildings by leap frogging over the work space rather Fig. 2 than having clear access corridors, Section through new workshop complex suggested a single-storey high bay structure. The structural form also evolved from the need to make the best use of the for crane use but is more appropriate to the economics of various types of framing excellent natural light we have on the jobbing as against the production type alternatives such as lattice trusses, solid 5 100 5 100 5 100 5 100 5 100 5 100 5 100 5 100 Highveld, the need to reduce maintenance workshop. web and castellated portal frames in conjunction with the prime consideration to 775 775 and cleaning to a minimum and with due The interrelationship between building 1 335 9670 9 275 9 670 1 335 regard to developing a consistent architec• frame, the crane and its support structures retain a roof profile that would provide a n tural expression for the buildings on the site. was investigated in detail to determine the uniform and sufficient level of natural Steelwork was a natural choice for the benefits of the various alternatives and lighting. r Concrete topping structures of the main buildings and a resulted in the decision to design the main The results of these analyses clearly showed -Steel decking Concrete topping Shear connectors number of alternative schemes were building columns independently of crane that lattice trusses were the most economic — Shear connector Steel decking Mesh produced in which various roof profiles and columns where cranes were not required solution suited to the monitor profile with its Mesh framing alternatives were investigated in immediately. However, where appropriate, all beneficial natural lighting characteristics. 100* relation to natural lighting levels. foundations were designed and constructed The remaining structural components have The clear span (45m) chosen for building C5, with provision for future cranes. solid webs (girders) or solid box sections for example, was the result of studies which Beams and columns The economics of the spacing of the main (columns) as, apart from the structural re• indicated that fewer columns and less fire-proofed with Secondary beam frames was evaluated for each building in quirements, the appearance and main• perimeter cladding and a single-span protective plaster - Primary beam relation to crane girder, girt, and frame tenance qualities are more desirable and are Beams fire-proofed Secondary beam building and crane were more economical costs. It was determined that a spacing of expressed in the architecture. with sprayed vermiculite and functional than a double span with gypsum cement 9m seemed the most practical and suited the Each of the main workshop areas is served Primary beam duplication of cranes and supporting monitor spacing on the larger workshops. A by adjacent single-storey ancillary adminis• structure. This solution would not of course 9m x 9m planning grid was therefore tration, training and amenity facilities. In Fig. 2 Fig. 3 apply where long line processes have to be established for the whole site. general, these have been constructed with Penmor Tower, typical floor, steel layout and details Dennehof Park, typical floor, steel layout and details covered and where there is a high demand The schemework also investigated the reinforced concrete frames. Structural details Schedule of building data The following are details of the six main Height Total Mass steel-framed buildings of interest. to eaves Span Area steel kg/ EOT [HI • Building C1: 2 Building m m m mass tonne m2 cranes a General Test (air-conditioned, dust-free) and Heavy Equipment Store containing two C1 15 18 3230 360 111 2 x 10T 10 tonne EOT cranes. Building C3: C3 20 18 1340 300 223.9 1 x 150/25T •I III i I i a Transformer Test and Repair Building having one 150 tonne crane with 25 tonne C5 16 45 3936 337 85.6 1 x 30/5T ij auxiliary hoist. Building C5: D1 7 36 3960 185* 46.7 - a Heavy Machine Shop with 30 tonne x 45m span EOT crane. E 9.5 9+18 3 x 2T Building D1: + 36 5783 730* 68.3 Hoists Vehicle Maintenance Workshop F 9.5 9 + 18 Building E: 6 City Treasurer's Stores + 36 5824 371* 63.7 1 x 15T Building F: Carpenters' and Black Trades' Workshop "Includes steel framing for extensive mezzanine floors

Figs. 3-6 Structural design or guidelines on this for general distribution delay. Perhaps we should have anticipated Central Electricity Workshops, Johannesburg For the various loading conditions the main would be appropriate. On occasion we were this. Aspects of the new complex frames were analyzed using STRESS. The also asked to assess proposed welding Minor lack of fit full range of locally available structural procedures - another area where our Occasionally the main truss shoe sections were used including built-up box inspection staff could do with assistance. connection to the face of the box column section columns, rectangular hollow Side sway damage to glass gables was slightly skew ± 2mm gaps on one sections (fabricated) and tubes for the An interesting and highly successful feature side. This problem only becomes apparent trusses for economy, minimum light of the south gables to the main workshops is once we have access at roof level, i.e. too interference and dust collection, hot rolled the glass walls covering the full extent of the late to take corrective action on the ground. • universal sections for internal columns and buildings. The main frame side sway due to The solution we adopted was to ease off the beams and cold rolled sections for roof crane surge (40mm) caused great concern bolts of the connection and to install a purlins. among the patent glazing manufacturers, all suitable combination of 1mm and 0.5mm Areas of concern in the design were: of whom unanimously said it cannot be shims before retightening the bolts; a r—^ Temperature effects on stiff cladding and done. On examination one locally available somewhat -makeshift solution but undoub• 4 rigid fasteners system (UK design) appeared to have very tedly better than leaving the joint open. In anticipation of a requirement for improved flexible glazing bar fixing details using Sagging purlins internal environmental standards in future single swivel bolts and sliding shoes. The sagging of the cold rolled purlins caused years, an insulated skin with a hard durable Reference to their UK head office received problems even though we anticipated it both inner lining of ribbed profile was selected. the same reply, i.e. that their system could by installing a sag rod system and by In all the main buildings therefore, the roof not accommodate the movement antici• insisting, in the contract documents, that the and side cladding consisted of a double pated. However, a simple test on a mock-up sheeting contractor was responsible for metal skin rigidly fastened together and to section in their works soon proved that they maintaining the purlins in the correct the support framing using the 'Top could more than accommodate the move• position, although he aggravated the Speed'system (self-tapping screws). A desk ment we were seeking. The system has been problem by placing all the sheets for one bay study suggested that longitudinal in operation now for 2Vi years without sign in one spot and by completing one slope of temperature effects may lead to serious of damage. the roof at a time, i.e. the forces on the sag distortion of the cladding and/or failure of Minimum plate thickness in box columns rod system were not balanced. The space the fasteners. We therefore initiated a required below the underside of the roof research project, undertaken by the Once the important decision had been taken to use box section columns expressed sheeting to permit installation of the Witwatersrand University, in which the insulation and inner metal skin meant that longitudinal racking action of the side externally, the final design (stress and inertia wise) required relatively thin plates in the the sag rods were not placed in the ideal panels below the crane girder was position, i.e. close to the purlin top flange. In simulated. This confirmed the likelihood of webs for the column proportions chosen. With the fully welded up section complete the end the sheeting contractor solved the cladding failure at peripheral fasteners and problem by installing a supplementary sag proved our concern was justified. To avoid with welded internal stiffeners, we were very concerned about the visual acceptability of rod system of thin straps or ties connecting the problem the panel support framing was both top and bottom purlin flanges. The designed having suitably slotted holes and any 'tin canning' due to welding distortion. We solved this more by intuition than by lower of these remains visible - a not shoulder bolts, etc., at all connections to the altogether satisfactory solution. Our current columns, and the cladding given sufficient design by keeping plate thicknesses to a minimum of 8mm. Even so the effects are solution is to use sag rods having a certain freedom by using flashings around the amount of bending stiffness e.g. light tubes, periphery of each panel. visible if you care to look for them but we have had no serious adverse comments. with a double-bolted vertical end plate. This seems to work well. Welding and quality assurance Construction problems We were particularly concerned about Conclusion achieving first class welds in several areas Welding quality To date two phases involving 2100 tonnes of but more especially in the butt welds in As mentioned previously, welding quality structural steel have been constructed and tension members (particularly where hollow was initially a big headache with initial work has started on a third. tubes were concerned) and in the full rejection rates of 50 to 60% of key welds, i.e. We believe the project has been an all-round penetration web to flange welds of the crane truss tie butt welds and crane girder web to success that will cater for the client's needs, girders. We therefore wrote into the contract flange welds. The gamma radiation and give him flexibility and keep pace with documents that the steelwork contractor ultrasonic tests of the independent QA industrial building progress well into the 21st it would appoint an 'approved' independent programme avoided all the potential emotion century. It is interesting to note that the testing agency to give us the quality (for us that is) and ensured that we had the assurance we required. In the second phase quality required. Without continuous capital cost of the buildings compares of the project this proved to be even more of inspection and sealed name tags with extremely favourably with the analyzed a safeguard than we anticipated as, due to photographs, it proved difficult to ensure costs of similar large scale complexes initial delays in shop drawing preparation that only the correctly coded welders worked constructed for the South African Transport and manufacture, much of the work had to on our project. Services. There is no doubt that value in use arising from the selection of appropriate be sub-let to four or five other fabricators, The need for an experienced plumber structural solutions and materials will be of some of whose experience was less than The welded up box section columns each great benefit to the client. desirable. Even coding of welders was often contained a 150 0 galvanized steel downpipe. Credits a problem. To get these installed and pressure tested There should be no doubt that in these cir• before closing up the columns, required the Architects and principal agents: cumstances a quality assurance programme services of an experienced plumber. All the Rhodes-Harrison Fee and Bold is absolutely essential and can be relatively workshops tried at first to do this work Quantity surveyors: 16 inexpensive. Perhaps some technical notes themselves, at great expense, and with much Roos and Roos Inc. Structural details Schedule of building data The following are details of the six main Height Total Mass steel-framed buildings of interest. to eaves Span Area steel kg/ EOT [HI • Building C1: 2 Building m m m mass tonne m2 cranes a General Test (air-conditioned, dust-free) and Heavy Equipment Store containing two C1 15 18 3230 360 111 2 x 10T 10 tonne EOT cranes. Building C3: C3 20 18 1340 300 223.9 1 x 150/25T •I III i I i a Transformer Test and Repair Building having one 150 tonne crane with 25 tonne C5 16 45 3936 337 85.6 1 x 30/5T ij auxiliary hoist. Building C5: D1 7 36 3960 185* 46.7 - a Heavy Machine Shop with 30 tonne x 45m span EOT crane. E 9.5 9+18 3 x 2T Building D1: + 36 5783 730* 68.3 Hoists Vehicle Maintenance Workshop F 9.5 9 + 18 Building E: 6 City Treasurer's Stores + 36 5824 371* 63.7 1 x 15T Building F: Carpenters' and Black Trades' Workshop "Includes steel framing for extensive mezzanine floors

Figs. 3-6 Structural design or guidelines on this for general distribution delay. Perhaps we should have anticipated Central Electricity Workshops, Johannesburg For the various loading conditions the main would be appropriate. On occasion we were this. Aspects of the new complex frames were analyzed using STRESS. The also asked to assess proposed welding Minor lack of fit full range of locally available structural procedures - another area where our Occasionally the main truss shoe sections were used including built-up box inspection staff could do with assistance. connection to the face of the box column section columns, rectangular hollow Side sway damage to glass gables was slightly skew ± 2mm gaps on one sections (fabricated) and tubes for the An interesting and highly successful feature side. This problem only becomes apparent trusses for economy, minimum light of the south gables to the main workshops is once we have access at roof level, i.e. too interference and dust collection, hot rolled the glass walls covering the full extent of the late to take corrective action on the ground. • universal sections for internal columns and buildings. The main frame side sway due to The solution we adopted was to ease off the beams and cold rolled sections for roof crane surge (40mm) caused great concern bolts of the connection and to install a purlins. among the patent glazing manufacturers, all suitable combination of 1mm and 0.5mm Areas of concern in the design were: of whom unanimously said it cannot be shims before retightening the bolts; a r—^ Temperature effects on stiff cladding and done. On examination one locally available somewhat -makeshift solution but undoub• 4 rigid fasteners system (UK design) appeared to have very tedly better than leaving the joint open. In anticipation of a requirement for improved flexible glazing bar fixing details using Sagging purlins internal environmental standards in future single swivel bolts and sliding shoes. The sagging of the cold rolled purlins caused years, an insulated skin with a hard durable Reference to their UK head office received problems even though we anticipated it both inner lining of ribbed profile was selected. the same reply, i.e. that their system could by installing a sag rod system and by In all the main buildings therefore, the roof not accommodate the movement antici• insisting, in the contract documents, that the and side cladding consisted of a double pated. However, a simple test on a mock-up sheeting contractor was responsible for metal skin rigidly fastened together and to section in their works soon proved that they maintaining the purlins in the correct the support framing using the 'Top could more than accommodate the move• position, although he aggravated the Speed'system (self-tapping screws). A desk ment we were seeking. The system has been problem by placing all the sheets for one bay study suggested that longitudinal in operation now for 2Vi years without sign in one spot and by completing one slope of temperature effects may lead to serious of damage. the roof at a time, i.e. the forces on the sag distortion of the cladding and/or failure of Minimum plate thickness in box columns rod system were not balanced. The space the fasteners. We therefore initiated a required below the underside of the roof research project, undertaken by the Once the important decision had been taken to use box section columns expressed sheeting to permit installation of the Witwatersrand University, in which the insulation and inner metal skin meant that longitudinal racking action of the side externally, the final design (stress and inertia wise) required relatively thin plates in the the sag rods were not placed in the ideal panels below the crane girder was position, i.e. close to the purlin top flange. In simulated. This confirmed the likelihood of webs for the column proportions chosen. With the fully welded up section complete the end the sheeting contractor solved the cladding failure at peripheral fasteners and problem by installing a supplementary sag proved our concern was justified. To avoid with welded internal stiffeners, we were very concerned about the visual acceptability of rod system of thin straps or ties connecting the problem the panel support framing was both top and bottom purlin flanges. The designed having suitably slotted holes and any 'tin canning' due to welding distortion. We solved this more by intuition than by lower of these remains visible - a not shoulder bolts, etc., at all connections to the altogether satisfactory solution. Our current columns, and the cladding given sufficient design by keeping plate thicknesses to a minimum of 8mm. Even so the effects are solution is to use sag rods having a certain freedom by using flashings around the amount of bending stiffness e.g. light tubes, periphery of each panel. visible if you care to look for them but we have had no serious adverse comments. with a double-bolted vertical end plate. This seems to work well. Welding and quality assurance Construction problems We were particularly concerned about Conclusion achieving first class welds in several areas Welding quality To date two phases involving 2100 tonnes of but more especially in the butt welds in As mentioned previously, welding quality structural steel have been constructed and tension members (particularly where hollow was initially a big headache with initial work has started on a third. tubes were concerned) and in the full rejection rates of 50 to 60% of key welds, i.e. We believe the project has been an all-round penetration web to flange welds of the crane truss tie butt welds and crane girder web to success that will cater for the client's needs, girders. We therefore wrote into the contract flange welds. The gamma radiation and give him flexibility and keep pace with documents that the steelwork contractor ultrasonic tests of the independent QA industrial building progress well into the 21st it would appoint an 'approved' independent programme avoided all the potential emotion century. It is interesting to note that the testing agency to give us the quality (for us that is) and ensured that we had the assurance we required. In the second phase quality required. Without continuous capital cost of the buildings compares of the project this proved to be even more of inspection and sealed name tags with extremely favourably with the analyzed a safeguard than we anticipated as, due to photographs, it proved difficult to ensure costs of similar large scale complexes initial delays in shop drawing preparation that only the correctly coded welders worked constructed for the South African Transport and manufacture, much of the work had to on our project. Services. There is no doubt that value in use arising from the selection of appropriate be sub-let to four or five other fabricators, The need for an experienced plumber structural solutions and materials will be of some of whose experience was less than The welded up box section columns each great benefit to the client. desirable. Even coding of welders was often contained a 150 0 galvanized steel downpipe. Credits a problem. To get these installed and pressure tested There should be no doubt that in these cir• before closing up the columns, required the Architects and principal agents: cumstances a quality assurance programme services of an experienced plumber. All the Rhodes-Harrison Fee and Bold is absolutely essential and can be relatively workshops tried at first to do this work Quantity surveyors: 16 inexpensive. Perhaps some technical notes themselves, at great expense, and with much Roos and Roos Inc. It is an 18-storey office building in Johannes• Multi-storey burg, providing about 17,000m2 of office The Central accommodation over a three-level parking steel-framed basement. The layout of the typical floor Electricity \ steel frame is shown in Fig. 2. buildings in Composite action was utilized for both main Workshops, and secondary beams. The composite floor / South Africa was formed by a ribbed metal deck specially Johannesburg ; rolled for the project. A fire test carried out v / N Cliff McMillan by the South Africa Bureau of Standards Barrie Williams V confirmed that, with light reinforcement in the topping, the composite section qualified Architects: Rhodes-Harrison Fee & Bold for a two-hour fire rating on a span of 3.05m <8> V • without treatment of the underside. General description of project • The beams were sprayed with a vermiculite/ The complex is a multi-function repair and Introduction gypsum cement composite to achieve a two- workshop facility for the City Electrical Over the last 10 years our practice in South hour rating for secondary beams and three Engineer of Johannesburg on a 16 ha - Africa has had the opportunity to be involved development located on the site of the now 0 hours for main beams. The columns were -1 in the design of six multi-storey building encased in concrete to achieve composite redundant Robinson Deep mine just to the projects using steel-framed solutions. south of Johannesburg. It comprises main• / action, and at the same time provide the / Traditionally, building construction in South tenance workshops and service facilities for - required three-hour rating. • Africa has been in reinforced concrete and The central service core of the building was the generating and distribution branches, / • this remains the main medium and normally specialized test and laboratory facilities, 7 slipformed in reinforced concrete. A shows significant cost savings over vehicle workshops, comprehensive stores concrete core proved economical and structural steelwork, except for the obvious and an administration centre. structurally necessary in order to provide applications such as light roofs and In addition to being structural engineers on adequate stability and limit horizontal sway industrial buildings. However, with rising the project, Ove Arup and Partners also Fig. 1 under wind loads. The slipformed solution rates of escalation and high financing costs provided civil and mechanical engineering Master site plan had many construction advantages: during construction, there has been pressure skills and therefore played a strong role in (a) The slipforming was extremely rapid, to speed up construction and ensure earlier the site planning and co-ordination of site taking less than three months, including the occupation. In certain cases structural steel services. Road access was critical as a has shown benefits in meeting these time necessary to set up the slide, for 96-wheeled, 70m long, low loader, carrying objectives. construction from foundations to the top. 150 tonne transformers, had to be Sliding could commence immediately the accommodated and this vehicle also had an This paper describes some of the projects of core foundations had been completed and influence on the siting of the various this kind with which we have been involved. processed simultaneously with the buildings and their relationship to one Penmor Tower basement construction. Structural steel another. A further important planning and This was the first example and was really the erection could then commence off a design parameter was the requirement that E3 first multi-storey building in South Africa completed ground floor slab. The alternative the buildings should have a useful service - which incorporated the techniques of providing steel columns through the life of up to 100 years. Apart from making commonly used in Europe and North basement would have added cost with no substantial provision for future extension, America for the specific purpose of building Fig. 1 Penmor Tower. Architects: Nurcombe saving in time. The basement and core the design also had to anticipate economically and quickly in steel. Summerley Ringrose & Todd construction were able to proceed during the technological change in municipal functions and plan for a possible metropolitan servicing centre. Built up steel columns Details of the adopted Master Site Plan are shown on Fig. 1. Structural form A general interpretation of the client's requirements suggested workshop areas -Secondary * Primary plate with large column-free spaces serviced by girder castellated beam full crane facilities. Primary An important consideration was the need to beam offer the client a flexible working space with regard to usage and machine layout and at Secondary r- the same time recognize the need to adapt SOT r beam Concrete core the buildings if a change in use or » technology required it. This, together with the clearances required below crane hooks TJ|PL to assemble and transport the items of I — equipment along the length of buildings by leap frogging over the work space rather Fig. 2 than having clear access corridors, Section through new workshop complex suggested a single-storey high bay structure. The structural form also evolved from the need to make the best use of the for crane use but is more appropriate to the economics of various types of framing excellent natural light we have on the jobbing as against the production type alternatives such as lattice trusses, solid 5 100 5 100 5 100 5 100 5 100 5 100 5 100 5 100 Highveld, the need to reduce maintenance workshop. web and castellated portal frames in conjunction with the prime consideration to 775 775 and cleaning to a minimum and with due The interrelationship between building 1 335 9670 9 275 9 670 1 335 regard to developing a consistent architec• frame, the crane and its support structures retain a roof profile that would provide a n tural expression for the buildings on the site. was investigated in detail to determine the uniform and sufficient level of natural Steelwork was a natural choice for the benefits of the various alternatives and lighting. r Concrete topping structures of the main buildings and a resulted in the decision to design the main The results of these analyses clearly showed -Steel decking Concrete topping Shear connectors number of alternative schemes were building columns independently of crane that lattice trusses were the most economic — Shear connector Steel decking Mesh produced in which various roof profiles and columns where cranes were not required solution suited to the monitor profile with its Mesh framing alternatives were investigated in immediately. However, where appropriate, all beneficial natural lighting characteristics. 100* relation to natural lighting levels. foundations were designed and constructed The remaining structural components have The clear span (45m) chosen for building C5, with provision for future cranes. solid webs (girders) or solid box sections for example, was the result of studies which Beams and columns The economics of the spacing of the main (columns) as, apart from the structural re• indicated that fewer columns and less fire-proofed with Secondary beam frames was evaluated for each building in quirements, the appearance and main• perimeter cladding and a single-span protective plaster - Primary beam relation to crane girder, girt, and frame tenance qualities are more desirable and are Beams fire-proofed Secondary beam building and crane were more economical costs. It was determined that a spacing of expressed in the architecture. with sprayed vermiculite and functional than a double span with gypsum cement 9m seemed the most practical and suited the Each of the main workshop areas is served Primary beam duplication of cranes and supporting monitor spacing on the larger workshops. A by adjacent single-storey ancillary adminis• structure. This solution would not of course 9m x 9m planning grid was therefore tration, training and amenity facilities. In Fig. 2 Fig. 3 apply where long line processes have to be established for the whole site. general, these have been constructed with Penmor Tower, typical floor, steel layout and details Dennehof Park, typical floor, steel layout and details covered and where there is a high demand The schemework also investigated the reinforced concrete frames. lead time required to procure and fabricate The composite floor is formed by flat-soffit transition structure which forms the ground the steel. trough-profile decking spanning up to 2.2m and first floors. The annexe is linked to the (b) The slid core automatically incor• with mesh reinforcement, and provides a Carlton Hotel by a skybridge across the porated the hoisting and access require• two-hour fire rating. The beams and columns Kruis Street at first floor level and a service ments for later construction of the floors, are protected by plastering with Rocklite tunnel 15m below the street. including the tower crane, personnel hoist pearlite plaster. In this case stability is Piling commenced on site in March. 1981, and stairs. Metal pan stairs provided the provided by steel bracing in certain bays. and steel erection was completed mid- essential early access to the floors. An interesting aspect of this project was the August. The building was opened in June, (c) Because many of the services such as significant saving in piled foundation cost 1982. due to the saving of 40% in mass compared toilets, stairs, plumbing, ducts and lifts are The site is very small and congested and this with a concrete structure. located in the core, work in the finishing of contributed to the decision to use steel. these could proceed immediately, unrelated warden Plaza Stand 547, Parktown to the critical path for the general floor This is a 12-storey steel-framed office This is a four-storey office building in areas. building recently completed in Johannes• Parktown. (d) Work on and in the lift motor room could burg. The typical floor layout is shown in Fig. Of the group of steel structures under Figs. 8-10 start earlier. 3. The two-level basement was constructed discussion this is the only building which Hutton TLP integrated deck under • in reinforced concrete. The main core and Once steel erection had started at ground has exposed steelwork as an architectural construction at Ardersier, Scotland. r two end stair wells were slipformed in rein• level, the structural frame was erected in feature. To achieve this the fire authorities Fig. 10 shows internal area partially forced concrete. A time saving of five three months (1'/« floors per week) and the required the building to have sprinklers fitted out with bulkhead girders in months over a concrete solution was building was completed for handover within internally and the window walls to be background (perimeter of area shown) projected. 12 months. A floor finishing cycle time of one covered internally by a fire activated water (Figs. 8-9 photos: S. Lewandowski, week per floor was achieved for each of the Bulk excavation and piling commenced on curtain. all other photos: Nick Prescott) follow-up trades. site at the beginning of 1981 and steel Design considerations erection was complete in August. The • The steel solution showed a time saving of A few design-related aspects are dealt with building was substantially complete in April, This form of construction fits the layout of five months over an equivalent concrete below in relation to solutions which have • M*. 1982. the process and services by providing a structure. Economic comparisions indicated proved efficient and economical locally. number of discrete compartments for each r that the additional capital cost of the steel A sprayed mineral fibre fire protection of the functional areas. In general terms the frame was more than off-set by reduced application developed in Canada was high risk, low manned functions occupy the interest and escalation during construction applied by a local sub-contractor, under areas at the well bay end of the platform, and and the benefits of earlier revenue. guidance from the Canadian supplier. This provided a significant improvement in the low risk, high manned functions the \ Dennehof Park application rate over what had been other end. In order to minimize the danger of This development, which comprises three available locally. A purpose-designed ribbed a manifold area explosion affecting 5* 4-storey office blocks of approximately 2 metal deck roll by G. Vincent has been used. processes or services, the well bay area is 1000m per floor, was recently completed in The depth of the deck is 90mm and the provided with an open side. This is achieved Sandton. The decision to use structural overall finished floor thickness is 160mm. by making up some sections of bulkhead steelwork was taken to minimize con• With supplementary reinforcement this girder in truss form. In order to ensure that struction time, assist in pegging escalation provides a two-hour fire rating. an explosion in the process area would not and meet a projected demand in the letting threaten the service areas the partitioning Additionally, intercostal stiffeners would be welds to flange edges (or within 6mm), and market. Analysis of the construction pro• Carlton Hotel Annexe bulkhead girder webs must resist lateral made fully continuous rather than having avoidance of the use of doubler plates gramme showed a three-month saving over a This building comprises nine hotel floors of pressure loading more readily than the deck sniped flanges as elsewhere. The hole itself (which are commonly used for pipe and would have rounded corners and a bolted service supports). concrete solution. The target programme 450m2 each constructed using a structural Figs. 5-6 plating. The heart of the deck, the control was met on site. room, is not only placed as far away from the window frame to provide the gas-tight Another item which strongly influences steel frame on top of a reinforced concrete Garden Plaza. Architects: Louis Karol high risk areas as possible, but is also given connection for the pipe or duct sleeve or structural detailing is related to the full fire protection. cable box. possibility of minor wave crest impacts on Structural behaviour of the TLP deck The deck sections do not have the same the underside of the deck for certain extreme The whole TLP design has to be a weight problems with penetrations. These are wave events. This results in the requirement 8 8 8 8 8 8 8 8 8 < control exercise. The connections of the formed by shallow plate girders, typically for extensive tripping supports to the main in m un m in in m in in deck to the hull column tops must distribute 1.2m deep with 4m centre spacing, with deck pallet girders. It also places severe stiffened plate panels spanning between constraints on exposed service ducts the load throughout the column wall shell. To Slid concrete core achieve this the deck is set down on inter• them. Inside the deck these are conceived as running between the deck and the hull connected jacks at each column top at the pallets on which equipment could be placed, column tops. time of deck to hull mating. This ensures and loose flange connected with full access The concept of a TLP integrated deck that the dead load is equally and on four sides. The pallets can then be lifted requires the high standard of fabrication determinately distributed around the column into the appropriate slot in the girder matrix finish normally associated with box girder shell. It also ensures that the deck starts life and connected using infill plates. plated structures. However, the bridge-type simply supported between two lines of The overall concept of the deck is based on top deck fatigue sensitive finish is required columns. The result is efficient use of the the maximum outfitting on a pallet before throughout in order to ensure maintenance- deck structure since the deck plating will be placement in the deck, and then the free service. The equivalent to closing down acting with the girders most effectively at maximum outfitting of the deck at low level the outer road lanes for an extended repair Slid concrete core concrete centre span, and least effectively at the on dry land. Once outfitted, the deck can be on a bridge would be shutting down the ends. The final connection is made by loaded out on to a barge and then set down whole platform - not only would this result welding infill steel between columns and on the hull column tops. in lost production with the possibility of a deck to give full moment and torsioned financial crisis for the oil company Deck structural detailing continuity. Thus the design of the deck is concerned, but in certain cases it could be dominated by fatigue near to the column The stiffness of the deck in relation to the extremely difficult to start up again. Concrete topping tops, whilst static loads are more important stiffness of the pontoons leads to certain midspan. fatigue design problems. The hull pontoons, References Shear connectors lacking any plan bracing, tend to warp a little (1) ELLIS, N. ef a/. Hutton TLP vessel struc• Of particular difficulty in design is the under a splitting wave. Since this wave is of tural configuration and design features. requirement for service and process pene• considerably shorter wavelength than the 160 (Paper OTC 4427) Proceedings 14th trations through bulkhead girders at static peak stress waves, it falls into the top :_ . Annual Offshore Technology Conference, : positions chosen by equipment layout, as end of the fatigue damage waves. The Houston, 1982. opposed to structural logic. Special warping imposes a torque load on the penetration details must be developed. columns which are effectively built in at deck (2) DET NORSKE VERITAS. Rules for design Since the size of even the largest door level. Thus the torque is carried out by the and construction of offshore structures. Beams and columns opening causes local, rather than global, lower level deck plating, the main deck DnV, 1977. fire-proofed with Secondary beam A/D type sprayed stress redistribution in the girders, pallets. As a result a considerable proportion (3) BRITISH STANDARDS INSTITUTION. BS fibre fire proofing Main beam penetrations detailing concentrates on the of the deck must be detailed extremely 5400: Part 10 1980. Steel, concrete and redistribution of load around the 'ineffective carefully, with items such as pipe supports composite bridges: code of practice for panel'. and vessels bases positioned exactly. fatigue. BSI, 1980. In general terms many details must be The bulkhead webs are stiffened primarily in (4) SMITH, I.J. ef al. Assessment of fracture adopted universally to ensure that there is a the vertical direction and secondarily, toughness requirements for the deck consistent standard of finish as regards on- intercostal stiffening is added horizontally, structure of the Hutton tension leg site inspection. Examples of this include giving rectangular unstiffened panels. platform using finite elements and the extensive use of 'softening brackets' to Around a penetration the margin stiffening CTOD design curve. (Paper OTC 4430). Fig. 4 reduce stress concentrations, a total ban on would be increased to redistribute the loads Proceedings 14th Annual Offshore Tech• Garden Plaza, typical floor, steel layout and details unnecessary stiffener details involving 14 throughout all the adjacent panels. nology Conference, Houston, 1982. Table 1: Structural costs of steel-framed buildings theless, these are time-consuming wet each set of loadings, elements can be Table 2. Typical partial stress factors(Tp). trades, and fire protection remains one of checked for the complete design condition Costs at 1980 rates: Rands/m2 the important time and cost drawbacks to for compliance with DnV rules by summing Load categories Operating Extreme Fatigue the effective use of structural steelwork for member forces in accordance with the (1/12th year) (100 year) Penmor Dennehof Garden buildings, due to the limited experience in relationship for element force: the local industry and relatively small Permanent (P) 1.3 1.0 N/A Tower Park Plaza F=2Fl7pi market. Functional (F) 1.3 1.0 N/A Cost comparisons where F, is the element force for load case i, Steel beams R 44.90 R 22.06 R 43.30 and pi is the appropriate partial stress Static Buoyancy (B ) 1.3 1.0 N/A Table 1 sets out the elemental estimating s factor. Using this approach the overall safety Shear studs 2.13 3.70 3.40 components for three typical steel office Dynamic Buoyancy (B ) 1.3 1.3 1.0 factor for the design can be expressed in the D Steel columns and bracing 19.00 structures. Changes in detail could occur - (wave generated) 13.30 15.60 form: _ , ,, for example cement mortar screeds may be Safety factor = 7 .7, y .£ m p Inertia 1.3 1.3 1.0 Steel decking 12.00 11.72 16.00 preferred in certain cases to a power floated

Concrete topping including mesh finish. However, power floating has the where Tm is the partial factor on material Tethers - due to permanent (Tp) 1.3 1.0 N/A advantage of speed and minimum weight. strength, K is the slenderness ratio and i// is and power float finishing 11.00 10.29 9.96 Tethers - due to functional/live (T ) 1.3 1.0 N/A Furthermore foundation requirements would the load redistribution factor. L Temporary propping of deck 2.50 1.72 — have to be analyzed to suit the particular In addition, the use of fracture mechanics in Tethers - due to environmental (TE) 1.3 1.3 1.0 design and site conditions and must be built the design of thick plate members enables Fire protection Environmental (E) 1.3 1.3 1.0 (Plastered or Sprayed Vermiculite) 14.00 13.16 14.42 into the cost estimate. the designer to ensure that the elements Deformation (D) Temperature, lack of fit, etc. 1.0 1.0 N/A It must also be noted that the fireproofing of prone to fatigue damage are not limited by fracture toughness resistance. This ensures R 105.53 R 75.95 R 102.68 structures by spraying demands that the Accidental (A) 1.0 N/A N/A compliance with the basic limit state perimeter of the building be clad with philosophy of preventing potential cata• temporary tarpaulins to avoid material being of the hull is closer to shipbuilding, in bay area, with its riser tensioners and drill strophic modes from dominating the design. Composite action sprayed over the neighbourhood. The rate particular to submarine hull construction derrick support rails. In the case of the present project it also The economic advantage of composite per m2 for the spray application should practice. The TLP deck spans between two The deck is an all-welded structure formed enabled fatigue assessments made with ref• action for both primary and secondary include for this requirement. As a rough lines of three columns, each using three by these main plate girders, or bulkhead erence to SS 5400 Part 10 SN curves to be beams is well-known. Normally the beams guide, the profile area of fireproofing to 34 main and two intermediate plate girders. girders, and the deck plating panels. The correlated . can be unpropped during construction and columns and beams is approximately equal The deck configuration is completed with bulkhead 'flanges' are formed by compact 'I' only act compositely under live load. Since to the gross floor area of the steel building. Configuration of the TLP deck edge girders running along the column lines, section chords at the web plate extremities. CP117 requires elastic working load design Economics of steel buildings The use of box girder technology can be a central girder to reduce differential Both deck plating and bulkhead girder webs as well as an ultimate load check with 0.9 x The following general conclusions can be seen most clearly in the form and behaviour deflections, and three shorter girders to use stiffened plate construction. The yield stress in the extreme fibres of the drawn about the economics of steel-framed of an integrated deck structure. The design provide full perimeter support for the well integrated deck structure is shown in Fig. 6. beam, there is often no significant penalty in compared with concrete buildings in the this approach. Sometimes, however, it is local market. found that temporary propping under dead (a) For low and medium rise buildings, a load is desirable. steel structure costs about 50% more than a To achieve composite action efficiently, it is conventional concrete structure. desirable to weld the shear studs through (b) Depending on the site conditions, this Wf.tlhrr ilrfk the metal deck. This enables the deck to be penalty can be significantly reduced by the laid in long lengths over the beams without saving in foundation costs due to the lighter interference and saves considerable time in steel structure. Crane pedestals laying out the deck. Fixing the studs in the (c) The overall penalty on total capital cost shop would require holes to be located for the steel structure is between 5% and Derrick skid appropriately in the decking before laying, or i.iils 10%. When allowance is made for the alternatively require shorter deck lengths Fig. 7 11 Wellington Road, Parktown. effects of the more rapid construction with loss of continuity in structural action. Architects: Design Collaborative programme on the time-dependent costs Composite metal deck such as escalation and finance charges There are several benefits of using a metal during the construction, this penalty is deck compositely with the concrete topping. particularly so because of the desirability of virtually eliminated. The deck can be laid rapidly immediately limiting overall floor depth and using locally (d) It has been demonstrated that steel after steel erection to provide a safe working available sections of limited depth even for buildings can be completed more quickly platform and serve as a permanent shutter the longer spans to avoid the cost of built-up than conventional concrete buildings in for the concrete topping without propping. sections. In these cases Grade 50 steel used South Africa, and savings of between three Deck The correct choice of deck section can at reduced stresses can still show a cost and six months have been found for low to bulkheads minimize dead load and reinforcement while advantage. medium rise projects. However, the success providing adequate fire rating without the It should be noted that the use of Grade 50 of the project is entirely dependent on good underside having to be sprayed. Power Mating |oint steel can increase the required lead times management and on all the parties involved i Lower chord floated finishes eliminate the need for a Mezzanine deck because of problems of availability. meeting their commitments. The financial screed over the topping. Fire protection risk if the project is delayed is greater for a The range of available deck sections is Main deck' In South Africa two to four-hour rating will steel structure. Fig. 4 limited. Wider rig sections have now been generally be required for columns and (e) If a steel building is chosen it is Pontoon section being lifted Fig. 6 developed to assist with shear transmission primary beams and a two-hour rating for essential that the total architectural, into position during assembly at The deck structure of the TLP under composite action when the ribs run secondary beams and the floor. structural and services design should take Hutton TLP lower hull at Nigg across the beam, as it is normal for most advantage of the particular properties of secondary beams on a typical floor. With the This can be achieved locally by the following steel as a construction medium. A steel narrower ribs generally available locally the methods: building requires more disciplined decision• shear capacity of the studs is significantly (a) Concrete encasement - minimum of 50 making by the design team in the early reduced. mm all round. This is only practically stages if the programme advantages are to feasible for columns, and even then it is a High tensile steel be realized. tedious operation. For a high-rise building it The cost benefits of Grade 50 steel over can provide the advantage of reducing cost (f) The decision as to whether to use steei Grade 43 both in tension and compression through composite action. or concrete is a marginal one, which will be are obvious. affected by the particular circumstances (b) Spraying or plastering with vermiculite For columns, the advantages are significant. prevailing at the time. Most important is the or pearlite compositions. Thicknesses re• Up to about 10 floors, all columns can be in assessed market advantage of having the quired vary from 25mm for a two hour rating Grade 50. However, if a concrete core is building completed earlier and the financial to 40mm for four hours. used, the differential axial shortening benefit of earlier revenue and possibly between core and columns can be of the (c) Spraying with mineral fibre/ cemen- meeting a particular projected market de• titious compositions r order of 25mm for 10 floors. Above 10 to 15 mand. floors it becomes necessary to limit these (d) Fixing precast fire proof panels to the (g) The effect of using steel for these deflections by limiting the stress in the member. It is difficult to provide a fixing buildings has been to encourage contractors columns, either by using Grade 43 steel or method with the required fire rating. to find means of building faster in concrete. composite columns. Precautions of building Prefabricated systems of fire protection are A current major project, involving 20 floors of out' the dead load differentials can also be 2 in common use overseas but only one about 2000 m is being constructed using Fig. 5 Fig. 7 used. system has been satisfactorily tested locally. flat slabs and table forms at an average rate Hutton TLP column under assembly at Nigg. Foundation template units on barge Grade 50 steel also has cost benefit for The most commonly used methods to date of four to six days per floor. This has all the Outer shell about to be lifted over inner shell to form at Invergordon awaiting final shipment beams, but again deflections often govern, have been the sprayed or plastered time advantages of steel with significantly splash zone double skin 'damage control' section to Hutton TLP site, for installation 20 making mild steel more desirable. This is vermiculite or pearlite compositions. Never• less cost penalty. the associated back-up services would have great for a TLP type solution. In addition, the concrete, and, although faster to erect than Almondell Footbridge is a cable-stayed The use of to be placed on the platform. overconsolidated soils of the North Sea Local reports reinforced concrete, the steel-framed struc• girder bridge of 30m span. The simple 19m plated steelwork With a tension leg platform, such as the make the tension foundations economically tures are generally 25 to 35% more expen• high 'A' frame and vierendeel deck produce a example TLP, the operational constraints are viable for intermediate water depths. The summary sive than reinforced concrete. dramatic but pleasing structure which suits in a tension leg the same as those for a conventional fixed details of the application of the TLP to the (2) SCOTLAND the heavily wooded surroundings. platform, since it must receive the same North Sea development can be found The four Arup offices of the Scottish At Kings Buildings the problem of con• elsewhere1. Jim Hannon platform design operational approval. The TLP concept uses practice: Aberdeen, Dundee, Edinburgh and structing a new boilerhouse and chimney a floating vessel, a semi-submersible type Design approach for TLP Glasgow have designed a wide variety of round the existing plant while maintaining a structure, which is connected to the sea-bed Tension leg platform design can make good The following digest is from the papers by: steel structures over the years. continuous supply of heat was neatly solved using steelwork. The cluster of eight new Nick Prescott in such a manner that the vertical tension use of the limit state approach. In the case of (1) David Bedford - Hong Kong Typical of the range are three of our projects 2 legs are kept taut by the vessel's excess the example TLP this was based on the DnV which have received Structural Steel Design steel flues is structurally independent of the (2) Derek Blackwood - Scotland existing brick chimney round which they buoyancy. The vessel configuration chosen (Det Norske Veritas) rules. Static loadings on Awards; The Royal Commonwealth Pool, were built. Introduction to the TLP for the example TLP is a simple unbraced a TLP vessel consist of permanent loadings (3) Ian Mackenzie-Australia Edinburgh, Almondell Footbridge and Kings framework in which the members are formed A fixed offshore oil or gas production (structure and equipment), functional (4) Cliff McMillan-South Africa Buildings Boilerhouse. In recent years our experience in the use of platform structure is designed to provide a from stiffened steel plate components using loadings (consumables and live loads), (5) Finbar McSweeney - Ireland The superstructure of the Royal Common• steelwork seems to have fallen roughly into safe working platform in an exposed marine stressed skin design as in a box girder buoyancy and tension leg loadings. To wealth Swimming Pool is of 280 tonnes of three broad categories: environment. On this working platform the bridge. This concept results in close ensure that equilibrium is maintained, all the for the Arup Partnerships Structural Steel• structural steelwork construction with a roof various processes associated with oil or gas structural interaction between the square work Seminar in 1982. (a) Civil engineering partial load factors (7 f) on these loads have of 78m x 68m in two way spanning steelwork. production must be carried out in all vessel base (the pontoons), the deck (which to be considered as unity and member forces (1) HONGKONG In addition to the perimeter columns, the weathers and without interruption. These contains all the plant and facilities) and the (b) Low rise buildings factored by an appropriate stress factor. This Arup involvement with steelwork in Hong planning of the interior permitted support would include the primary separation of six interacting columns (Fig. 1). stress factor (7p) should be chosen to Kong tends to be limited to specific from a single off-centre internal column. (c) Roof structures. fluids extracted, the control of their export The tension leg designs were originally put ensure compliance with the 'Ultimate limit elements of construction and the design of and the services associated with continuous forward as deep water structures for sea state' as defined in DnV Section 4. temporary works. production. They may also include the equip• depths between 1,000 and 2,000ft. However, Environmental wave and wind loadings can The local fabrication facilities are minimal, ment for the drilling and testing of the wells, the field, at 482ft. in the East Shetland Basin be treated in a similar manner with a partial apart from a few local shipyards which have and for the injection of water or gas into the area of the North Sea, is being developed stress factor (7 p) chosen to be compatible begun to diversify the field of structural field. using such a platform since the TLP has with the DnV recommendations. Table 2 steelwork construction. This means that, With major isolated installations, consider• been recognized as being cost-effective for summarizes the partial stress factors used generally, structural steelwork is fabricated ations of continuous operation would intermediate water depths. Had the process in the design of the operating, extreme, and overseas, thus requiring a long lead-in time, require the platform to be manned round the requirements been radically more complex, fatigue limit states for the Hutton TLP. and once the shipping of the fabricated clock, and hence accommodation units with the platform oayload could have become too Having carrried out analyses appropriate to sections has commenced there is little flexibility to incorporate alterations or Fig. 1 modifications. The requirement of the Building Regulations Schematic view of Hutton TLP and, below-the geometry regarding concrete encasement for cor• rosion protection, etc., and a reluctance to Table 1: Geometry (All dimensions to moulded lines) accept lightweight fire protection, until Length: Between column centres 78.00m recently, have led to all the steel-framed Overall 95.70m buildings erected to date in Hong Kong having their structure totally encased in (O } •4..'.;-.' ' V SY • «> ^ Breadth: Between column centres 74.00m Overall 91.70m Fig. 1 Almondell Footbridge Height: Keel to main deck 57.70m Main deck to weather deck 11.25m Fig. 2 The Royal Commonwealth Pool. Architects: Robert Matthew, Johnson- Draught: Operating 32.00m at LAT Marshall & Partners

Freeboard: To underside of main deck 24.50m at LAT

Water plane: Area 1324.00m2

Columns: 4 Corners 17.70m dia. 2 Centre 14.50m dia.

Pontoons: Height 10.80m Width 8.00m Corner radius 1.50m

Displacement: Approx. 61500 tonnes

Total weight: Including riser tension 48500 tonnes (Approx)

Fig. 2 Fig. 3 Hutton TLP 1.33 model under Hutton TLP tower hull under construction maximum height, maximum steepness, regular in the dry dock at Nigg. waves in NMI main test tank, London Pontoon is about to be lifted in. Some examples of each type are given below: (a) Civil engineering Most of our work in this field has been in reinforced and prestressed concrete but we have been involved in several interesting projects with structural steel elements. In conjunction with a consortium, Cale• donian Platforms Structures, we developed a design for an offshore oil production platform, Forth 150. This included a steel deck structure comprising 4,000 tonnes of grade 50D tubular steel. The firm are joint engineers with Messrs. Crouch and Hogg for the Kessock Bridge, an important cable-stayed road bridge with a main span of 240m over the Beauly Firth. We assisted by checking and approving the design of the box steel pylons and deck crossbeams in accordance with the Merrison Rules. Further north, on the stormy shoreline of Scapa Flow in the Orkney Islands, we have currently under construction three roll-on roll-off South Island Ferry Terminals in• corporating hydraulically operated hinged Fig. 3-4 steel ramps. Hangar 8, Jan Smuts Airport, South Africa. Architects: South African Railways Fig. 4 Fig. 5 (b) Low rise buildings Brent C flare tower: transportation of prefabricated sections. Arups carried Brent C flare tower: Within this, the largest category, are indus• out dynamic fatigue and analysis checks as well as being responsible for erection of tower sections trial, school and recreation buildings, mainly obtaining certification. We were also responsible for the appraisal of (Photo: courtesy of single storey, where steel comes into its lifting and temporary works. (Photo: courtesy of Sea and Land Pipelines) Sea and Land Pipelines) own, with its lightweight and speedy erection unhampered by the need for fire Figs. 6-7 protection. Fort McMurray flare stack, Canada: erection of guyed riser with riser fabricated in sections and erected in two parts. In spite of strong competition from the Designed by Ove Arup & Partners. (Photo: courtesy of Bechtel International) package dealers there remains a demand for the one-off building for which an off-the-shelf solution does not readily cater. Typical of many school and college buildings 8 we have designed is the games hall at Anderson High School, Lerwick. It is interesting to note that at this site in the Shetland Islands, the most northerly part of the UK, the design wind pressures are very high (twice those for the south of England) resulting in significantly heavier steelwork than would be required in southern parts of tive industries and power generation. The for example, a shopping mall. Bracing to the mainland. use of structural steel in building side walls or infrequent internal masonry construction is very widespread but usually walls is required for stability. (c) Roof structures on a small scale. (d) High rise office buildings While the basic structure of many of our The economic use of structural steel in the buildings is of reinforced concrete or Typically the design of structural steel within the Australian offices of Ove Arup & Partners floor systems of high rise office buildings is loadbearing masonry, steelwork still plays an falls into the following categories: heavily influenced by the speed of con• important role in roof structures where struction. It can sometimes be demonstrated lightweight is often an advantage and added (a) Industrial buildings that the use of structural steel framing and fire protection is not required. Industrial buildings for warehouse and composite metal decking can lead to a In the case of theatres, steelwork provides factory facilities are typically portal frame significantly faster typical floor construction buildings fabricated from universal beam an ideal solution where services and access cycle in high rise office buildings. The l sections. Clear eaves heights of 5 - 6m and can be provided within the structural depth consequent saving in holding charges can spans of up to 30m are common. Wind of the roof trusses. more than offset the higher construction loading is resisted by portal frame action Two theatres which we have recently cost of a steel structure. and braced panels. completed are the Dundee Repertory Theatre (e) Mining applications Prefinished metal deck roofing has largely and the Pitlochry Festival Theatre. Structural steel is commonly used for disadvantages of each of these sections Cruciform angles the tower or parts of the tower to be carried replaced the cheaper asbestos roof The Dundee Theatre is a triumph of ingenuity framing structures in the mining industry. It may not be immediately apparent and they out in the fabricator's yard prior to shipment. sheeting. This is supported on cold rolled They have the same advantages and dis• in fitting a 450-seat auditorium with all the finds applications to heavy duty structures, are summarized as follows: This avoids the situation where errors found Zed purlins. Walls may be metal cladding on advantages as equal angles. associated facilities into an extremely tight platforms, conveyor supports and de- during erection are difficult and expensive to C sections or of masonry construction. Tubular members They require complicated battening and city site. Steelwork is used in the auditorium watering bunkers. A number of commissions rectify. Also, base setting templates are used splicing details. roof, and the flytower structure which rises (b) Roofs to low rise offices and commercial have been carried out for an iron ore Lend themselves more readily to a variety of to ensure that the holding down bolts cast to 18m. buildings processing plant. plan shapes. Fabrication into the concrete foundations match the At Pitlochry, a holiday town in the Highlands Numerically these are probably the most (f) One off structures The range of sizes is greater but they may Knowledge of the fabrication process is steelwork interface. of Scotland, a slightly larger theatre common use of structural steel in each of The Melbourne office have designed 4 steel not be readily available. essential to the detailing of steelwork. It is (540-seat) has been built in rural sur• the Australian offices. An average job would floodlight towers for an athletics stadium. They require special skill in fabrication, also important when considering suitable Conclusions roundings, again using steelwork for the roof contain less than 15 tonnes of steel. They ranged up to 58m in height with the particularly for profiled connections. sub-contractors for carrying out the work as The experience we have built up over a Fire regulations generally permit buildings of the range of skills and facilities available structures. access ladders and platforms contained They are more expensive than angles, weight period of years enables us to respond up to three storeys to be of metal roof from steelwork fabricators both in the UK within the tapered tubular section. They were for weight. quickly to the demands of our clients and (3) AUSTRALIA construction. Flat roofing is adopted on cold designed for dynamic effects and fatigue and overseas is wide and varied. advise them on all aspects of the design and They are structurally more efficient and The use of structural steel within Australia is formed purlin sections supported on conditions. Fabrication drawings are normally prepared construction of tower structures. Our attract less wind load than angles. actively promoted by the Australian Institute universal beams. Mineral wool provides by the fabricator based on engineering analytical tools are sharp and we keep of Steel Construction. This organization thermal insulation. (4) SOUTH AFRICA Equal angles design drawings. It is recommended that the abreast of design development in the related fabrication drawings are checked to fields. arranges seminars, courses and lectures, (c) Shopping centres Hangar 8 - Jan Smuts Airport Best utilized for square towers. publishes journals, magazines and safe load minimize misinterpretation of the design Roofs to shopping centres are similar to The origins of this project date back to 1973 Maximum size normally available is 200mm x A large part of our work is overseas and from tables and it sponsors research as well as those described above but much larger in when South Africa Airways decided that a requirements and inspections of the time to time we have relied heavily on our 200mm. maintaining library information. area. Trusses may be substituted for new maintenance hangar able to cater for steelwork fabrication are carried out to overseas offices for local support. We have The greatest tonnage of structural steel is universal beams for the larger spans. Usually the new generation of wide-bodied jets Easy to fabricate and readily available. check for quality, workmanship and per• enjoyed their understanding and close co• used in heavy industrial works such as the they are concealed above lightweight would be required by the early '80s. At that Cheaper than tubes weight for weight. formance. operation and we hope that this working 22 petrochemical industry, energy and extrac- ceilings, unless they appear as a feature in, time, construction of a 150 x 100m hangar They attract more wind load than tubes. It is common practice for trial erections of relationship will continue. 11 Wind forces on antennas can be obtained Method of analysis dynamic effects should be considered and capable of accommodating two Boeing 747s Usually steelwork is let as a nominated sub• alternative source of supply. There is either from manufacturers' literature based Lattice tower structures are considered as they include: had just been completed. SAA, in contract. We find that this has the advantage however a price differential which has on wind tunnel tests or derived from the three dimensional space frames. Fully tri• fully welded structures where fatigue may be conjunction with a multi-disciplinary tech• of selected tendering as well as a later need inhibited more general use of continental method given in 'Calculation of wind forces angulated structures with bolted significant nical team from the South African Transport for tender information. However, there can sections. and pressures on antennas', by Cohen, connections are assumed to be pinned Services, embarked on feasibility and be difficulties in precise definition of work structures supporting TV antennas, rad• There is limited capacity for economic Vellozi and Suh. frameworks. There are small errors involved conceptual design studies. content when variations arise. On the other iators, particularly at the top fabrication of plate girders and castellated Snow and ice in this assumption such as the legs being It was decided that a hangar complex hand measurement in the Bill of Quantities, tubular members with a slenderness ratio beams. These would normally be imported continuous at the nodes but these effects comprising two major hangars with a central in spite of the apparent precision of the ready-made. Stock holders keep some Snow and ice will contribute to the gravity exceeding 180 where local cross wind are rarely structurally significant. Separate annexe located between them would best information, has not always worked well and supplies and since may jobs are modestly load on the structure but the accretion of ice effects may be significant. on individual members or antennas will checks may be carried out for bending facilitate aircraft movement and at the same selection of tenderers is less controllable. sized the necessity to buy there tends to moments arising from locally applied forces There are a number of computer programs increase the surface area and hence time minimize fire risk. It was decided that There has been a chronic problem in over increase job costs. or eccentricities at connections. For fully available for carrying out a dynamic increase the drag forces due to wind. Icing is each hangar should, if feasible, be a clear capacity in the steelwork fabrication in• Certainly where anything other than Grade welded structures or statically indeterminate analysis. In-house programs include expressed in terms of radial thickness and spanning structure of 150 x 100m so as to dustry in Ireland. There are several major 43 steel is envisaged the lead in period must structures, framing moments must be DYMAST, GLADYS, DAFT and PAFEC but some guidance is given by the Department maximize space utilization. firms who have the resources and expertise allow for mills ordering to be feasible. evaluated. only DYMAST is suitable for a random of Energy in 'Guidance of the design and Our favoured solution comprised a main to tackle any job which has yet been built in The standard facilities available to the larger stochastic analysis. construction of offshore installations'. portal spanning 150m over the doors, with the country. There is also a wide selection of firms provide all the necessary equipment There are two in-house computer programs Detailed design considerations For the icing condition a reduced wind speed available for carrying out a static analysis of three main trusses spanning 100m from the small and medium sized fabricators so that for fabrication for most situations. Design standards is considered and this is in the order of 90% these structures, TOWER and PAFEC. back wall to the portal. We proposed long- for smaller jobs there is an embarrassment Automated cutting and drilling has recently of the design wind speed depending on the Design standards may be specified in the span crane bridges in the 37.5m bays of choice. become available but is still unusual. TOWER was developed specifically for pin- locality. head contract specification according to the between trusses to handle the servicing Welding techniques nowadays almost jointed statically determinate microwave requirements. Technical standards can be variable but Temperature country of origin with reference to more universally employ semi-automatic C02 towers and includes analysis, design and excellent results are possible provided the specific internationally recognized design The main hangar structure systems, at least in the shop. Automatic Loading from climatic temperature vari• plotting facilities. The main members and job documentation and site control are good, Each hangar section consists of steel- welding is rarely done, partly on account of ations is not normally significant for these the secondary members may be specified by codes. In recent years a number of design and the tenders are based on selection. framed structure supported on three sides the scale of work involved. types of tower structures. size in which case a straightforward analysis guides and codes of practice appropriate to Likewise, management can be uneven and by braced walls and on the fourth side by a Most fabricators do not employ welding is carried out. Otherwise the program tower structures have been published. The tends to be skimped when resources are Temperature effects due to hot or cold gases pinned base portal frame of 151.2m span. performs an iterative analysis of each panel, main ones are: stretched, either technically or financially. technologists and this service combined in the risers and due to radiation from flaring The roof is divided into four equal sections of selecting from library files those member (1) BS6235:1982 with NDT interpretation is provided by one or may induce local stresses and possibly 38.8 x 100m, each of which has a suspended The potential is certainly there to achieve sizes not specified, until a satisfactory Code of practice for two freelance specialists. By and large this influence the choice of materials. system of runway beams for the support of very high standards if sufficient input is design is achieved. fixed offshore structures. arrangement is satisfactory but difficulties Waves cranes and general purpose maintenance provided and the work well supervised. (2) Department of Energy 1982 can arise where the fabricator does not Offshore structures such as towers mounted Deflections and rotations are calculated at platforms. Three main trusses span 100m realize when he is out of his depth. We tend Offshore installations: Design is normally to BS 449 and the BCSA on platforms may be required to withstand the top of the tower, at the top of each panel from the west wall to the main portal at to use radiography and ultrasonics, partly as guidance on design and construction. Handbooks are universally available. The wave loading. The effects are usually and at the level of each applied load. The 37.8m centres. normal source of materials is the UK. There psychological tools to convey the im• foundation forces are calculated at each leg {3)APIRP2A: 1982 assessed by applying an appropriate The roof structure supports the moving is a degree of continental influence and portance of workmanship as much as the of the tower and steel weights are totalled by acceleration input to the base of the tower. (American Petroleum Institute) loads from the cranes and service platforms during times of BSC strikes this forms the actual test. Generally this works quite well. member type and steel grade. Earthquakes Recommended practice for planning, as well as the necessary lighting, fire designing and construction fixed offshore Earthquake loading is rarely significant in In most cases self-supporting lattice towers protection services and the comfort heating Building types Descriptions of some individual buildings the design of towers. In seismically active are not dynamically sensitive. As a general platforms. system. Advance factories Bailey's Irish Cream factory areas the effects are considered by applying guide, structures having a fundamental (4) DnV (Det norske Veritas) The 150m span portal, with a mass of 262 Most advance factories are sponsored by the This is an 18,000m2 building which utilizes, a base acceleration obtained either from an period of oscillation less than three seconds Rules for the design, construction and tonnes, was assembled in sections on the Industrial Development Authority who share for the first time in Ireland, the 'Nodus' appropriate ground response spectrum or can be designed safely on a quasi-static inspection of offshore structures. ground, welded and then jacked up 25m into the work among many design teams. At this system on a large scale. CHS concrete-filled from a response time history. basis. There are exceptions to this where (5) Draft Code of Practice 1978: position at the top of the legs. The main level concrete competes strongly with steel columns at 19.6m each way support the Lattice towers - loading. trusses were lifted in sections on to trestle and is probably a bit cheaper currently. space frames which number 43 in all. Each supports and welded in situ. The entire Fig. 2 These documents tend to complement each Systems of two-way trusses (bolted in one was assembled at ground level and lifted structure remained supported on the trestles Jebel AM microwave tower, other in particular areas but they also refer direction) have been used but more recently into position. A 'Mero' truss portal spanning until it was completed and then a system of designed by Ove Arup & Partners to national design standards and some one-way members in alternating directions 19m is used to support the entrance canopy. jacking it down to release the supports was (Photo: Mike Shears) interpretation is often required. in adjacent bays have been found to be quite Geffy Corporation factory implemented. successful, almost equally effective, and This is a modest 2,000m2 factory notable for Strength and stability The structure is stabilized through bracing in cheaper. its unusual use of concrete block vertical Where no other design standards are given, all three walls which interact with the portal Purpose designed factories structure. However the steel is also the strength and stability of towers are most stiffness to provide stability. In-plane bracing A large diversity of structural form has been interesting, using 686 x 152mm castellated commonly assessed on the basis of the is provided in the roof. utilized to fit specific briefs. They range from universal beams (CUB) as main beams on a design approach given in BS 449. The Roof drainage is provided along valleys, portal frames to Nodus, depending on the 15m, 3 span grid and lighter CUB of the same permissible stresses incorporate factors of dimensions as secondary beams in alter• midway between the main trusses, the brief, the client's cost consciousness and Fig. 3 safety against failure in the range of 1.5 to nating orientation. Continuity of main beam ridges being over the main trusses and at the the architect's powers of persuasion. Microwave tower 1.7. As wind is a predominant loading feature over the circular hollow section columns, ends. Office buildings under construction in Nigeria, on these structures we tend not to use the using 8.8mm bolts, permitted the use of A feature of the structure is the neatness of Since office buildings really got going about designed by Ove Arup & Partners 25% overstress permitted by BS449. dimensionally identical main and secondary detailing of the main members and their (Photo: Mike Shears) Foundations are designed to have a factor of the mid '60s it has been quite unusual to find beams which nicely unifies the design and connections. The maximum force in the 17' safety in excess of the tower structure. The steel frames. Their use is usually confined to facilities service runs. / factor of safety appropriate to uplift, down- chord of the main portal is of the order of penthouse level. thrust, sliding and overturning is a minimum 25,000 kN. The major members are H or Sports halls Factory walling value of 2.0. It is also advisable to check that channel sections built up from up to 38mm These invariably use steel roofs and often We have been involved in the development of an adequate factor of safety exists for an plate. The result is a clean appearance on steel columns, as the scale tends to be more a steel factory walling system to meet a extreme or survival wind condition. both external faces of the steel members, modest than elsewhere and comparatively particular brief. This uses 1.2mm thick with a minimum interruption by gussets. little scope for the spectacular has been galvanized metal in interlocking trough form, Deflection Hangar doors available. 500mm wide x 100mm deep, spanning 7m This may be considered as a serviceability Each hangar has four door sections moun• limit state for the design of microwave ted on a twin track system to close them. towers. The acceptable limits of deflection The track system is continuous from one end vary from aerial to aerial which in turn are of the complex to the other so that in the related to the frequency band of the event of one complete hangar frontage microwave system. Tall, slender structures needing to be opened, all four door sections ! will tend to deflect more than fatter ones for are moved to the frontage of the other » the same applied loading. However, the mm hangar section. Each door section member sizes for slender towers may be comprises two leaves with a fixed link larger than the equivalent members for wider between them. Each leaf has its own drive v towers to carry the applied loading. On the mechanism. other hand wide towers tend to require more / bracing and will therefore attract more wind (5) IRELAND loading. The objective therefore is to juggle Ove Arup & Partners in Ireland, founded in Fig. 5 the geometry so that the strength and 1946 in Dublin now operates also in Cork, Bailey's Irish deflection requirements are achieved for the Waterford and Limerick. Total staff numbers Cream factory: T minimum weight of steel. are about 140. Most of the work is located in lifting the Ireland with a small amount in the UK, space frames. Selection of member types Middle East and the Third World. While the Architects: There are three main types of steel sections bulk of the projects are buildings in some Scott Tallon used in tower design; tubes, equal angles form, an increase in civil works content has Walker Ai and cruciform angles. The advantages and recently developed in the practice. vertically between roof and floor. Horizontal ribbed metal cladding to stabilize the open the base width and method of installation. Also, the angle 8, between the bracing and sides of the trough enabled us to provide a Towers and They are fabricated and transported in the leg member, should be maintained within 150mm overall thick frameless walling relatively large sections to minimize erection the following ranges: system. This system was designed, tested flare stacks time. Aggressive environmental conditions o and successfully used in a pilot scheme and infrequent 'safe' access periods are bolted structures 20°<6<90 where no commercially available system taken into account by specifying high quality welded structures 30°<9<90o could be found. John Tyrrell materials and workmanship. Solidity ratios: Central Bank of Ireland head offices Transmission towers are required to support Typically solidity ratios for different widths This design was conceived as a major land• Introduction the overhead power supply lines at relatively are as follows: mark in Dublin city centre and is unique in its Towers are by implication tall structures that frequent centres. The power lines are reach above the surrounding environment. tensioned to reduce the catenary effects and structural design in Ireland. Measuring 45 x Panel width Solidity ratio 30m, its seven floors are suspended from the They are commonly used to support suspended from an arm arrangement as part < 1.5m 0.25 roof and supported by two concrete service equipment or some installation at a required of the tower. This in turn creates forces in the < 5.0m 0.20 towers. elevation as part of an engineered system or tower in addition to the wind load. Also tensions in the power lines are affected by <10.0m 0.15 All floors are formed of structural steel process. climatic temperature variations. Because of <10.0m 0.10 trusses with a thin concrete slab. Each one The greater part of our work in this field has the number of towers required for any one is suspended by 12 pairs of Macalloy bars on been associated with towers supporting Factors affecting the design system the cost penalty for conservative the perimeter, directly to roof level. A system microwave antennas but more recently we design could be significant. The design Project requirements normally provided by of roof trusses enclosing the plantroom is have designed a number of structures for approach therefore is to test a tower or the client or the systems engineer include: the primary steel structure carrying all the supporting gas flaring systems and vent number of towers to failure, so the strength site location and particular details that are floor loads into the concrete cores. Floors pipes. Similar structures that we have of all members, including those normally known to provide a constraint of one sort or were fully assembled at ground level and designed or analyzed include lighting assumed to be redundant for analysis another on the design jacked into position, using the British Lift towers, towers supporting water storage purposes can be properly evaluated. Slab heavy lifting system located on the tanks as well as guyed structures. However, basic wind speed, the combination of wind and ice accretion and temperature where roof. this paper concentrates on microwave General tower arrangement appropriate Papal cross and canopies: towers and flare towers. In cases where the tower geometry is not size, type and number of items to be Phoenix Park, Dublin Fig. 6 Central Bank of Ireland head office under construction. Architects: Stephe Clearly there are similarities between the given or determined by factors other than supported at specified levels including An inception to completion period of two Gibney & Associates different types of structure but the strength or deflection the following operational or performance requirements of associated feeder systems months was achieved for the erection of a empirical rules for microwave towers may be the system determine the functional limits on the twist and tilt for the structure 35m high steel memorial cross for the 1979 applied as a first stage towards achieving an requirements of the structure in each case. design life of the structure Papal visit to Dublin. A fabrication using six economical design. Steel is favoured largely because it can aircraft warning lighting universal beam sections, each 600m deep, to Slenderness: easily be fabricated as component parts and painting and protection. form both stem and arms was devised, The ratio of the overall tower base width then transported and erected relatively On occasions we may be required to carry designed, fabricated, painted and erected should not exceed the values tabulated quickly and simply in remote locations. out wind speed investigations where with very little time to spare. below. Types of structures sufficient details are not given. Also, it is quite frequent that further interpretation of There are two main generic structural forms: Tower Maximum Fig. 7 self-supporting towers and guyed arrange• height deflection the design requirements is necessary. Papal Cross being hoisted into ments. Self-supporting towers are normally 0.75° 1.2° 1.2° In addition to the specified requirements position - Phoenix Park, Dublin of the open lattice type and may be either there are other factors that are likely to 50m 6 8 10 square or triangular in plan. Guyed influence the design such as economic and structures may comprise a vertical or 50-100m 5 7 9 practical considerations. For example the inclined slender stem with the stiffness 100-150m 4 6 8 availability of steel sections locally, provided by the guys. The combinations and transportation, lifting and erection, the Fig. 8 applications of these types of structure are Top width: maintenance of the structure and the Papal Cross and canopies as seen too numerous to cover adequately in this 2.25m for square towers with internal equipment including access are all parts of during the Papal visit to Dublin paper and therefore it is intended to consider climbing ladder; 1.65m for triangular towers the equation. Also, the lightest possible microwave and flare towers only. A brief with internal climbing ladder; 0.45m for structure is not always the most economic, « description of the main characteristics of towers with external climbing ladder. particularly where some standardization can each system is given below. Reference is Leg slope: be achieved and where there are difficult also made to transmission towers where a The slope of the tower legs at the base ground conditions and the cost of the different design approach is adopted and should be such that the point of intersection foundations may be a significant part of the different loading conditions apply. of the projected lines of the legs occurs overall cost. Microwave towers are usually constructed above the two thirds point. Loading from tubular and/or angle members bolted Wind together. For a particular network they are Panel types: commonly arranged as a family or families The optimum height to width ratios of the A basic wind speed corresponding to the 3 of towers. Each family typically consists of a typical panel bracing arrangements are: second gust with a return period of 50 years number of panels arranged vertically. Panels is usually adopted for the design, or service• can then be omitted either from the top or Height/width Panel type ability condition of the structure. On from the bottom for the required height. h/w>1.5 Z occasions an extreme or survival wind speed Each panel is braced in elevation and 1.00.85 F'c bD the various Steel Information Centres in Priorities for future activities and research From the investigations described in the (4) BOND, G.V.L. Fire and steel construction. Western Europe. Replies were received from (Refer to Fig. 3) Centres in nine countries. preceding chapters we concluded that the Water-cooled hollow columns. Con- wider and better use of steel in building will strado, 1975. Fire exposure and fire resistance calculation He = FyAs mainly be achieved by a reform of Fig. 2 All countries favoured the acceptance in (5) COWARD, S.K.D. A simulation method for Hcc = 0.85 F'c bD regulations based on: national regulations of a calculated design estimating the distribution of fire Hsc = FyAc where Ac: Area of steel fire, taking into account fire load, ventilation • a more precise definition of performance severities in office rooms. Building compression and compartment size, as an alternative to requirement Research Establishment Current Paper 0.85 F 0 85 F the standard fire resistance test. It is • a more precise estimation of structural CP 31/75, April 1975. r For equilibrium: accepted generally only in Sweden. performance and for designers: (6) AMERICAN IRON AND STEEL He =Hcc + 2Hsc f t ' ' FyAs = 0.85 F'c bD + 2FyAc In only three of the countries (France, • design manuals for the structural INSTITUTE. Fire-safe structural steel. A Sweden and Switzerland) is calculation of design guide. Washington, D.C., 1979. engineer Hcc As-a85FCbD the fire protection needed generally Hence Ac = 0.5 • simple design guides for the architect (7) LAW, M. and O'BRIEN, T. 'Fire safety of "i-fcf 2 H Fy accepted as an alternative to standard fire and engineer which show how much bare external structural steel'. Constrado, resistance tests. The other countries were in protection, if any, is needed for the 1981 dn can then be found from properties of steel favour of calculation, but one (Germany) only structural steelwork. (8) LAW, M. Fire safety of external building CG of steel beam sections. The code then gives a formula for sometimes. Performance requirement elements - the design approach. Eng• H? determining the ultimate moment of CG. of tension Only two countries (Sweden and A performance requirement should state the ineering Journal. American Institute of resistance when the axis N-N is located in Switzerland) have agreed representative objectives of providing fire safety - whether Steel Construction, Second Quarter, pp the flange or in the web of the beam. values of fire loads for a range of buildings; it is for the protection of people (occupants, 59-74, 1978. AS 2327 contains clauses which modify the the Netherlands for office and residential neighbours, fire fighters), the protection of (9) CONSTRADO. The behaviour of steel 2F, assumed stress block when the depth of buildings only. property (contents, structure, neighbouring portal frames in boundary conditions. Fig. 3 stress block would theoretically be located 8 A 'critical' steel temperature can be defined buildings) or a mixture of both. Ideally, the Constrado, 1980. below the top of the rib of the decking. Working stress method Ductility Permissible stresses and deflections are Design of composite sections by the working To ensure a ductile response of the beam based on extensive load testing and are stress method is in accordance with elastic there is a requirement that the depth of the nominated in the manuals. theory using a transformed area approach neutral axis of a T beam shall be not less Fireproofing and assuming no slip at the concrete steel than 16% of the overall depth of the section. Based on full scale fire tests, design criteria interface. The area of slab in tension is Shear connection have been determined under which, for given neglected in calculating the area. The function of the shear connector is to slab thicknesses, the provision of fire Rules are given for calculating the effective transmit horizontal shear between the emergency reinforcement will enable fire moment of inertia and effective section concrete slab and the steel beam and to resistance ratings of up to three hours to be modulus where profiled sheeting is used. ensure that there is no physical separation. achieved. This means that only the Permissible stresses are the relevant values Regardless of the method used to determine supporting steel beam requires spraying or in the steel and concrete codes. the flexural strength, shear connectors are other measures to achieve a fire rating. The designed by the load factor method. provision of this reinforcement has been Serviceability Characteristic strengths of both stud and established for given spans and Stress channel connectors are given for various superimposed loads, and is usually a For unpropped construction the stresses in concrete strengths. Connectors are provided considerably more economical way of the steel beam must not exceed 0.9 Fy under to resist the whole of the compressive force achieving the necessary fire rating than serviceability loads. and are usually distributed uniformly spraying the metal deck soffit. Deflection between the points of zero and maximum Practical considerations Deflections can be calculated using a moments. Where beams support heavy Shear studs welded through the decking are modular ratio of n for transient loads and 3 n concentrated loads, distribution should be the usual method of shear connection with for sustained loadings. A general deflection according to the shear force diagram. the concrete slab. It is important to ensure limit of span/250 is suggested with span/ 500 Transfer of longitudinal shear in concrete that there is an adequate power source and or an absolute value of 20mm where damage It is necessary to check potential shear that the interface surface between the could result from deflections. failure planes to ensure that the horizontal decking and the steel beam is clean, dry and Deflections during the construction stages, force can be transmitted to the concrete. The free from loose rust or scale. particularly for unpropped construction, code requires minimum transverse reinforce• Consideration should be given to applying should be borne in mind when considering ment to cross the shear planes in the bottom the studs in the field rather than the fabric• the need for cambers. of the slab. ation shop because of the risk of riggers Vibration Composite decking erecting the steel tripping on the studs. Comparatively light structures can result An Australian code covering composite Stud shear connectors adequately fix metal from composite design and the Australian slabs is yet to be prepared. At present only decking to support beams. Alternatively code gives guidelines aimed at limiting two types of decking are available for use in puddle welds can be used. damage to the structure or discomfort to the composite deck construction. Propping of the decking may be necessary to occupants. Both deckings are galvanized and available limit deflections during concreting. Altern• (a) Floor frequency should be greater than 5 in two thicknesses. Design manuals enable atively, propping can be avoided by locating Hz for occupancies such as residential selection of slab thickness and negative the support beams at appropriately close floors and schools. mesh reinforcement for simple loading spacings. Figs. 3-4 (b) Floor frequency should be greater than 10 situations. Full design procedures require: If there is no propping, deflections can be of Bush Lane House, London. Hz for repetitive activities such as sufficient magnitude for the concrete (a) Check on panel stress during Designers: Arup Associates. dancing, unless there is a large amount actually placed to be significantly more than construction loading (Photos: Arup Associates) of damping. (b) Check on panel deflection under the quantity calculated from the theoretical (c) Transient vibrations can cause discom• construction loadings thickness. fort or annoyance to occupants, and (c) Shear under construction loading Soffit fixings for example, the protection needed for other are nominally the same will vary from fire resistance in excess of 30 minutes either specialist literature should be consulted. For soffit fixings to hang ceilings, ducts, (d) Total panel stress due to slab dead load steel sections, for other periods of standard laboratory to laboratory: This is not the steel sheet must be insulated by a (d) For further guidelines reference can be pipes, etc., the metal decking must be and superimposed loads fire exposure or for non-standard fire surprising since, apart from any differences coating or suspended ceiling or the concrete made to a paper by D. L. Allen: drilled. Flash welding pins are not regarded (e) Shear and bond on the composite slab exposures (compartment fires). in heating characteristics, the real degree of must have reinforcement. Although 'Vibrational behaviour of long span floor as satisfactory. In the case of Bondek The most commonly used method of restraint of the specimen is quite often numerous fire resistance tests have been slabs'. Canadian Structural Engineering (f) Deflection of the composite slab special nuts can be fitted into the flutes to exploiting the results of fire resistance tests unknown and may vary during the test. This carried out, it is difficult to generalize the Conference Proceedings, Toronto 1974. (g) Concrete stress in the composite slab. support lightweight ceilings. is to assume that failure is related to the is particularly a problem with slender information received so that a design attainment of a critical steel temperature columns. method can be provided. Most tests have and to devise scaling methods or charts It can well be argued that the standard fire been for statically determinate floors: better based on a simple model of heat transfer resistance test is only a blunt instrument performance has been measured with from the furnace, through the cladding, to and in practice it serves its purpose because continuous floors. Although in some Precedent in design arises from a number of upset when some of the parameters change the steel. This method avoids any definition there have not been any serious structural countries the failure criterion for a floor is a Precedent sources - legislation, materials, manu• either in the problem or its solution. The of the structural behaviour or thermal failures in fires. If this is true it can also be deflection of span/30, these slabs can reach facturing constraints, form and appearance precedents remain - an early steam engine characteristics of the cladding; it provides argued that calculation methods are just as a deflection of span/20 or more while still and intuition - and our own ability to analyze problems. is given a fluted chimney representative of extrapolation of the result for the particular likely to give the 'correct' answer and are retaining load-bearing capacity. A failure The danger in following a precedent is when Greek Order. Only later and possibly in mode of failure experienced in the test. It much cheaper. It then follows that the fire criterion of infinite rate of deformation is in design the context changes so that the solution is partial recognition of this estranged can be used to predict results for standard resistance test should be re-designed so as therefore more appropriate. Heat transfer situation is an intuitive solution developed fires, but not for compartment fires. One way no longer appropriate. to provide information for these calculation calculations have not so far been very - result outcry. But the general solution for of extending the use of standard test data to John Roberts Extrapolation requires care. Precedent methods. successful probably because the method relieves Society's concern about radicalism chimneys continues to be adopted and it compartment fires is to establish an needs to be more complex for concrete than but can lead to anonymity and irrelevance. becomes a norm. And so the life cycle of the equivalence between the standard fire and Suspended ceilings for steel. design process repeats itself. compartment fires in terms of their heating Fire resistance tests have demonstrated the Overture Derek quoted Blake's 'Auguries of Inno• Composite steel and concrete beams effect on the structural element, the effect value of suspended ceilings for the No seminar is complete without an historical cence', 'we are led to believe in a lie when we To illustrate the impact of precedent and Tests have been carried out with both being attainment of a certain critical protection of steel beams and floor systems. review of the subject in question. It allows us see with, not through the eye'. intuitive thinking on the design process, isostatic and hyperstatic beams for varying temperature. A calculation method has been proposed to compare past achievements with present Intuition on the other hand is our ability to Derek chose a number of key events in conditions. Some large temperature which could be used to generalize test data, efforts. Derek Sugden's talk was as timely as find new solutions to novel problems. It history when either the problem set the gradients were measured in the steel, but the main problem is probably the it was fascinating. He led his audience, requires that we cast aside predilections and designer changed - in context or scope - Deficiencies of the standard test between the flanges and over the supports. difficulty of ensuring that the ceilings are through the mysteries of design achieve• solve the problem on its own merits. Voltaire or when new solutions presented themselves An examination of standard test procedures A calculation of critical temperature installed correctly in practice. The detailing ment from early China to just short of the in the 'Temple de Gout' summed up his - either from developing technology or the and the results obtained exposes several assuming a uniform temperature across the of the suspension system, lighting fittings, present day. The achievements of present appreciation of intuitive design in this way: skill of an individual. deficiencies. First, it has been observed that section is in reasonable agreement with the etc., is of great importance. day 'luminaires' - his term for the ack• 'Simple was it noble architecture. Each Scherzo: Historical examples of the some cladding materials in accidental fires average of the temperatures measured on nowledged leaders of contemporary design ornament arrested, as it were, in its position influence of precedent and intuition may undergo physical changes not Composite steel and concrete the upper and lower flanges. However, the - were left for another day - a pity. seemed to have been placed there of The conflict in China: displayed in the standard test, because of Structural analysis of composite steel and calculation of the heat flow to the section higher fire temperatures in the compartment. could be complex and has not yet been Of course Derek cheated. The talk was not, necessity.' There are early examples of the precedent/ concrete is difficult to carry out for normal For this reason a high temperature test, attempted. as billed, about the skeletal frame. Instead Throughout history intuitive solutions to initiative dilemma. In 8th century China, the conditions. It is not surprising, therefore, if it supplementary to the standard test, is he talked about the design process. Few design problems have, at least initially, design of timber buildings was highly presents problems of analysis under fire Single elements and frameworks sometimes suggested. conditions. Nevertheless, it ought to be realized, fewer cared for the audience was received a hostile reception, mostly, one regulated by the State through detailed Fire resistance tests are normally carried out Secondly, unless the test is part of a possible to carry out fire tests which would caught on the horns of the theme dilemma. suspects, because they represent a break building codes. These reflected the for single elements. The relationship research programme, the initial properties of lead to a definition of the critical conditions To what extent is (or ought) design to be with tradition. By repeated experience, technology commonly used and dictated the between the behaviour of these elements for failure and lay the basis of a design constrained by our own expectations - however, an intuitive solution becomes appearance of the end product. But this the specimen are not measured. The test when supported in the test furnace and method. 'precedent'; and to what extent is it (or accepted and the general public begins to same society had built a large span masonry load is related to the characteristic strength, when installed in a building is not well should it be) a function of our own associate the intuitive solution with that arch bridge (c.610) and a post and lintel not the strength of the sample tested. Profiled steel sheet and concrete floors established. Work on loaded external 26 immediate emotion - 'intuition'? particular problem. This happy balance is bridge (c.820). Thirdly, the results for test specimens which Test data so far obtained indicate that for column and beam assemblies shows greater In certain circumstances there are no fire diameters which are an order larger. maintained even though local flange The arch bridge bears a close resemblance Early examples resistance requirements and the steel needs However, the effect is only likely to occur for temperatures up to 800°C were measured. to Lutyens' Runnymede bridge of 1935 of precedent and intuition no protection. When protection is needed large heat-inputs, when columns are heated Results such as these, if generalized, could (though the connection is not thought the following measures may be possible: over two or more storey heights. greatly extend the design method. In the deliberate) and also with Arups' own bridge Design methods are available for replen• original analysis of external fire exposure8 • exploiting the advantages of low stress, Fig. 1 at Runnymede (which deliberately con• ished water-cooled systems which deal conservative assumptions were made about large massivity Temple gateway near Canton strained itself within the earlier precedents mainly with the assessment of the amount of wind effects because of the lack of test data. • placing elements outside the building centuries of precedent though not without modification). water storage needed to replace the water More information about the effects of Substitution of new materials: • cooling elements by automatic water embodied in an 8th century boiled off, and the associated supply through draughts would be valuable. Unaware of the Chinese precedent, intuitive spray building code systems* These methods are related to No requirements for fire resistance designs for bridges appeared in Europe • cooling hollow elements by water filling exposure from the standard fire and take no There are certain circumstances where it is Fig. 2 much later - Leonardo's temporary bridge • placing screens (false ceilings, partitions) account of how the fire might behave in generally agreed that fire resistance is not An-Chi Bridge of 1490 and Rennie's Wye Bridge at between the element and the fire practice. needed on the grounds of life safety: for across Chiao Shui River - Chepstow are good examples. example, single-storey buildings and roof engineer's intuition When it was decided to bridge the Severn at • cladding the element with an insulating Concrete filling material. Such materials can be structures are not usually required by of the same period Coalbrookdale, the natural choice of Because of expansion of the steel, there is intumescent paint, plaster, mineral fibre, regulations to have fire resistance if the material was masonry. But Coalbrookdale negligible cooling effect when hollow cement, concrete. They can be applied escape routes are adequate and there is was the centre of iron making in England in sections are filled with concrete; thus the alone or mixed, and sprayed, trowelled or little risk of fire spread to adjacent buildings. the 18th century and the architect Thomas main structural performance in fire in the form of boards. In other circumstances, however, fire re• Pritchard sought the choice of one 'iron- conditions is provided by the concrete core. sistance requirements are made without any mad' Wilkinson. Not surprisingly the bridge Steel without cladding A very large research programme has been clear indication whether these are for the was built of cast iron, which at least completed but it has not been possible to Fire resistance of protection of the occupants of the building, illustrates how architects can be affected by establish an analytical design procedure. unprotected steel elements or to assist the Fire Brigade to control the passion. The bridge is a good example of Some empirical relationships are available. fire. There is a tendency to assume that Where the performance requirement is how a new material - in this case cast iron Profiled steel sheet floors providing fire resistance for every element of dictated by building regulations then it is - is merely substituted in a solution for Profiled steel sheet may be used either as a structure must automatically increase safety clear that one must aim to provide a fire which a precedent already exists. The link in non-composite shutter or as fully composite for the occupants, when in fact other resistance of at least 30 minutes. For a given this case is the pattern maker whose skill in flooring for reinforced concrete slabs. When measures, such as smoke control or grade of steel and stress level, the fire forming the casting moulds parallels his resistance varies inversely with the 'section used as a composite floor it is difficult to automatic sprinklers, could be more ability to manufacture timber centring. factor' P/A m - 1, where A is the cross-section gain acceptance for more than Vz hour of fire effective. However, it is difficult to analyze area and P the exposed perimeter. Most steel resistance unless cladding is applied to the the problems and find the best solutions elements in common use have a section exposed face of the steel sheet or extra when the purpose of the regulations is not Bridge design 1 made explicit. There is no agreed basis factor of 250m - or greater and for an reinforcement is placed in the concrete. Fig. 3 unprotected mild steel element with the There is as yet no wide agreement on the available which defines acceptable levels of Runnymede Bridge by Lutyens 1935- usual design stress this gives a fire way to design such floors for fire resistance. fire safety for structures, taking into account Precedents resistance of about 15 minutes when the See also the section on profiled steel sheet the seriousness of the consequences of (Photo: Ove Arup & Partners) element is subjected to the standard fire and concrete floors. structural failure for either life or property. • resistance test. ('Massivity' is the inverse of Low fire exposure - internal It is by no means clearly established what the section factor). If the fire exposure inside a building is the performance of each element of sufficiently low then it can be established structure should be during the course of a To achieve larger periods of fire resistance it that the steel elements do not reach critical fire. For example, is it necessary for each is necessary to vary, either singly or in Fig. 4 temperatures and the standard fire exposure element of wind bracing to be protected? Is combination, the section factor, the stress Runnymede Bridge by Arups 1979 is not relevant. The best known example is the loading during the course of the fire level and the grade of steel. A column with changing significantly - either for the better Precedents with a certain style 1 car parks where tests have demonstrated P/A = 29m- (equivalent to a solid 140mm or for the worse? It has been suggested that (Photo: Ove Arup & Partners) that a fire involving a motor car is small and square) would give 30 minutes fire resistance if the wall and roof panels of an industrial 1 is not likely to spread to adjacent cars. In P/A = 11m- (equivalent to a solid 360mm building are destroyed quickly by fire, then addition, statistics indicate that the risk of square!) would give 60 minutes (average the steel frame is very under-stressed and fire occurring in a parked car is so low that it temperature of 540°C)3 can survive without cladding. This would has not yet been quantified. The relationship between fire resistance and certainly explain why unprotected portal Fire exposure may be low because there is a stress level can be estimated fairly readily frames in practice behave better than could small fire load in relation to the for elements with uniform temperature be expected when exposed to accidental 2 compartment size and ventilation. Methods distribution . However, it has been observed fires. A design method for unprotected portal in fire resistance tests that the temperature of calculating the potential fire exposure frames is available9. of steel beams varies both along and across already exist and a method of estimating the Steel with cladding the section and failure may not occur even distribution of severities of fire exposure in rooms (total burn-outs), using results of fire when the temperature of the lower flange In the selection of a material for fire load surveys, has been developed5. These exceeds 600°C. At the moment, since cladding, the designer takes into account analyses could be combined with statistical calculation methods assume a uniform the following factors: temperature distribution, correction factors data on accidental fire behaviour to provide have been introduced2. an estimate of the risk of a burn-out • suitablility for use and method of occurring. The beneficial effects of installation (architectural, environmental, Water cooling automatic sprinkler systems could also be technical and economic aspects) Water filling of hollow sections has become included. The types of low fire load buildings • thickness of the cladding according to the a well-accepted method of keeping steel for which such an approach could be cool without the use of cladding. The main fire resistance required (whether by test or profitable are low-rise schools, offices, by calculation method) problems are the avoidance of dry patches hospitals, sports halls and concourses in of steel which would overheat, and the bus stations, train stations and airports. • maintenance of its integrity and insulating provision of adequate water to replenish that Low fire exposure - external properties. which boiled away. A simply-filled column It is well established that at certain positions without replenishment can provide over 30 Results of standard fire resistance tests outside the facade of a building the fire minutes fire resistance, but not as much as In principle the designer considers two exposure will be so low that cladding of steel 60 minutes. Existing systems therefore aspects: elements is not needed. The external fire usually incorporate storage tanks and also exposure varies not only with position but • the heat transmission through the may provide extra water by inter-connection also with fire load, window area and shape, cladding material and the consequent of columns. Much interest has been shown temperature rise of the steel in the possibility of using simply filled non- compartment area and shape. replenished columns for two-or perhaps Design manuals are available to calculate • the structural behaviour of the heated three-storey buildings, the water in the top the external fire exposure and the steel element and the temperature or 6 7 storey being used to replace that boiled off consequent steel temperature . The design temperature distribution at which a should a fire occur in the lower storey. method has been used to calculate an critical condition occurs However, the likely flow pattern within the average temperature across the section, by and for these the necessary data must be heated column is not well established; it has analogy with interior steel elements. provided by tests. In practice, the only been suggested, for example, that the two- Although it was known that in practice there information likely to be available is the result phase flow of steam bubbles and water could be large temperature gradients there of a standard fire resistance test which gives Fig. 5 Fig. 6 could give rise to surging and large water were no test data available at that time the failure time for a specific steel element Longdon-on-Tern aqueduct Pont-Cysyllte aqueduct by Telford 1795-1803- losses. Existing data for two-phase flow which assessed the importance of this protected by a certain thickness of a specific by Telford 1795- Hailed by Sir Walter Scott as the greatest work have been obtained from tests with small effect. Later research with external material. It is difficult to separate out the an intuitive trial of cast iron of art he had ever seen diameter pipes (of order 25mm) and cannot column/beam assemblies under load information needed if the results of the test for a greater project (Photo: Architectural Association) be extrapolated with confidence to showed that mechanical stability could be are to be applied more generally to assess. Intuition and the first iron frames: The skeletal frame The first iron frame buildings in England had expansion and reduction of Young's Steel structures and fire safety no real architectural precedents except in Fire protection modulus caused by increase of temperature There is no evidence to suggest that in the external walls and the entasis of the cast and/or temperature gradients in the section. buildings designed to modern standards of iron columns. Early examples are at Milford Margaret Law In fires larger deflections than normal can be construction, the structural material itself 1792-3, Shrewsbury 1796-7, Salford 1899-01, accepted, generally at least span/30. has an effect on the life risk, i.e. there is no Leeds 1802-3 and Belper 1803-4. Because of its high thermal conductivity, reason to believe that a person in a modern Introduction The use of iron spread to the external walls uniform temperatures are attained rapidly in steel-framed building is more likely to suffer as in Arkwright's Masson Mill, Cranford, In 1980, Ove Arup and Partners and CBLIA many steel sections. For a given rate of injury or death by fire than a person in a • (Centre Belge-Luxembourgeois d'lnforma- 1783, the cast iron Doric columns in heating, a heavy section will heat up more modern building of concrete, brick, wood or tion de I'Acier) completed a joint study of Hartley's Liverpool Dock, 1845, and the boat slowly than a light one; the massivity of the masonry construction. research into the behaviour of structural store at Sheerness, 1858-60. In each case, section (volume in relation to exposed Most major property losses in fires are those steel elements exposed to fire. The study however, elements of the iron construction surface area) has a significant effect on its in industrial buildings - warehouses and was financed by the European Coal and were constrained by precedents developed performance in fire. large production and storage areas - and it Steel Community (ECSC) with the purpose of rationally in other materials. is the loss or damage of the contents which identifying priorities for research in the field The metamorphosis of the column: makes up the main cost of the fire. The of fire safety of building construction. We The trabeated form of architecture (column Fig. 7 Fig. 8 causes of fire spread include such features interpreted the broad purpose of ECSC- as combustible materials on wall and roof and lintel) was derived for masonry Albert Dock buildings in Sheerness Boat Store Liverpool by Hartley 1848 by Col. Green 1858-60 funded research to be to increase the use of surfaces, delay in detection, lack of compart- construction by Greek intuition. The practice the Doric Columns are cast iron the frame emerges steel in building. We therefore tried to mentation and poor details at junctions of of shaping the columns to suit the identify not only obstacles to the use of steel compartments. There is no reason to believe perspective from which buildings were most but also circumstances favouring its use. that the use of steel construction is more frequently viewed and the decoration to the This note summarizes our findings and likely to lead to these major fire losses. column capitols and shafts became includes some later information. embodied in strict 'orders' which were Behaviour of steel in fire written down and illustrated. Thanks to As with other structural materials, the Fire protection of steel J3 Vitruvius, the rules were preserved so that by 3 mechanical properties (tensile strength, Properly designed steel construction can the time Europe had emerged into the yield strength and Young's modulus) give adequate fire resistance and in many Renaissance, there was an established decrease with temperature. Values have It situations subsequent repair, particularly for precedent for the appearance of columns. been codified for design? Mild steel, pro• mild steel, is a simple operation. In certain When masonry was replaced by a new 'MriFi,, vided it has not exceeded a temperature of circumstances very little fire resistance may material, cast iron, designers found it hard to • - 'MM. about 900°C, recovers most of its strength be needed, either because the potential fire break with convention. Hence Jesse op cooling. exposure can be demonstrated to be low or Hartley's cast iron columns at Liverpool because the steel can be sacrificed in the dock, already mentioned, although The heated steel element will fail when the event of fire without prejudice to the overall handsome, were stone look-alikes. And in yield stress decreases to the value of the fire safety objectives. the first iron-framed buildings, the cast-iron working stress. (This can alter with the Normally, it is necessary to design the columns remain constrained by precedent. formation of plastic hinges.) The steel elements so that the steel does not reach its temperature at this moment is defined as the The reason not to break convention is critical temperature within the fire resis• critical temperature. It depends essentially unclear. Possibly it was the fact that a tance period imposed by regulations. Regu• on the loading, the degree of restraint, the column is a plain affair as defined by lations take into account experience of end conditions, and the type of steel. It is function. The link that allowed the precedent building fires and, in a somewhat arbitrary therefore a mistake to define a single value, to be followed was the technology of timber way, the nature, height and use of the 540°C for example, for the critical - used as patterns by both masons and iron Fig. 9 Figs. 1-2 building. The periods of fire resistance speci• temperature of steel. founders. Guaranty Building, Buffalo, USA The Centre Pompidou, Paris. fied range from a half hour to two hours, or 1894-95, facade Before the element attains its critical tem• Architects: Piano & Rogers even four hours for certain locations deemed Not knowing how to deal with columnar perature, it can deform under the effects of (Photos: Ove Arup & Partners) to be particularly dangerous. elements seems to have persisted as a problem, for we find many otherwise Fig. 10 functional objects having classical embel• Shell Mex House 1933- Portland Stone lishments. Even Robert Stephenson quarries hung on steel frames as succumbed. In 1830, one of the locomotives architecture is sacrificed on the he designed, The Northumbrian, was put into altar of structural engineering service resplendent with a Corinthian fluted (Photo: Architectural Association) chimney. The designer's dilemma in defining an Meads Station, despite their theoretical strength particularly in tension. Adler and intuitive solution in cast iron was only rarely relevance to the hammer beam roof of the Sullivan are usually credited with designing solved elegantly. By 1874-75, Jabrouste was shed, give the edifice the air of a 'mere the buildings which are regarded as the first able to define an altruistic form for the cast caricature'; 'mock castellated work, shields modern steel frames - the Casson Building iron column in the second of his library without bearings, ugly mouldings, no- and the Pirie and Scott Building, both in buildings - the National Library. Gone is the meaning projections and all sorts of Chicago, and The Guaranty Building, Buffalo. ornamentation and the iron foliage. Instead unaccountable breaks .. . make up a design Engineers' architecture and more conflict the columns merge with the domes they at once costly and offensive and full of with precedent: support and the form expresses the pro• pretensions'. Clearly heresy must be Meanwhile engineers were finding other cesses of rolling and forging involved in their stamped out. Thus did the Christian novel applications for which no architectural manufacture. Only the shaft remains fluted Functionalist give his verdict on what was precedent existed. as a throw-back to earlier precedent. certainly 'engineers' architecture'. 1 As we shall see later the problem of the Between 1795 and 1803 Telford constructed The skyscraper is born column was more generally overcome the Pont Cysyllte aqueduct carrying the Notwithstanding such attempted divine because of two factors - firstly the need for Ellesmere canal over the River Dee near 1 interventions the use of metal frames pro• fire protection; secondly and more important Llangollen. The form of the iron trough gressed, if only slowly. By the middle of the the fact that concrete and steel had become spanning the masonry columns is simplicity 18th century, iron had been used in widely available by the 1890s and these did itself, echoing only the loads being resisted, commercial buildings on both sides of the not permit the easy copying of Greek order. and has no formal memories. Sir Walter Atlantic: Jamaica St., Glasgow and Oriel Scott called it: 'The greatest work of art he Chambers in Liverpool (whence the oriel Railways and the ecclesiologists hit back had ever seen' - praise indeed. Incidently window) and buildings by Bogardus and the The rapid development of the railway from the work of art was only produced after Badger in New York (including the Otis 1825 onwards gave engineers rather than Telford had successfully tried out the design Building containing the first public lift.) architects the chance to produce iron on much more modest scale at Longdon-on- Bogardus' buildings caught on fast as they structures for an entirely novel set of require• Tern in 1795. were available ex-stock in kit form and it took ments and this they did. Lime Street, Then came the Forth Bridge designed by the concerted efforts of the New York Liverpool 1836, Euston, the Trijunct at Derby, Messrs. Fowler and Baker, built between Architects to have fire codes changed Temple Meads and York are all early 1883 and 1889 and representing a scale effectively to put an end to his challenge to examples. This new-found opportunity to change in the possibilities of steelwork their province. derive new and appropriate solutions in new construction. It too attracted influential materials and for new uses did not go About this time the initiative in building critics. William Morris said 'There never unchallenged. How dare classical style be frame design crossed the Atlantic, would be an architecture of iron, every ignored. Pugin in his 'Apology for the Revival germinated, then took a leap forward with improvement in machinery being higher and of Pointed or Christian Architecture' felt that the manufacture of steel sections which, higher until they reach the supremest 28 the Tudor embellishments to Brunei's Temple unlike their iron antecedents, were of higher specimen of all ugliness - the Forth Bridge'. Lunokhod 1, which landed on the moon in need to be careful, as recent developments fabricators do not like quoting main contrac• entirely a steel solution, with lightweight The life cycle of the intuitive process: illustrated by the work of Labrouste in automated fabrication processes are in tors for steel sub-contracts, as they cannot steel or aluminium cladding. At one stage, 1970 looks like a traditional samovar. The part changing the scene, and are making be sure they are quoting to all the main for planning and other reasons, the rise of the corporate client has also brought seemingly more complex fabricated shapes contract tenderers, and are certain to incur claddings to a two-storey office block were with it new problems for the designer. The more economical through reduction in far greater tendering costs, which will of changed to brick, and the frame changed to principal of these is his inability to deal with weight. course have to be passed on to the clients. concrete, because the architect preferred the totality of the design problem. He now Complicated measurement is often em• detailing brick supported by concrete rather Again measurement methods and contract finds himself pari passu with the executive in ployed, even for very small works, and than by steel. This illustrates that con• procedures must be considered as part of a niche in his client's hierarchy. The very inequitable conditions of contract imposed siderable effort is needed to change that the design criteria. Constrado have recently essence of design is the need to transcend on the small man. Recent examples of this confidence factor, and also the obvious point (perhaps belatedly) published the result of artificially created boundaries. The threat of on a small steelwork sub-contract have pro• that, taken together, a decision for steel independent assessments on several case the corporate client is the precedence of his duced tender figures perhaps three times as cladding and steel frames seems 'right' studies which show steel-framed buildings own organization. Unless great care is taken, high as might be normal. By and large, this whereas the heavy cladding seems 'wrong'. to give very considerable savings in time an intuitive design approach can cause kind of difficulty does not apply to reinforced Why? over any reinforced concrete alternatives, ructions. We have not yet learned how best concrete work, and so we have to be careful • but much would depend on the contract The question of fire protection is fun• to relate to the large corporate organization to ensure that the right procedure be used if • procedures adopted, for it can very easily be damental. The addition of mineral fibre and yet still retain our ability to innovate. the overall aim is to be achieved. Fig. 11 shown that in many cases to achieve the sprays or dry claddings, etc., increases the Coda 1 and 2 Two new graduates from different univer• St. Genevieve Library 1843- banded savings in time, steelwork sub-contracts cost of the frame by more than 30% in the Derek summed up his talk in two thoughts: sities in the UK were interviewed recently to barrel vaults in stone replaced by have to be let before the main contract, UK, although this perhaps represents only (1) Most architects' work and most of our see if their courses were perhaps biased banded barrel vaults in cast iron committing the client to a process which he around 12% of the total cost of the (Photo: Architectural Association) work is concerned with buildings which lie in towards concrete, rather than steel, and it might not want. New forms of contract such structure, including floors. In the USA the scale between the house and the tower or was quite encouraging to discover that there as the JCT 80 in the UK are making increase is less because, presumably, there was no bias. Both left university equally in• bridge where the structure is dominant. At nominated sub-contracts less attractive to is far more competition in the fireproofing Fig. 12 experienced in the two materials. However, it this in-between scale, whether structure is clients, and there are vested interests which market. Within the fireproofing element, by Bibliotheque Nationale 1862-8 is plain, certainly in the UK, that from that expressed or not is a function of the make it harder for the consulting engineer to far the largest element is for treating the the arches which combine to support architect's personal morality of form. What stage forward familiarity with steel does not the domes give ornamentation from the overcome resistance to organizing contracts beams (70-75%) as opposed to the •am we find to day is a search for originality come easily. We have recently completed the geometry. The fluted cast iron columns in some other form to overcome this. In my columns. If we can do something to reduce where many of our luminaires cast light only design of a large and complex phar• remain inhibited by the tradition view this is something we must watch very the beam element, we may achieve on themselves, leaving principles in the dark. maceutical research laboratory, and this was of stone. (Photo: Rab Bennetts) carefully, particularly as there are signs that worthwhile savings. Lacking originality, there is an obedience to, but not a listening to the precedent. Misplaced precedent Remember Blake: 'we are led to believe in a Conclusions lie when we see with, not through, the eye'. There is much evidence to suggest that steel approach. There is nothing magic about The engineer for his part with his now very as a material is now relatively cheaper than designing in steel, but rather it is a simple powerful analytical tools - the new altars of it has been for some time, and is far more question of education and training. The our profession - is probably sacrificing his readily available. There is a growing demand industry has lost a considerable amount of intuition at an alarming pace, encouraged by from discerning clients and specifiers to experienced people over the years, and we the academics with which he spends the take account of this, and we should seize the must examine how we are going to fit into, or most formative years of his life. opportunity to promote its use in those even adapt to future needs. The characteristics sought today are those cases where we can gain advantage for our In designing in steel, we must not lose sight of performance, heat, light, sound, durability, clients. It could be quite a potent weapon in of the whole. This is true of any material, but Fig. 3 adaptability and so on. As we seek to specify our armoury. in the present state of the art, it is Hall 7, National Exhibition Centre them to define our places, we remove Birmingham: a successful use of There are, however, some obstacles in the particularly so for steel. We have seen how ourselves from the reality of the materials exposed structural steelwork way of the specifier and contractor in using contract matters, questions of measurement themselves. Architects: Edward D. Mills and Partners steel. Many of these should be quite easy to estimating, and speed of construction are all As we remove ourselves from the materials, (Photo: Ove Arup & Partners) reduce or even eliminate with the right major factors in the design process. we remove ourselves from the forms they take and thence from the development of Fig. 13 Fig. 14 any structural intuition. Northumbrian 1830 Emperor Hirohito of Japan (left) with (2) In the construction industry, new embellished with Stephenson's his chief of staff inspecting sound materials and their fabricated elements Corinthian fluting to the chimney detectors for locating enemy aircraft, Osaka 1934 replace or substitute for old materials. The form of the new copies the form of the old. Arch bridges in stone are replaced by arch Good stuff. Baker replied at the Edinburgh held, was of little value unless it was bridges in cast iron; cast iron baths by Literary Institute. He expressed doubts as to accompanied by practical experience, sound plastic baths in exactly the same form. whether Morris had the faintest knowledge judgement and bold initiative. In the St. Genevieve Library, 1843, Labrouste of the duties which the great structure had to Other protagonists of new technology were replaced banded barrel vaults in stone by perform. How then could he judge the tolerated more sympathetically. Perhaps the banded barrel vaults in cast iron. The details impression which it made upon those that forms were less outrageous even if of the arches clearly indicate they were could appreciate the direction of the lines of precedents were absent. Burton's cast' and the joints differentiate for us what stress and the fitness of the several greenhouse at Kew and Paxton's work at was made off-site from that connected on- members to resist the forces? Probably, Chatsworth and the results at the Crystal site. Baker went on, 'Mr. Morris would judge the Palace are testimony to this. Stephenson's At the time Labrouste designed the National beauty of a design from the same Britannia Bridge was much admired. (This Library in 1862-8, cheap puddled wrought standpoint, whether it was for a bridge a mile itself has been ruined by the intervention of iron was available. Here the arches which long or for a silver chimney ornament. It is an unsympathetic technological repair.) combine to support and define the domes impossible for anyone to pronounce A point had been reached where, for many have a completely different expression. The authoritatively without knowing its structures, the architecture was derived from parts are clearly rolled or hammered and functions. The marble columns of the the engineering. rivetted together. Process and engineering Parthenon are beautiful where they stand are evident with ornamentation from the but if we used it as a funnel for an Atlantic Without the development of architectural geometry of the parts and no cast foliage as liner, it would to my mind cease to be forms relevant to new technology, the in the first library. The column remains cast beautiful but of course Mr. Morris may think pendulum could swing even further from iron fluted and with an Ionic Capital - or otherwise'. precedent but also away from the intuition Baker recognized towards the god of one could say it remains inhibited, like all The dangers of new technology analytical methods. Shell Mex House, built 19th century columns, by the tradition of New technology could no longer be ignored in 1933, was described as architecture stone. by those supporting precedent, partly sacrificed on the altar of structural engineer• Reprise because technology had to be compre• ing, and the new wave of buildings as The theme dilemma - precedent v. intuition hended in order to attack it and partly Portland Stone quarries hung on steel - remains unresolved. But we are more self- because the technologists themselves were frames. aware. One wonders whether such self- not above abusing their new found talent. But even the epitome of advanced awareness is inhibiting. The next time you Benjamin Baker was very well aware of this. technology, the exploration of space, shows are detailing a concrete column to resemble His great dictum was that all theoretical us that the world of precendent remains alive the steel column the architect really wanted calculations involved assumptions that were and well, as comparison of Russian and if only the fire regulations permitted, will you often convenient rather than true; that they American man landing vehicles demon• be daunted? And will you be able to convince could be valuable as a check but disastrous strates. The Northrop Corporation 1966 lunar your peers of the wisdom of precedent and if accepted with blind faith. Technology, he vehicle is straight out of Disneyland. the need for intuition? 29 Industrial building: Fig. 1 - -10 Employment in the EEC steel industry Report from W. Germany Fig. 2 Birmingham Potential UK steel production capacity against actual UK steel production

150 Robert Greenwood potential production - Peter Handley * • France 100 Introduction Italy Birmingham Office has been involved in a actual production large number of single storey industrial buildings. These have ranged from small Britain extensions of 200m2 for family-owned Black Country businesses to a 20,000m2 ware• -12 house at Coventry. Belgium

Planning -5 Our experience has emphasized the need for Holland good planning and realistic prices. Indus• Luxembourg trialists in the West Midlands want two basic features for their buildings-a strong floor Dec 78 Sept 82 lib 70 75 and a good roof that won't leak. percentage change Good planning means designing a building Fig. 1 Coventry Trading for its immediate use whilst ensuring that it Estate from the air. will hold its value in the market place. Architects: W.S. Hattrell Steelmakers have had to make a real effort designs, and designers were lost to other units, and are difficult to access. Information Planning also means carefully balancing the & Partners to be more productive, particularly in the UK disciplines. Lack of understanding and on such vital issues as corrosion protection, minimum cost of construction with the where overmanning was serious, and market provision for maintenance probably also fire, special materials, welding and so on is future waste of money if the facility fails to forces have ensured that steel prices are caused the pendulum to swing away from not gathered into one centre of excellence, now cheaper than they have been for a long steel. In recent years, acceptance of and in some cases the information can even be adaptable or flexible. Fig. 2 Coventry Trading time, in comparison to the main competition weathering steels and the publication of far be better obtained elsewhere. Apparently, for An adaptable building will accept re- Estate: structure after of concrete. Figures show the change in the simpler codes and rules have swung the example, better advice on corrosion in steel planning of storage or re-organizing of fire which led to last few years to be quite dramatic, no doubt pendulum back, as have problems being can be obtained from the non-ferrous metals production. A flexible building will cope with provision of new even to an artificial extent because of encountered in the life of concrete finishes. trade association than from the steel expansion or alteration. building 2 government subsidies of one kind or another. The 20,000m warehouse we designed at In multi-storey buildings the pendulum had industry! In any event, familiarity in the use Certainly in the USA and the main EEC Coventry Trading Estate (Job No. 6670) five started to swing against steel much earlier. of steel at all levels of the industry has countries, steel is being sold at a loss, but declined, and this is no small obstacle to its years ago has already been used by Talbot Fig. 3 Warehouse As for bridges, regulations of one kind or even if this changes, it still seems likely that wide use. This lack of familiarity affects not as a 'knock down' production line for Alexander Duckham another were a contribution in the process, overcapacity will keep prices down to make only knowledge of the material, and analysis exporting cars to Iran. It is now used as their and Co. Ltd. Architects: but mainly covering other problems such as steel more competitive than in recent years, of complex details, but also the setting up of national distribution centre. It can, if needed Harper, Fairley fire protection. In some parts of the world, and supply problems are unlikely to be as measurement, cost control, and contract in the future be sub-divided into a number of Partnership fire regulations are not very onerous, or difficult for some time to come. procedures to take full advantage of smaller units. perhaps not enforced, with the result that So for the first time in many years, we find steel frames do not have to carry the potential savings of time and material in ourselves in a position where price and Adequate provision must always be made for additional cost and time penalty of steel structures in those situations where it supply issues are such that steel is a service loads and some spare capacity is encasement in concrete, spray coatings or could and perhaps should be viable. material which must be considered more always desirable - but there is rarely any dry linings. In some countries such as the UK seriously, particularly as many clients or Design approach need to provide for production loads. it would be held that fire regulations are too purchasers of construction are far more It has been mentioned • before that the Equipment and material handling can severe, or perhaps unreasonably interpreted, actively demanding steel, and are examining market conditions for steel are such that it is always be supported on a separate adding unnecessarily to the cost of steel alternative design and contract arrange• now relatively cheaper and more readily structure. This was done at Coventry and structures. We probably can all quote ments to achieve better results. If we do not available than for some time. With the also at Aldridge when a high level barrel- examples of that, and certainly many of us more actively make steel one of our design pressures to construct more quickly (always filling operation had to be included. must have felt from time to time that more skills, we will be doing both ourselves and there but probably now stronger as a result research is needed to understand better Layout our clients a disservice. of high land values and the high cost of what happens to steel buildings in fires - Structural costs increase with the span Obstacles to the use of steel borrowing), we must be prepared to take not just isolated members making up chosen. For light industry and small product The material conditions mentioned advantage of steel frames in the right frames. In Ove Arup & Partners, we are in a storage, 15 to 30m stanchion spacing is previously are clearly not the only reasons circumstances. better position than many to seek and obtain suitable. Medium production and general why use of structural steels declined in good advice on this, and probably also in a We have seen that the steel as a material has warehousing usually require spans of 24 to many of the world markets. Price and supply better position than most to encourage new become more competitive against concrete 36m. Heavy industries and high/dense difficulties played their part, but many other approaches, development of cheaper mat• as a material, but it is also worth considering warehousing often need spans up to 50m. factors also were of great significance. erials, and a wider understanding of the what is happening to the 'finished' product. Even in fields of activity where steel is a Selected examples main issues. natural,-things can go wrong which change On simple structural frames, such as Aspects of design and detailing can be high• the economic or technical balance. As an At the same time that these supply, cost, sections used in straightforward multi• lighted by examples of Birmingham example we have only to think about the box legislative and other factors have helped storey frames, the fabricated and erected designed projects. girder bridge. After the Second World War a swing the pendulum away from steel, the cost of the steel is perhaps more than Alexander Duckham and Co. Ltd. at Aldridge massive bridge building effort had to be influence of research and graduate design double the cost of the raw material. Possibly (Job No. 6619) required a new warehouse and undertaken in Germany to replace the aids promoted by the competing concrete now the labour costs are increasing faster 42mm diameter rod in Grade 50 steel with was necessary to repair some of the main filling shop of about 6,000m2 area with a hundreds of major structures destroyed or industry pushed it even further. In the UK the than the material itself, but in any event they High strength friction grip bolt connections. valley girders and the best solution was clear height of 10m and with a flat roof. We damaged, and the elegant and economical Cement and Concrete Association has most represent the area of greatest fluctuation. If The entrance canopy edge beam is a 30m provided by the site welding of new angle were appointed as prime agents with total box girder steel bridge emerged as a domi• effectively promoted the use of concrete, fabrication is complex or difficult, then the span box girder. members. To stabilize the gable ends, props design responsibility for all aspects except nant solution. Some 10 years or so ago the runs training courses for specifiers, clients, finished product cost can increase of rectangular hollow sections were used. the plant. The building has a structural grid The former Armstrong Whitworth Aircraft position was changed by the series of operatives and so on, and is a place to which dramatically, in some cases reaching more of 15m x 12m and we designed warren Factory at Coventry is now Coventry Trading The replacement building is 260m long x 75m failures in box girders, partly brought about many people in the building industry would than seven times the cost of the raw braced welded angle trusses at 6m centres Estate. This is a very long building with a wide with internal stanchions on a 20mx15m by a lack of understanding of both material turn for advice, They are a semi-independent material. with Multibeams as purlins. Universal width of 110m, having two spans of 30m and grid. Although we normally find that welded and geometrical instability in the thin plates. organization financed by a levy on cement In this age of increasing accountability, and column stanchions were used internally but one of 40m, and the roof is of steel angle steel trusses are the most economical for The reasons were of course complex, but sales which produces them an income of more measurement of everything, we are as a 4-hour fire rating was required at walls, riveted construction. As the result of a major this size of grid, we used plastically nevertheless one of the results was a new around £5-6m. per annum. In contrast, the often under pressure to produce maximum the perimeter columns were of precast fire near the centre of the building, we were designed portal frames and valley beams set of design rules (quite understandably) nearest equivalent in the steel industry in the area for minimum material, under the concrete. The supports for the barrel loading appointed for two structural contracts. and the bracings were circular hollow imposed on designers, which for a while UK is Constrado, which is wholly financed by proposition that this will equate to minimum area served by conveyors required 40 beams Rather than rebuild on the same area the sections. The portal frames will allow easy tipped the balance of economy away from the BSC, and in the minds of many is simply cost. Clearly this is not always so, and the of 15m span and here it was most client decided to have new gable ends to the construction of sub-division walls for any box girders to plate girders and even to not able to cope in the same way on a budget greater use of material, if accompanied by economical to use castellated universal parts which were saved from the fire (Job future re-organization. concrete. For a while, in the UK and else• of less than £400,000 per annum. The centres less fabrication and greater simplicity, can beams. The building was fully braced with 6591) and then provide a new separate At Icknield Port Road, Birmingham (Job where, there was a dearth of steel bridge of research and information in the steel easily be shown to produce a more angles at roof level but the side bracing was buildinn 'Job 6670). For the two gable ends it 6669), a number of 18m span steeply pitched sector are scattered around manufacturing economical result. However, even in this we Vol. 18 No. 2 July 1983 Contents For the 90m x 60m factory for Adamswear at Published by Nuneaton (Job 9195) our client instructed us Ove Arup Partnership 13 Filzroy Street. London W1P 6BO to prepare a performance specification so THEARUP that subcontractors could use either portal frames or trusses. The grid for the 60m width Editor: Peter Hoggett is two spans of 30m with a 6m spacing down Art Editor: Desmond Wyeth FSIAD the length of the building. The truss design Assistant Editor: David Brown JOURNAL proved the most economical. The structural steelwork industry: 2 Trusses were also used for a 20m span tank A review, production shop for Joseph Ash and Sons by R. Haryott (Job 9580) and also for an awkward re• Fire protection, 5 development of an existing site for Samuel by M. Law Heath and Sons (Job 8567) which required some operational areas to be kept in Towers and flare stacks, 9 production while the new building was by J. Tyrrell completed around them. The use of plated steelwork in 12 a tension leg platform design, Figs. 4-5 by N. Prescott Factory for Adamswear The Central Electricity Workshops 15 at Nuneaton Johannesburg, Fig. 6 by B. Williams Joseph Ash and Sons Multi-storey steel-framed 18 tank production shop buildings in South Africa, by C. McMillan Architects: for both projects: Harper Fairley Partnership Local reports summary, 21 by J. Hannon

Composite frame and 25 metal deck construction, by I. MacKenzie Precedent and intuition in design, 26 All the papers in this issue of by J. Roberts The Arup Journal have been taken from THE ARUP PARTNERSHIPS' Industrial building: 30 Structural Steelwork Seminar which was Report from Birmingham, held in London, 8-11 November 1982. by R. Greenwood and P. Handley

Front cover: Victorian steel-the Forth Railway Bridge (Photo: Eric de Mare) Fig. 7 Samuel Heath and Sons, Back cover: The Papal Cross, Phoenix Park. Dublin (Photo: Harry Sowden) redevelopment of existing site. Architects: Kineton Design Group/ Bateman Associates (2) That in the eyes of many specifiers, against concrete. In recent times, for a The structural contractors and clients, there are many period of more than 20 years until around obstacles to the use of steel. These range 1975, demand for steel products exceeded steelwork industry: from long memories regarding supply steelmaking capacity in most parts of the Schemes on the drawing board at this problems, lack of understanding of the world, and certainly in Europe. One gets the moment include a further project at Coventry A review scope for savings in time or material, to impression that the most lucrative markets of a 30m span where a welded angle truss difficulties which exist in obtaining good for the steelmakers were the ones that took will be used and a 64m x 45m building where Richard Haryott advice on steel design. the biggest volume of simple steels, namely portal frames of 15m span have proved most (3) That designing in steel can only be ship building, the motor industry and heavy suitable. successfully accomplished if the task is engineering generally, and as a result supply Conclusions seen as a part of the whole: that is to say the of steel in the form of sections and other To summarize, our recent experience has Introduction contract procedures, the fabric and finishes structural shapes was never adequate. shown: Delays in steel supplies were certainly seen My task is to paint a general picture of the in relation to the structure, speed of con• (1) Buildings must be adaptable for future as the rule, rather than the exception. structural steelwork industry today. struction, fire protection and so on must all planning and flexible for future extension. I am going to concentrate on the situation be part of the evaluation. This may sound Sometime around 1975 the world supplies (2) Roofs must be strong enough to carry concerning the role of steel in the market obvious, but in fact it seems to me that much scene changed. The steelmakers, or the adequate services. place, and in the main I will also be concen• of industry is not tackling the task as a politicians, or both, appeared to get it wrong. (3) Truss or Portal? We will usually trating on those aspects relating to the use whole. In the UK for example, a grand expansion of of structural steelwork in multi-storey examine both schemes but trusses more A key must be education. There is nothing steelmaking capacity had been made, taking often offer the best solution. frames, in one-off special structures where magic about designing steel, but the capacity for production of liquid steel to (4) Bolted or welded trusses? Shop-welded reinforced concrete is a successful or even standard of education and training must be something in the region of 30m. tonnes per with site-bolted joints for almost all projects. dominant competitor. improved if excellence and value for money annum, and at that with no real changes in trusses had to be replaced with new with the universal columns/universal beams Clearly the review is made through the eyes are to be attained. Arups should examine productivity. In Europe capacity increased, monopitch trusses. Parallel lattice girders booms ideal for carrying local bending and (5) Grade 43 or Grade 50 steel? Most of an Arup engineer who is based mainly in what their role should be. and the new steelmaking plants were were used with structural T booms to which the tubular bracings efficient as long struts. schemes have used Grade 43 only but we London. In the time available it is obviously Background market conditions opened up all over the developing world. This angle bracings could readily be welded on To allow for transportation the truss is to be must bear in mind that the same mill delivery not possible to refer to all the many Steel sections have been used in all at a time when the post-OPEC price alternate sides. site bolted with Grade 8.8 bolts. of four to six weeks is offered. We should shocks were slowly reducing world demand therefore look for out places where Grade 50 differences in circumstances worldwide, but construction for over 100 years and for many Another form of truss construction we use We are finding that Grade 8.8 bolts have and helping to bring about major recession. can be used to advantage such as heavy nevertheless it seems to me that there are years the materials held a predominant has universal column or beam booms with largely replaced HSFG on most jobs as they loads on 'short' spans and for certain many areas of common experience and position in bridgework and in major building Suddenly world demand for steel products tubular bracing. The example is a 30m span are easier to use on site. Particularly with bracings. interest. frames. Competition from concrete and fell far short of capacity. Steelmakers in the with warren bracing. overseas jobs we avoid having two bolts of One of the purposes is to propose to you the other materials gradually reduced its market USA are working at less than 40% of their This same principle has been used for the the same size but different grades. Some (6) Grade 4.6 or Grades 8.8 bolts? Almost following main points or themes: share, but nonetheless the industry as a capacity, and in Europe the average output is boiler house at Telford District General trusses for Africa (Job 8399) were all M16 bolts are Grade 4.6 but M20 and M24 (1) That market forces are now such that whole did not seem to run into a feeling of around 60% of capacity. In the UK the BSC is Hospital (Job 4623) of 16m span and 9m transported in containers as individual angle in Grade 8.8 are frequently used for major steelwork is once again a sensible and decline until comparatively recently. currently producing around 10m. tonnes, and high. The initial design for a portal frame members and completely site bolted. The structural connections. economic alternative in many of our 'main• Steelmakers worldwide found themselves in the private sector production brings the total was abandoned when 10 tonne coal hoppers M20 and M24 bolts were grade 8.8 with the (7) Bracing members angle, rod or square stream' structures in areas where concrete a sellers' market for a considerable period of to around 14m. tonnes - pretty much in line had to be carried from the roof and a full M16 bolts in grade 4.6 to avoid any possible hollow sections? All are used with the has perhaps been dominant for the past two time, even if parts of the market, such as the with the capacity/demand situation for the height walkway above the hoppers. The confusion on site and we try to follow this advantage taken of square hollow sections or three decades. construction industry, were losing a battle EEC as a whole. welded steel truss met these requirements procedure in the United Kingdom. for long slender bracings. THE ARUP JOURNAL

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- JULY 1983

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