l i THE ARUPJOURNAL I I I

MARCH 1973 Vol. 8 No. 1 March 1973 Contents Published by Ove Arup Partnership THEARUP 13 Fitzroy Street, London. W1 P 6BQ

Editor . Peter Haggett Art Editor : Desmond Wyeth FSIA JOURNAL Editorial Assistant : David Brown Investigations 2 of structural failures, by P. Beckmann

Linear air distribution 6 principles and practice. by K. Aldridge

J. G. Strydom Tower. 10 Hillbrow. Johannesburg. by R. Finkelstein

Rev iew of awards in 1972 12

Jan Smuts Airport: 14 new terminal buildings. by G. Bottom

Finite element computations 18 of ground movements beneath a trial embankment. by B. Simpson

Front cover: Models of Hillbrow Tower (foreground) Alber1 Hertzog (rear right),and Design and construction 21 innovations: systems Emley Moor Tower (rear lef1) (Photo : Harry Sowden) utilizing panel components. Back cover: Jan Smuts Airport waiting area (Photo: Lynda Shave) by J. Morrish

Gathering evidence with The necessity of formulating Investigations an open mind hypotheses Having started my career by designing building Up to this point. it is as well to keep an open of structural structures. and having lived through a number mind on the cause of the trouble because only of fair-sized contracts. I try at the start of every by doing so will one give equal coverage to all failures new investiga tion to tell myself firmly 'There the available evidence. and failure to do so can but for the grace of God go I'. just in case I mean that some essential fact does not get Poul Beckmann should be tempted to adopt an attitude of recorded in tim e. may be tidied away. and thus academic arrogance towards the original not be available when it becomes apparent that designer or the contractor. one's first hypothesis was wrong. I believe This article is based on a talk given however that before one starts a detailed to the Nottingham Society of Engineers The next thing I try to do is to go and 'view the analysis of anything in particular. one should on 27 November 1972. body' as soon as possible before anybody starts formulate one or two hypotheses on which to tidying up. and in the process. removes some base the further studies. piece of indirect evidence. By this. I mean that My interest in investigating fa ilures is aroused the actual juxtaposition and/or stratification of The ease w ith which computers can process f irstly through my curiosity to find the real the debris. if any. can hold vital clues. For data has led some research worlld d~isel and found that the repair fully effective in re-establishing the whereas the drawings required four 32 mm bars design support moments and thus reduce The case of the missing top bars over the supports. there appeared to be only deflections in the adjacent spans. these had Some years back. I was asked to look at some two 1 2 mm bars across the crack in the whole been jacked up by means of flat jacks which cracks which had appeared in the reinforced width of the beam. were deflated after the repair concrete had concrete beams to the monitor roof of a work- Further probing showed that the four 32 mm reached its design strength. 3 The case of the explain the magnitude of the crack and in addi­ cracked diaphragm wall tion. there was a discrepancy between the Hopper During the excavation of the basement under a measured steel strain and the crack width. the tall block in the City, single horizontal cracks latter suggesting a much more alarming degree appeared on the insides of some diaphragm of overstress. walls. At the time. the intended use of the This discrepancy between strains prompted diaphragm walls as part of the permanent one of my colleagues in the firm to the works was a fairly novel feature and the depth thought that the behaviour of the wall was and sequence of excavation were also outside similar to that of a prestressed beam with the traditional experience. so that considerable unbonded tendons. We began therefore to sus­ concern arose from the appearance and subse­ pect the bond between the reinforcing bars quent widening of these cracks. and additional and the concrete which had been tremied into reinforcement was provided in vertical chases the slit trench which was filled with bentonite cut in the walls. mud. and we instigated a number of tests to Chute for discharging prove our hypothesis. Bentonite Two model beams to one-fihh full size were slurry made and tested ; one beam was cast in a dry mould and the other under bentonite. both by means of a tremie -pipe. The test load was Soit unct.r don.et hne ...... ec1 pno< 10 applied by small. close spaced. hydraulic jacks. simulating the triangular distribution of soil ---- =:;no ol 3'650m / pressure. and five dial gauges were provided to --, measure deflections. ', + 3·650m ', It was found that the maximum deflection of the beam cast under bentonite was 60% greater than that of the 'dry' beam and. in Single crack appeared heft dunng excevatk>n u~ 3'650m addition. the deflected shape of the bentonite tk>of down to 4·250m beam had an acute 'V' shape whilst the 'dry· - 2·750m beam exhibited the normal rounded sag. - 4·250m ------r -- This was a strong indication. but as pull-out tests prior to construction had indicated no substantial reduction in bond of bars dipped in bentonite mud. we felt that further proof was - 9·750m required. -~ We therefore had a block approximately 0.9 m x 0.9 m cut out of the 0.8 m thick wall by means Fig. 4 of thermic lancing so as not to disturb the bond Construction sequence and crack position of the embedded bars by vibrations from pneu ­ in diaphragm basement wall matic drills. The block was taken to a stone­ mason's yard in South London where two beam The phenomenon was however still mystifying Position of 100mm and. to check the stresses in the original re in­ forcement. a bar was exposed adjacent to the crack and had Demec studs glued on to Fig_ 5 right it. After reading the Demec strain gauge Section through formwork and Tremie between the studs. the bar was cut outside the and. below. detail of test panel gauge length and a second read ing gave a release of strain which corresponded to a slight Fig. 6 below i11t1 ( :~~rr ·· overstress in the bar prior to cutting. This over­ Above. deflections of test beams: below. test stress was however not nearly enough to beam with loading points and dia l gauges ~ r 1.. 380 mm .1 f . ~rn~,_. ·.• .· -~--~11 ~ - ·~ :;:_· • ...

Fig. 7 Specimen beam. cut from diaphragm wall. in test rig Fig. 8 End of test beam 2·75,n,n from dia phragm wall in test rig

No Benton,11 ---­ With Ben1on,1t ------

SuPOO

5 Background of the header box or duct which feeds them. Linear air The name ·coanda' is now becoming common Consequently it may be in order at this point to so perhaps a little explanation may help. remember that air is subject to the laws of fluid distribution: Henri -Marie Coanda. a Rumanian. was born in flow and that the design of all ducts and Bucharest on 6 June 1885. His qualifications headers must be based upon Bernouilti's principles and include a doctorate in engineering with degrees theorem which states that : in aero-engineering. electrical engineering and In any body of flowing fuid. in the absence of practice refrigeration. He worked with the Bristol Air­ friction or other work effects. the total head is craft Company in the early years of this century. constant along any stream line. Ken Aldridge His work on fluid flow across deflecting mem­ Put into the form of an equation : bers contributed to the development of the P, V, 2 P2 V22 This paper was first published in the November aerofoil and it was from this that Coanda dis­ Hr = - +-+z, =-+-+Z2 p 2g p 2g 1972 issue of The Building Services Engineer. covered the phenomenon of a fluid in motion the magazine of the Institution of Heating and naturally tending to cling to a solid surface and where Hr = total head Ventilating Engineers. to change its direction in relation to that surface. P pressure at a given point in the This phenomenon can be visualized by remem­ airstream Introduction bering how a jet of water from a tap. although V velocity of the airstream Most products are developed to satisfy a need having a force and direction downwards. will g acceleration due to gravity and so it has been for air terminal devices. from immediately run down a person's arm if the Z elevation above datum the very basic mesh to conclude an air vent or hand only touches a small part of the water p density of the fluid. duct to the more sophisticated square. rectan­ stream. It is this natural attraction of a fluid in It further asserts that the dissipation of work gular or circular diffuser. motion to cling to an adjacent solid which is through friction reduces the total head and the With standards of comfort increasing, the need called the Coanda effect. receipt of work (as in a fan or pump) increases came about for a terminal device to handle As the fluid attaches itself to the surface. the the total head. Consequently the equation may fairly large air quantities at low noise levels and top layer of the fluid begins to slip over the front be re-written as: provide the best possible air pattern. especially of the stream as the lower layer is reduced in P, V, 2 P2 V2 2 when supplying cold air with temperature -+-+z, W+-+-+Z2 speed by the friction between it and the surface. p 2g = p 2g differential up to 11 °C. This was answered by With the slipping of the top layer a negative where W the head loss (or gain) between the linear diffuser. which was initially produced pressure is produced which pulls down the top = points 1 and 2. in America. These diffusers have now been layer nearer to the solid surface and the whole available in this country for many years with all process is repeated once again. This results in Since head multiplied by density gives pres­ shapes. sizes and designs to choose from. the fluid stream thinning out and for a certain sure. multiplying both sides of the equation by With the advent and general acceptance of period during the process the velocity of the p gives: open plan design. the demand in terms of fluid is increased quite substantially. The veloc­ pV,2 pV22 supply and technical performance for this type ity increase is simply due to the normal mass P,+29+ pZ,=W+P2+ 2g + PZ2 of terminal device has increased. In fact. for flow laws being followed (see Fig. 1 ). where P is the static pressure SP. pV2/2g is the any good quality air conditioning design. linear Coanda used the creation of the negative pres­ velocity pressure (VP) and pZ the elevation diffusers are becoming the rule rather than the sure to obtain the nec~ssary lift of the aerofoil term. exception. It is the intention of this article to section whilst others have continued to deter­ If we are dealing with a horizontal duct pZ, = outline the basic principles of linear air distribu­ mine the optimum shape for a maximum rate of pZ2 and cancels. so we can rewrite the equa­ tion and describe the flexibility of this system. change of direction of the solid. in relation to especially the most successful vane controller tion: the original position of contact. without the SP, +VP,= W+SP2+ VP2 designed on air flow principles utilizing deflect­ fluid stream and the solid surface parting com­ ing members. particularly the Coanda surface. pany (see Fig. 2). If we consider a length of ducting of constant For air distribution pu rposes the aim is to keep Tap-ofl...... the mass flow/surface area rat io of the supply c:we,boucwn~ / air as small as possible. This will ensure good -~---..:::..- --- control of throw and drop and provide vertical --:------air patterns commensurate with comfort condi­ - ) ------Solid Mace tions. The linear air diffuser can provide all this. especially the type having the control vane \ ..... o1._... ,,...... ,. designed on the optimum rate of change of direction. Similar results can be achieved by Fig.1 flat vanes. but pressure drop is increased and ( flexibility is reduced. A single slot diffuser with the specially designed deflecting vane can be seen in Fig. 3. A full 1 80° range can be chosen by simply adjusting the vane. One of the important aspects of this 180° air turn is that horizontal air throw can be achieved. Fig. 4 With the average type of diffuser. whether linear or otherwise. to obtain horizontal pro­ jection the ceiling is used. again in the Coanda fashion. The comparatively thick wedge of air emanating from the diffuser is lifted towards Ra1e ot chanve ot sohd the ce iling and reasonably good comfort con­ ...... _ -N~40 1u,tace too tast to, 111.Hd ~~F'---~.....,---+_....._ 11,,am 10 ,em11n 111ached ditions can be maintained with an 11 °C supply Sele<:1,on005i~=::::;;;::=:==~~:::...... =~+-- air differential. However. with the use of many 0-045 types of coffered ceiling arrangements and the 1------1 like. there is no ceiling on which the air can

cling; this results in dumping. With this opti­ 0-03 mum guide vane shape. the air is turned 90° and remains in that direction with or without a ~0225 ceiling surface. Fig. 2 By the time the air has turned to a horizontal position it has thinned out to nearly 1 mm in 0-015 thickness and may be travelling as fast as 60m/s without the noise level being above N R35. This very thin wedge gives the low mass 1·0 flow/surface area ratio of supply air that is D.,c1YN)Clty 1·5 S-0 6-0 7-0 required and. because it is thin. early tempera­ ~v pre:an1·5 2·5 4-0 15·15 2:Z.5 31 ture equalization takes place and air movement is maintained by the force of the supply air Honlontll throw rather than by the density difference (Fig. 4). (with Of without a ceiw,,g) Performance Fig. 3 The performance characteristics of linear dif­ Fig. 5 6 fusers are inseparable from the characteristics cross-section. along which air flows at a con­ (i) The snap-on duct type is shown in Fig. 6. stant velocity, then the energy dissipated by the The sizing of the duct in this application still air in friction at the duct walls shows up as a requires a minimum TP/VPratio of three and for loss of static pressure between points 1 and 2. ducting economy it is usual to let the ratio rise This has led to design principles being stated Ar,y-ojduct ,,., be used to to approximately 10 and then reduce the duct in terms of static pressure loss. In actual fact. size to give a TP/VP ratio of four or five and the loss is one of total pressure. and design ""' then allow once again the ratio to increase as methods utilizing. for example. static regain still the volume of the air in the duct reduces. The involve a total pressure loss : all that is achieved maximum overall length is often determined by is a more suitable balance between the static the maximum siz e duct that can be handled. and velocity pressures if the elevation term is For an example on sizing take the requirement neglected. of 0.5 m3/s to be dis tributed along a diffuser When designing header boxes and ducts for 10 m long with the entire length active. This use with linear diffusers. it is important that a gives 0.05 m3/s per metre run which we can correct balance between static and velocity assume will give us our required noise level pressures is ma intained and the most satisfac­ and throw. tory way of achieving this is to use the ratio of The performance curve shown in Fig. 5 gives the total pressure {the sum of the static and Fig. 6 an initial total pressure requirement of 30 N/m2: velocity pressures) and the velocity pressure as therefore our first duct size can be determined. a criterion of correct balance. since our maximum duct velocity must be com­ puted from the maximum velocity pressure. The performance characteristics for a typical usually sets about the task by analysing and equal to one-third of the total pressure. which linear diffuser are shown in Fig. 5. These curves computing all types of heat gain and loss to a is 10 N/m2. Th is gives a velocity of 4 m/s and a are for a single slot T arrangement having a space, so that the space can be controlled to duct diameter at entry of 0.385 m. 20 mm air diffusion slot. within predetermined limits relative to the Considering a particular air volume per metre financial resources available for the system and The next step is to determine where a reduction run of diffuser. it can be seen from the diagram the function to which the space is to be put. in duct size can take place. Although it is that constant horizontal pressure lines exist From this the air volume can be obtained and normal to reduce the siz e when the TP/VP over a certain velocity range within the header w ith complete knowledge of the building and ratio has increased to 10. it is as well to look at -box or duct. This is the most stable position. As the proximity of the proposed plant room. the duct lengths. manageable segments of ducting the constant pressure lines curve downwards. type of air transportation can be decided. rang ­ and installation ease as well as duct economy increasing variation in the air distribution rate ing from high to low velocity. rather than keep to a specific ratio. along the slot can be expected. If the design Other requirements that must be known or Assuming that in this instance the best com­ point falls below the end of the constant pres­ assumed before selection can begin are : promise is 1 O. then we can proceed and deter­ sure line. part of the slot will not be utilized. (i) maximum supply air to room air tempera­ mine the second duct size. For simplicity of It can also be seen that as the design point is ture differential for cooling calculation and because the duct velocity is moved along the horizontal part of the constant extremely low. it is easier if the friction loss (ii) Maximum background noise levels accep- pressure line. varying velocities can be obtained. along the ductwork is ignored and that our table from the air conditioning system together with a variation in the regeneration total pressure along the complete length of the noise level. (iii) The method of linear distribution. duct and diffuser is taken as constant. There­ Most manufacturers· performance curves are Item (iii) is the decision that is often guided by fore the velocity in the duct when the TP/VP based upon a certain set of standards. Care the financial aspect and the architectural is 10 is = 1.28 -y'TP/10 which gives 2.2 m/s should therefore be taken on the selection of involvement in the scheme. The aesthetics of or 0.25 m3/s. the equipment. and the variations in the stan­ the space to be air-conditioned are not usually Thus. by bringing back the TP/VP ratio to dards that mustoccurfor a specific design must in the hands of the engineer. The resulting five. we require a reduced duct diameter design is often a compromise between the be taken into account. Quite often correction 4x m3/s factors are provided. but. for guidance. the technical advice and the architectural consid­ ~---- ~ 4x 0.25 = 0_32 m main set of standards generally used is given erations. closely followed by the financial side. 1 .28 rrvfP15 1.28 rr,v30!5 below: Some of the considerations are : (i) Standard air (ie. barometric pressure. etc) (a) Any ceiling module that has to be adhered This can be carried out until the complete (ii) Throw rate of a particular length and size to length is sized. If the duct reductions do not fall easily, then it is a simple matter to start of slot (b) The anticipated lighting layout and type of along the duct run once more and manipulate lighting fitting (ie. recessed. flush. etc.) (iii) Throw rate for a particular air terminal the TP/VP ratio as necessary. Balanced con­ velocity (c) Width of air distribution slot acceptable ditions will always exist providing the TP/VP (iv) Throw rate for a particular direction of (d) Does the architect require a completely ratio does not fall below three. throw (ie. horizontal or vertical) clear ceiling for architectural freedom? (v) Room air to supply airtemperature differ­ ( e) Linear air slot part of lighting fitting-walls. ential (positive or negative) partitions. furniture. Low ratlO ( 3 ) Htgh ,.,io 00•) (vi) Type of header duct inlet (ie. centre-fed Most problems of this sort are peculiar only to 90' or end-fed) the project under consideration and although (vii) Regeneration of noise levels based upon there are a considerable number. most can be specific acoustic room absorption. dismissed in the general design process which Fig. 7 Most of these variations do follow mathema­ should then leave a solution which is practical tical laws. but it is as well to consult the manu­ to both the architect and the engineer. How­ facturer concerned if any doubts exist. ever. the initial choice of linear air diffuser lay­ outs is generally made by the eng ineer and The air pattern or direction of throw relative to When a design point has been selected for a eventually given to the architect for approval. the duct axis will vary slightly with the TP/VP specified air volume rate per metre run and a If the architect does not favour that particular ratio (Fig. 7). This can, of course. be used to specified noise level. consideration must be some advantage but generally does not affect given to providing the correct air pressure and solution then a compromise will have to be carried out. This method of approach may seem the overall room air pattern. With the ratio at velocity coming onto the diffuser. The total three. the direction of throw is approximately pressure indicated from the curve is the most rather long-winded. or indeed unnecessary, but as air terminal devices play an important 60° at the duct axis. gradually straightening to important aspect and must be used as a basis 90° at a ratio of approximately 1 5. for any duct sizing. Details are given later for part in the appearance of a design. a little time each type of header arrangement, but as a in this direction may save quite a number of (ii ) The header box can either be a standard general rule the total pressure/velocity pressure redesigns all the way back to the plant room. manufactured box or one designed by the ratio must always be more than three to main­ Header types engineer as in Fig. 8. For small air volumes tain balanced conditions. Therefore. so long as Regardless of the way the air is taken to the the total pressure requirement is adhered to. space to be controlled. the final delivery to the variations in velocity. which might be imposed linear air diffuser must be related to the condi­ by space limitations. can be tolerated. tions required in the room. However. the Aesthetics method of connection to the diffuser can be Once the decision has been made that linear air varied to suit the ceiling void depth and to a distribution is required for a particular project. certain extent the supply air pattern. There are certain basic steps of design selection should three basic methods : be taken. not only to achieve t he optimum in snap-on ducts performance. but also in economic terms. header boxes Fig. 8 In designing an ai r conditioning system. one and pressurized voids. 7 standard products should be available. but fibre. wood fibre and metal ceiling tiles have sensible gain or loss. The motor can regulate once the air volume to be handled becomes not been designed for this application. except the quantity of air in relation to the internal excessive or unusual space limitations exist. for ventilated types. surface temperature so that down draughts are then headers have to be specially designed. The air leakage through some types of tile is prevented and the local air temperature main ­ The sizing principles used on the snap-on duct quite considerable and care should be taken in tained. This method has been used on a num­ still apply; the only difference is the shape of tile selection otherwise results in air distribu­ ber of projects quite successfully. the duct or header. Quite often the void space tion may be disappointing. Some manufac­ High air-change rates allocated for services is extremely small and turers now provide the facility to seal the tile The linear diffuser system can handle most air this is sometimes aggravated by low noise by applying a metal foil to the back. It is also change requirements. Projects have been suc­ requirements. recommended that a concealed fixing ceiling cessfully designed for computer suites with air system is used to limit still further tile edge change rates over 120 per hour. leakage. The air pattern from this application is The most common method of distributing the similar in every respect to that described for the air in computer suites is the perforated ceiling snap-on duct. There is no particular limitation system using a positive pressure void. Air is - ~e-,ecu::ng in the length of ceiling from the supply duct ; then extracted at low level. or in floor grilles if a plate Of fitter medium good results have been achieved up to 35 m. suspended floor has been installed. Whilst the One point to bear in mind when designing the perforated ceiling system functions extremely Fig. 9 system is that very often the ceiling void has well in this and other applications. it will only obstruction such as beams, lighting fittings and work well if the extract point is at low level. possibly other ducts. so the limiting velocity High level extract points can cause short cir­ Should a header duct be reduced in size. this (for the correct TP/VP ratio) must be at the cuiting due to the natural convection currents. w ill obviously produce a higher velocity pres­ greatest obstruction passing the greatest from the areas of high sensible gain. being sure than is actually needed. Therefore to main­ amount of air. higher in pressure than the air supplied from tain balanced conditions the total pressure Horizontal air patterns the ventilated ceiling. must also increase (see Fig. 9). The result will be to increase the noise level which originally Linear air distribution gives its greatest flexi ­ If it is not possible to have a low-level extract related to the selected volume flow rate per bility in the type of air pattern and positions of point, the pressurized void system can still be metre run of diffuser. To overcome this diffi­ supply points that can be used. used using the linear diffuser. The void acts as culty. the header duct and the top of the diffuser Arrangements usually comprise a series of the header duct and the high air volumes can can be separated by a perforated sheet or filter linear diffusers stretching across the room. be handled by lapping the air streams as shown medium to absorb the additional pressure. The corresponding to a building module. a ceiling in Fig. 12. The high air velocities used ensure sheet should be used if only a small pressure tile module or lighting layout. This is done to that good balanced conditions exist and will drop is required. whilst for high pressure drops achieve a neat appearance which· often means not be affected by the position of the extract of up to 370 N/m2 a filter medium may be that there is more diffuser slot available than is points. chosen. With the filter medium. it is then worth­ actually necessary for air distribution. Thus a Variable volume while to include a secondary filter in the main choice is available for the position of the active When a variable volume system has been duct system to ensure that the air passing air sections which can be chosen at the com­ chosen. troubles often occur at points of mini­ through the linear diffuser is as clean as pos­ missioning stage when greater knowledge of mum volume. causing certain areas to become sible. Furthermore. in the event of space con­ the positions of high sensible heat gain. due to stagnant. whilst others suffer from drop. To trol being especially important. an alarm signal machinery or occupants. are known. overcome this using conventional square or on the secondary filter when the pressure drop circular diffusers. the number of diffusers has rises to a certain limit is advisable. Without this to be increased to give good coverage and to precaution there will be a gradual decrease in limit the range they have to handle. This results the air supply as the secondary or linear filter in a very messy ceiling arrangement with extra medium becomes clogged. expense involved. both in terms of equipment The horizontal air pattern for the header box and labour. behaves in a similar way to snap-on ducts if Since the linear diffuser has a very low volume/ the run is continuous. With the small standard surface area ratio. its coverage of the space to plug-in boxes. however. the air pattern corres­ be controlled is extremely wide. Also. with the ponds to the shape of the box itself. With slop­ diffusion vane having a Coanda surface. no ing ends the air pushes out at an angle whilst drop of the air will occur at any point between for a square box the air distributes at right 0 and maximum air volume. Moreover. if indi­ angles (see Fig. 10). vidual air patterns are designed to overlap at Fig.11 maximum volume and meet at mini mum. volume. complete coverage of the space is achieved at all times (see Fig. 13). 0 Fig. 11 shows a simple arrangement of linear ~-,1ev-.,-..,--~- Ce..,g-~--,/ ,..-.-,.,.---0 "'~- diffusers. The total lengths of diffuser often have the vane controller split down into

Plan ..... ol 300 mm sections which enables the supply air honzcnlal.., direction to be staggered. The air patterns palletn "-'° shown are for horizontal projection. oc,era1e vane ,' " .. ,. Occasionally. a design may requ ire that the air ·r-.. -<__ shall be supplied from one side of a room. pos­ Curtain --l.g'fCngf11i,,g Fig.10 sibly because the architect or interior designer Walo,~ wishes to create a special ceiling which is in no way linear. This can be achieved quite easily for ~ ---. - (iii) The pressurized void system is extremely air throws up to about 20m with a limiting NR . popular when minimum space exists within a of 35 . With this type of supply the comfort con­ ceiling void and the lighting load or sensible ditions are in no way reduced. in any part of the gain to the ceiling void is small in relation to room. from the high standards that are obtained Fig. 12 the total sensible gain. using a symmetrical distribution. The ceiling void itself acts as a header duct. but The volume flow rate per metre run requirement to ensure balanced conditions over a number is greatly increased. but the problem of noise is Velooly025,rp solved. by using a multi-slot arrangement as in of linear diffusers within the ceiling, the veloc­ 'fhrow.., IO()SIIIOf'I$ ity pressure at the first diffuser. with respect to Fig. 1 2. This method can often create an inter­ fo,m1nmum~ the air flow. must be no more than one-tenth esting edge detail if it is included with a ceiling of the pressure drop across the diffuser. This upstand incorporating a curtain track or light­ ratio has been determined from empirical work ing wallwash. Because the thickness of the air and applies whether the ceiling void is used for emanating from the slot is thin. with a multi­ supply or extract purposes. So long as·the ratio slot arrangement it is possible to layer each air is one-tenth or less. the system becomes self­ stream so that collision and subsequent down Throw PC)SltlOr'IS balancing and the performance figures of the draughts do not occur. tormax,m.mvoune , particula r linear diffuser apply. the only differ­ One technique developed from the multi-slot \leloo(V O 25ml, / ence being that the header duct has been arrangement is to motorize the air diffusion removed and the TP/VP ratio increased. vane nearest the wall or window if that wall or The use of the ceiling void for air distribution is window is contributing a high heat gain or loss fairly new in comparison to suspended ceiling to the space. The air supply on that one slot can Fig. 13 8 systems and therefore normal types of mineral be directed towards the wall and counteract maintain a specific background noise level. but controlled zone the dead zone can be classified if a building is designed to keep out the noise it as part of the extract system. even though there 90 has to be relatively airtight and therefore mech­ may be some sensible gain from the lighting 80 anical ventilation or air conditioning is installed. fittings at high level (see Fig. 16). This system Therefore. the air distribution equipment can be will also work well with a low level extract. 70 ~ selected to provide the necessary background Other uses ~ 60 noise level. This can be obtained and regulated The use of linear diffusers can have other ~ from the regeneration of noise that occurs as 50 advantages. With a double inverted T ceiling the air passes through the diffuser. It is recom­ arrangement many other applications are avail­ 40 NASO mended that. if this method is going to be used. NA 45 able to the architect or building services engin­ i0 NR 40 30 the volume flow rate per metre run and air pres­ eer (see Fig. 17). The T can be used for: NA 35 sure rating be chosen so that the noise level for a NA30 20 the duty is at least 3 N R lower than is actually (i) Supporting of electrical power and the sup­ NA25 port of lighting fittings 10 NR 20 required. Also. the performance point should 63 125 250 500 1000 2000 4000 8000 be favourably balanced. Alternatively, the (ii) Location for partition heads FFIE.OUENCY · Hz length of linear diffuser required to handle the (iii) Supporting sprinkler heads or smoke The heavy curve shows the level of regeneflllOf'I 1NR 35) tha1 occurs wtlh 12mm required air volume should be about 20% detectors IIOt ina hnea,ddfuserunder"" &r p,es.!Ue of 42 NP''ho14') orv.-.g 0·5m1/s This more than is required. This ensures that for C\IV8 can be mo,,ed upo,doiNrlby changlog lhe volumo flo\N rate OI' dampe,ing (iv) Different ceiling systems with varying 10 gve a ~r back pressure the same design header pressure the volume linear extrusions (ie. concealed grid or flow rate per metre run is reduced if all the laying grid system) diffuser remains active. thereby reducing the (v) A ceiling void extract system. Fig.14 noise rating. The margin in noise level allows for any discrepancies that may occur in the acoustic design in relation to the acoustic environment that is eventually built. Thus a positive or negative tuning of the background noise level may be carried out at the commis­ sioning stage to suit the actual conditions. With the Coanda diffusion vane the sound spectrum of the regeneration follows closely the NR lnac1,ve sec1t0n achieved by aampenng curves. This gives much better control of the us,ng con1rol van~ acoustic environment. especially if masking is Smoke detectors or spunkier ~I required (see Fig. 14). For an example. consider a room requiring Fig.15 0.5 m3 /s. having a background noise level of NR 35. The performance curve shows that an active distribution of 0.05 m3/s per metre run is required and therefore a length of diffuser 10 m

long. For this exercise. if we size on 0.05 m3/s Lay-in grid S)'S1em Corcealed s,.d syslem per metre. but install 20 m of diffuser. this Cetfng svstems allows for 50% of the installed length to be shut off (Fig. 15). If the performance point selected is perfectly stable. it is possible to shut off or open other sections of the diffuser on site Retu,na., within a range and thereby change the regen­ erated noise level. up or down. without affect­ ing the total volume of air that is required to be supplied to the room. Within the range the air throw will vary only slightly. Re1urn., baffle for negative VOid e,nract. Acouscic 1rea1men1 prOllides good allenuBIIOO High ceilings Fig.16 With air conditioning systems being installed Fig.17 in old or lofty buildings. it is sometimes found necessary to move the total volume of the room air to maintain conditions. With a ceiling height Tuning from 6 m upwards. ceiling air supply becomes Where cross-talk is a problem and a common Now that the era of glass buildings is slowly diff.icult and supply from the sides is limited by void extract system is used. the static insertion disappearing. some buildings are being length of throw and drop. with the result of loss can be improved by fixing a return air baffle designed to give an ex_ternal fabric sound very uncomfortable air movement and temper­ lined w ith a fibre glass mat. This design will attenuation around 45dB to nullify the noise­ ature variation within the space. give a room to room attenuation of around polluted atmosphere that occurs near airports. One way to overcome the problem using a 35dB. providing the ceiling syste·m and parti­ high density traffic areas. etc. With open plan Coanda linear device (if a suspended ceiling is tions are of the correct standard of construc­ offices and the high degree of soft furnishings, not being used) is to throw the air from the tion and installation. the acoustic atmosphere. between the passing sides and cover the completed area of the Acknowledgement of aircraft or a lull in the traffic. becomes dead space. This then creates a dead zone above the The author is grateful to Peter Platten for con­ and feels uncanny to most occupants. air pattern and enables only the air below to be structive suggestions made during the prepara­ Sophisticated electronic noise can be used to controlled. If the extract duct is above the air tion of this paper.

9 Johannesburg should be constructed. The proportions of the structure were acceptable J. G. Strydom present siting of the tower was necessitated by under the varying conditions. the extensive existing cable system in the area Three further design criteria were important. Tower, Hillbrow, of the present telephone exchange in Hill brow. Firstly. being in a congested site. the available The site chosen. while being technically correct. space to spread the base of the tower was Johannesburg imposed unique problems for the designers of limited. As the tower is governed both by stab­ the tower. Being in a built-up area extremely ility and deformations. it was essential to pro­ Ron Finkelstein prominent in the city, a civic responsibility vide maximum stiffness of the shaft. not only existed to ensure that the structure was both at the bottom. but over its full height. Secondly, acceptable visually and free from contemporary the construction of a structure of this type can Rising 269 m above the streets of Hillbrow, gimmicks which would become dated in the create extremely hazardous conditions for resi­ with the top of its mast almost 2134 m above near future. The tower is thus built to remain dents living in the area. The need. therefore. to sea level, the slender concrete pencil of the prominent and acceptable into the 21 st Cen­ choose a solution which limited the amount of J. G. Strydom Post Office Tower in Johannes­ tury. The area of Hillbrow has a particular movement of free formwork, etc. was extremely burg is the tallest structure in Africa. cha ra cter of its own. consisting largely of important. Thirdly, the tower had to be com­ With the development of high-rise buildings rectangular. tall buildings, and the designers pleted in an extremely short time. in order to on the ci ty landscape. the Post Office telecom­ had to integrate the new tower into this prevent disruption of the city's telecommunica­ munication links to Benoni, Carletonville and environment. Of particular importance is the tion services. Simplicity in form was therefore other stations were being interrupted. It was fact that the tower is masked by the various essential. decided. therefore. that a tower of sufficient buildings at different heights when viewed Based on these various criteria the structural height to position the transmitting antennae from different parts of the city. Of prime import­ solution which now dominates the landscape above the tallest foreseeable buildings in ance, therefore. was the need to ensure that the was chosen. The first stage of the construction of the complex was to complete the tower to house the Post Office equipment. Concurrently the new automatic telephone exchange was com­ pleted. With the main objective of constructing the upper turret in minimum time and to eliminate the hazards of difficult construction at great heights. it was decided to make extensive use of precasting. The two turrets. while being independentstructurally in the completed form. had to be considered as a combined problem during the design and construction phase. The key section of the tower is the upper Post Office turret which houses extensive microwave equipment and this section had to be com­ pleted at the earliest possible time. The solution chosen. therefore. was to construct the skeletal frame of the lower turret in beam and column units. which acted as a bracing structure for constructing the upper turret. At a later stage the lower turret was completed. Basically the structure comprises a reinforced

Figs. 1-3 above and below Various stages in the construction of the tower (Photos : Lynda Shave)

10 concrete tower bu ilt to a height of 232 m and was that the slender nature of this structure preformed system of radial steel beams. One of topped by a 38 m high steel mast. The founda ­ made it susceptible to vibration under certain the most difficult problems was to ensure an tions of the tower consist of eight 3.2m wind conditions. adequate fire resistance in the turrets and diameter shafts sunk to a depth of 42 m. The It was calculated that the whole structure considerable work was done to ensure that a external structure is a free-standing cyl indrical would have a low frequency of oscillation and collapse would not occur if an accidental fire shell, 13.7m in diameter w ith parallel external it was designed rigidly enough to dampen any broke out. sides top to bottom. tendencies for the oscillations to become exces­ Although the public will not be aware of it, the A transition in the structure occurs at 179 m sive. Vortexing was found to occur randomly at apex of the mast on top of the tower will sway where the 11 -storey turret structure begins. various heights on the structure depending on 860 mm underfull wind loading, the microwave The thickness of the concrete shaft at the base the w ind velocity and one of the computer room 480 mm and the revolving restaurant of the tower is 840 mm and then tapers to programs was used for comparing the energy 410mm. This limited sway is essential so that 380mm at the top of the concrete shell. The impulse from the vortex shedding with the the aerial alignment with other microwave service and lift shafts are constructed inside the natural absorption. of energy inherent in the stations remain accurate to the required one­ structural shaft. The six lower public floors in structure. third of a degree. the turret section have an external diameter of Computer programs were also devised for Construction of the tower commenced in 20m. Microwave equ ipment is housed on an checking the wind and eccentric load bending January 1968 and was completed in March additional two floors which cantilever out effects on the tower as a whole and also for 1971. Costing £1,100,000 it has a mass of above the public levels. determining quantities of reinforcement in the approximately 19,050 metric tons. In its con­ To allow differential movement between the outer cylindrical shaft. The usefulness of having struction 9,175 ma of concrete and 1,315 outer shell and the inner core and yet restra in the design on computers was demonstrated metric tons of steel reinforcement were used. plan rotations. a special sl iding joint had to be when the overall height of the tower was The Post Office realized that this landmark incorporated in the transition stage. It was increased at a very late stage. This necessitated could be a great attraction for visitors and has estimated that at the expansion joint there may a complete redesign which was carried out accordingly catered for them. In an imposing be movements of up to 50 mm due to creep and within a few days. foyer a display of photographs and diagrams shrinkage and 74 mm due to temperature fluc­ The inter-connection of the 38 m steel mast provide sufficient information about the tower tuations. The joint allows independent move­ through the lift motor room provided unusual to satisfy the most inquisitive visitor. ment of up to 150mm between the inner and construction details. which were solved by Two high speed lifts carry visitors smoothly outer shells. thus relieving the structure of means of an elaborate frame at the lift motor through the heart of the central ten service longitudinal stresses. room level. Consideration was given to the floors of the tower at 6 m per second, to six In order to reduce the period of construction . erection of the mast by using a helicopter, but public floors, providing a vast window on the the lower turret was constructed in large pre­ it was eventually decided that the time schedule whole of Johannesburg. The panoramic view cast units consisting of columns and curved could be met by means of conventional con- encompasses the famous Witwatersrand gold­ external beam panels. These units were struction. · fie Ids in the south to the sweep of the assembled in advance of the floor construction The construction was carried out under very Magaliesberg mountains in the north. and braced to the tower core. They were then exacting access problems and pressure from The restaurant at the upper level revolves used to support the heavy cantilever construc­ local residents to restrict noise and dust silently once every hour, providing 200 diners tion of the larger diameter upper Post Office nu isance. The contractors worked closely with with an ever-changing view of the city. Below turret floors. which were also made from pre­ the designers and showed much ingenuity in the restaurant is the highest cocktail lounge in cast wall units. methods of construction and in the mainten­ Johannesburg. The public floors are carpeted Particular attention was pa id to the finish on ance of accuracy of the construction. This throughout and air-conditioned to provide these units which is a white exposed aggregate problem of vertical alignment during building maximum comfort at all times. The visibility cast in white cement. was solved by using a helium neon laser rigidly from the public floors, on a clear day. is over Computer programs were used during the fixed at the base of the tower and focused on an 80km. design stage for solving the more difficult upper target. The construction of the cantilever Credits Client : SA Public Works Department. problems associated with wind vibrations and floors and the turret was simplified by the Architect: SA Public Works Department. gust effects. One of the major design problems extensive use of precast concrete and a Main contractor : Christiani & Nielsen.

Fig 4 The completed tower (Photo: Lynda Shave)

11 A review of awards gail

ASSOCIATION OF CONSULTING ENGINEERS OF AUSTRALIA 1972 ANNUAL AWARD FOR EXCELLENCE .Job no. 1112- Sydnay Opara House (glass walls) (Fig. 1) Architecls : J0rn Utzon (Stages 1 & 2) Hall. Todd & Linlemore (Stage 3) Glasswork sub-contractor : Boussois-Souchon Neuvesel, Ste.

CONCRETE SOCIETY AWARDS 1972 Highly commended .Job no. 2798-Crucible Theatre, Sheffield (Fig. 2) Architect : Renton Howard Wood Associates Main contractor : Gleesons (Sheffield) Ltd . Special mention .Job no. 2102- Blackpool Police HQ and Law Courts {Fig. 3) Architect : Tom Mellor and Partners Main contractor : G. & J. Seddon Ltd . .Job no. 2869-Dalston County Secondary Girls School, Hackney (Fig. 4) Architect : Jellicoe and Coleridge Main contractor : Wates Construction Ltd . .Job no. 3429-Emlay Moor Television Tower, Yorkshire (Fig. 6) Designer : Ove Arup & Partners Main contractor : T1leman & Co. Ltd.

DEPARTMENT OF THE ENVIRONMENT GOOD DESIGN IN HOUSING AWARD 1972 Highly commended .Job no. 3017-Garrad's Rd. Old People's Home, London SW16 (Fig. 6) Architect : Lambeth Borough Architects Department

~ ::...... ~ ~ ::E <::.. C: <:: ~ ..,0 ~ l:! 0 0 [ et "'? "'~ ~ 2 0 et !d during 1972 8

FINANCIAL TIMES INDUSTRIAL ARCHITECTURE AWARD 1972 Winner .Job nos. AA152, 170, etc.- lBM Development, ~ Havant. Phase 1, Respond Centre; Phases 2, 3 & it 4, Systems Assembly Plant; Phase 5, Materials Distribution Centre (Fig. 7) Designed by Arup Associates Architects + Engineers + Quantity Surveyors. Commended .Job no. AA126- New offices and works for the Oxford Mail and Times Ltd. (Fig. 8) Designed by Arup Associates Architects + Engineers + Quantity Surveyors .Job no. 3684-Studio for Bernat Klein at High Sunderland, near Selkirk (Fig. 9) Architect : Peter Womersley.

THE RIBA ARCHITECTURAL AWARDS 1972

.Job no. 1976-Birmingham Repertory Theatre, King Alfred's Place, Birmingham (Fig. 10) Architects : S. T. Walker and Partners. in association with J. A. Maudsley. Birmingham City Architect . .Job no. 2062- Ulster Museum, Belfast. Extensions (Fig.11).

Architects : Francis Pym. until March 1968 : after this date the project was supervised by the Chief Architect's .; branch. Works Division. of the Ministry of Finance § of the former Government of Northern Ireland. ~ .Job no. 2798-Crucible Theatre, Sheffield ·"' (Fig. 2) -~ .Job no. AA/ 17S-'Horizon' Project. Factory for -::: ~ .John Player & Sons Ltd., Nottingham (Fig. 12) Designed by : Arup Associates Architects + Engineers " + Quantity Surveyors.

SOUTH AFRICAN ASSOCIATION OF CONSULTING ENGINEERS AWARD FOR DISTINCTION IN DESIGN 1972 Winner .Job no. SA 979--..1. G. Strydom Tower, Hlllbrow, .Johannesburg (Fig. 13) Designed by : Ova Arup & Partners (South Africa). Highly commended .Joh no. SA 2043-Rosslyn Brewery, Pretoria (Fig. 14)

Architects : Powell. Whyte & Partners. Prime agents : Ova Arup & Partners (South Africa).

10

13 Jan Smuts Airport: New terminal buildings, roads and associated landside works Geoff Bottom

Introduction At the beginning of February 1967, Ove Arup & Partners were appointed structural consul­ tants for the complex of new terminal buildings at Jan Smuts Airport. Johannesburg. Such a complex had become necessary to meet the increasing demand for passenger and freight handling facilities at the airport and the brief demanded a tight and exacting schedule. It was essential that the construction programme was so phased that the new passengerfacilities would become operational by the end of 1971. to coincide with the inauguaration of South African Airways' Jumbo Jet service to Europe. The construction sequence for the terminal buildings was divided into five separate con­ tracts to meet the building deadline and. throughout the various contracts. the entire design team was fully extended so as to remain one step ahead of the contractors. However. a close spirit of co-operation developed between the former and the latter as the building work progressed. The designers were thus able to adjust final details to meet on-site conditions and. as a result of this team spirit. the final building deadline was met. The initial building programme comprised a terminal complex for international arrivals and departures at split levels with a separate domestic arrivals concourse. The concept for Flg.1 channelling arriving passengers to ground floor Detail of ornamental fountain on level and departing passengers to first floor forecourt piazza with fac;ade wall, required the incorporation of an elevated supporting elevated motorway in the motorway as an intregral part of the design. background These new passenger handling buildings cover a ground floor area of approximately 1.8 hectares. incorporating a basement over the the firm was appointed consultants was the Variations to depths were made with steel skirts whole area. provision of a 6.8 million litre reservoir and ring added to the bottom shutter pans. Located as an independent tower. an adminis­ water main system for the building complex. The architectural design of the building called tration office block. seven storeys high with Terminal buildings for large volumes of floorspace in the concourse three basement levels. completed the brief for areas uninterrupted by columns and conse­ the initial building programme. The site was officially handed over to the con­ tractor on 1 June 1967 and some 87.000m3 of quently a large proportion of the mezzanine At an early stage in the project Arups were material had to be excavated from the base­ floors are hung from the main floor structure called upon to undertake a detailed traffic ment area before piling could commence. Piles above. These mezzanine floors span approxi­ survey to predict parking requirements at the ranged in diameterfrom 460mm to 1.07 m and mately 11 m in both directions and are designed airport. Following a report to the Public Works something over 1,200 piles were cast to form as 460mm thick two-way coffered slabs with Department. the firm was commissioned. as a foundation to the terminal buildings. All piles ribs 190 mm w ide at 0.9 m centres. principal agents. to provide underground park­ were taken down to refusal on a decomposed A special system of propping the floors during ing accommodation for 1.300 vehicles initially, andesite lava. the construction stages had to be evolved to phase in with the opening of the new term­ The superstructure of the international terminal because of the unusually tall floor to floor inal facilities. The brief allows for the provision heights. the large spans and the hanging of parking facilities for 4,800 vehicles eventu­ building and of the domestic arrivals concourse, together with the two adjoining buildings mezzanines. These props were positioned on a ally, with the extensions being programmed for 2.74 m grid to suit the module of the building construction as and when required. forming the main terminal complex. covers an area of approximately 240 m x 90 m. The and remained in position during the course of The parking garage comprises two levels of international terminal building consists of a construction until the upper portions of the underground parking covering some 2.4 hec­ basement. a ground floor arrivals concourse. a structure were self-supporting. tares of plan area and is linked to the terminal departure concourse at the first floor and a roof 25 mm wide expansion joints running east­ concourses. which is used as a public viewing and waving west and north-south through the complete The roof over the garage forms a paved piazza platform. The head-room of the arrivals and height of the building split the structure into providing a forecourt to a strikingly patterned departures concourses is in both cases 8.2 m. six separate sections and control the expansion fac;ade wall. which supports the elevated Two mezzanine floors are located between the and contraction of the building. motorway to the departure concourse. main floors but cover relatively small portions Approximately 23.000 m3 of concrete were Associated with the parking garage. the firm of the building and. taking into account air­ placed in the international terminal building was appointed civil engineering consultants conditioning services. the headroom in these during construction and 3,000 tons of rein­ for the design of the landside road network areas is reduced to approximately 2.9 m. forcing steel were used. Because of the large serving the terminal buildings and parking The main superstructure floors have spans spans involved. special rollings of steel had to areas and linking up with the provincial roads varying from 8.2 m to 21.9 m and are con­ be ordered. interchange on the western boundary of the structed of reinforced concrete, taking the form The domestic arrivals concourse consists basic­ airport. The brief included all traffic surveys. of heavy main beams supporting secondary ally of a basement, ground floor and roof slab control of traffic flow and parking for the final ribs 230 mm wide at 1.37 m spacings. The with a first floor slab forming a balcony to a airport development. structure was designed so that the same steel large double volume central area. The structural 14 The final aspect of the development for which shutters could be used for varying rib depths. frame is reinforced concrete again with spans Fig. 2 Fig. 3 above Fig. 4 below Detail of strip timber panelling in Detail of in-transit passenger bedrooms Detail of overhead pedestrian link between TV auditorium on roof of terminal complex administrative office block and terminal building constructed with structural steel

in the order of 11 m. The floors are supported by 690 mm deep marn beams and 530 mm deep secondary beams spaced at 1.37 m centres. The roof to the concourse forms an interesting structural component and was constructed as a two-way cottered slab spanning 24.4 m and extending for 45.7 m with ribs at 2.74 m spac­ ings in the east-west direction and 1.37 m spacings in the north-south direction. Elevated motorway to the terminal buildings The motorway on the land side of the terminal buildings consists of a four-level, reinforced concrete structure comprising the basement. a ground floor roadway, first floor roadway with roof above. The upper roadway serves inter­ national departing passengers and the lower roadway the remaining passenger movements. The Porte Cochere portion of the roadway spans 20.1 m and is supported every 5.5 m by the architecturally conceived grille wall which is used structurally to carry the loads down to the foundation level. The upper roadway has approach and exit ramps 9.1 m wide which take the form of a bridge-type structure supported on single cen­ tral columns at 16.5 m spacings. The portion of motorway in front of the domestic arrivals and departures concourses is designed to allow for future remodelling of the old concourse. The structure consists of precast. prestressed. trough-shaped beams spanning 20.1 m onto in situ. reinforced concrete. portal frames with columns at 16.5 m spacings. The complete motorway complex absorbed 20.600m3 of concrete and 3,000 tons of rein- 15 forcing steel in its construction and is approxi­ mately 640m long from the beginning of the approach ramp to the end of the exit ramp. Administration building The administration building consists of three basement levels and eight floors above ground. The building relies upon the central core for its wind stability and the floors are generally of solid flat slab construction. The building is sup­ ported on piles and is designed as an integral part of the parking garage which surrounds it. Underground parking garage The excavation of the two-storey, underground parking garage was started in January 1970. The garage consists of two parking levels below ground with a brick-paved piazza and orna­ mental fountain on the roof. The lower floor of the parking garage is below natural water level. which necessitated a sophisticated under-floor gravity drainage sys­ tem. The drainage system was installed and put into operation during excavation. thus enabling the contractor to work on a dry site. The basic grid of the garage is a 17.1 m by 2.54m module. The garage has been so designed that extension can take place in the future without disrupting the operation of the garage and the existing drainage. electrical and sprinkler services. -, 1 Access roads The road system is designed to cater for traffic arriving from Johannesburg. Pretoria. Kempton Park and the East Rand via the provincial road interchange to the west of the airport building complex. The traffic is directed either to the upper motorway for departing international passengers or to the ground level motorway which serves arriving international passengers and all domestic flights. An alternative route makes it possible to proceed directly to the parking areas both underground and at surface level. Provision has been made for the future when domestic passengers will depart from the upper level motorway as well. The exit roads lead traffic from the terminal buildings and the parking areas back into the provincial inter­ change. Fig. 5 The road system serving the new terminal The roads in the terminal area extend over a buildings also integrates with the roads serving Elevational view of administration length of 7 km. whilst the link road and internal the new freight areas to the north of the term­ office block with double level underground service roads to the new freight complex will inal. The whole internal airport road system parking garage in the foreground be approximately 5 km long. The open-air park­ virtually forms an interchange in its own right ing in the terminal precinct covers approxi­ and the roads interlink through a system of mately 6 hectares. under- and overpasses. The largest of the three Fig. 6 A considerable proportion of the roads is in bridges incorporated in the scheme is a pre­ The public section of the first floor deep cut. and founding conditions at this level. stressed concrete bridge with a central span departure concourses. Note the granite at which poor clayey material and the natural of 29.3m. finish to columns watertable were encountered. presented prob­ lems both from a drainage and strength point of view. These roads required a depth of con­ struction of 0.9 m with excessive subsurface drainage in the lower areas. It was obvious that the construction of these roads and other services in the area would have to be very carefully staged and programmed to fit in with the construction programme of the new terminal buildings and the new under­ ground parking garage. Access to and from the airport had to be maintained at all times and many deviations were necessary for all the new roads to be built through existing routes and parking areas. As existing parking areas were drastically reduced to allow new construction to proceed. new parking areas had to be made available. Full account had to be taken of the Provincial Administration's programme of construction for its highway and interchange outside the airport. which also included extensive devia­ tion works. and the airport roads programme had to be phased in with this work. A detailed procedure chart thus formed an essential part of the tender and contract documents for the airport roads system. This predetermined pro­ gramming was a major feat of engineering planning and was highly successful in ensuring uninterrupted flow of traffic throughout the 16 construction period. Water supply and fire protection directly into the Kempton Park system. A separ­ year followed shortly afterwards by phase two Water for domestic and fire fighting purposes at ate 375 mm diameter connection takes the of the roads contracts including three bridges. the passengerterminal and freight complexes is sewage from the new freight buildings which The final handover of the roads contract will stored in a 6.8 million litre reservoir from which also house the new flight kitchens. have to phase in with the completion of the it is pumped through 300 mm and 350 mm steel Conclusion provincial road's interchange. ring mains. These mains are bitumen-lined and At the time of the inaugural SAA Jumbo Jet However. work is now proceeding on the two wrapped with bitumen-impregnated fibre flight to London on Friday. 10 December 1971. new freight complexes at Jan Smuts. one for glass. and joints have a moulded bitumen cas­ more than three-quarters of the terminal build­ SAA and the other for foreign carriers. The firm ing. The pipes are further protected against ings had been handed over to the Department is involved as consulting civil and structural electrolytic corrosion by means of an impressed of Transport as scheduled. together w ith phase engineers on both these projects and once current cathodic system integrated with the one of the roads contract and upper parking again the brief includes structures. road design same system which is used for the fuel supply level. The completed building complex is due and traffic control. sewage and stormwater line under the apron. for final handover du~ing the second half of this disposal and reticulation for water supply. The domestic water for the terminal buildings is pumped to tanks situated in the service tower of the main building and in the roof of the office block by two two-stage centrifugal pumps. the operation of which is automatically controlled by float switches in the tanks. Water for fire fighting purposes is taken to specially designed fire hydrants on the apron and on the land side of the main buildings. These hydrants have a calculated flow of 6.8001/min per hydrant unit. Fire hose reels in the buildings and sprinkler systems in the park­ ing garage and in the basements of the main buildings are also fed from the fire main. The freight complex will have similar provisions. Three diesel-operated. single-stage. centri­ fugal pumps are provided in the reservoirpump­ house for boosting the water pressure in the ring main forfire-fighting purposes. Operation of these diesel pumps is controlled by flow switches in the hydrants and sprinkler systems. A central control panel in the main building indicates operation of any of the flow switches and provides manual control of the pumps. Stormwater and sewage drains The stormwater drainage system at the airport discharges under the apron and runway system towards a low lying area to the east of the main runway. Most of the extensive subsurface and surface drainage to the new terminal buildings. the underground parking garage. the new roads and surface car parks. are drained to these out­ lets to avoid cutting through the existing run­ ways. Stormwater runoffs have however Fig. 7 Credits increased considerably with the build-up of View on to apron from public area of Clients: SA Public Works Department surfaced areas at the airport and additional first floor departure concourse. Note steel Architects : Erik Todd, Austin, outlets to the west. through the new provincial cruciform columns supporting roof Sandilands and Partners road system. have been used to assist with the in the background Quantity Surveyors: Quantity disposal of stormwater. Fig. 8 Surveying Consortium Sewage from the terminal buildings and the View of first floor departure concourse. (Photos: Lynda Shave) new hotel on the airport property is conveyed Entrance to the concourse is from the through a twin 230 mm sewer running under motorway on the right and check-in the terminal buildings and out to the north counters are on the left

/ / 17 Finite element e Incremental settlement gauge computations of 0 Hydraulic settlement gauge D Inclinometer ground movements V Lateral spread marker beneath a trial I ~ Slip surface indicator embankment · '!.,, i ·- =,.,-. I ... ·- C.S.4 SA~D =- Brian Simpson DR,+IN AREA This paper won second place in the I =- ':' competition for the 1972 Cooling - C.S. 3 Prize of the British Geotechnical Society. 1c.s. 2 I C.S. 1 ~gcided !Control I ,section !fa ilure Introduction I ---=O c:=-- 1 • In the design of large embankmen~ for roads I and dams. and of structures for which founda­ I tion movements are of critical importance. it is --= / ~ 6 I 6 increasingly necessary to obtain accurate pre­ I / dictions of displacements. For this purpose the -L._ soil mechanics group at Cambridge University has proposed several str11ss-strain models of i --, - soil behaviour, and in the last three years I have developed a computer program which uses these models to predict displacements in soil masses by means of finite element techniques. The program has been used successfully to predict the results of model tests in the labora­ tory, but it was desirable also to test it against full-scale field trials. An opportunity for this arose when data from a trial embankment for the Kings Lynn Bypass were kindly made avail­ able by Mr P. F. Wilkes. Project Engineer to the Norfolk County Council. The project has been described in detail by Wilkes7 • The site V The Kings Lynn Bypass will skirt the town to the south and will consist largely of embank­ ment built on fenland. The typical site chosen r f I I r ' for the trial was about 750m east of the Great Ouse; it had previously been used for a bowl­ ing green. The trial was conducted with the 0 10 20m ------two aims of testing the effectiveness of sand Fig.1 drains and finding the maximum height to Plan of the trial embankment which an embankment could be built rapidly. On the plan of the embankment in Fig. 1. the four instrumented cross-sections are indicated; two of these (Sections 3 and 4) had sand drains and one of the undrained sections (Section 2) / ">. C.S.2 was loaded rapidly to fa ilure. The embankment was heavily instrumented, and only those instruments which will be referred to later are /~---s shown in Fig. 1. The existing road embankment (a) to the south of the trial probably affected the =====~----ropsoi1Soft brown======~~:;;::;:;;::==~== clcy Firm ~y____ _ failure mode of Section 2. luo clo A site investigation was carried out by Messrs Pt Soil Mechanics Ltd. The strata found for Sec­ tion 2 are shown in Fig. 2a. and similar strata were found for the other sections. Wtolhtrtd Kimmoridgt cloy The stress-strain model In the finite element method, a set of constitu­ tive equations is required to relate the stresses 0 Sm 10m and strains of each element so that overall -----j equilibrium and compatibility conditions can ~ be applied. A mathematical model relating ..... "'F =r-, strains to effective stress was developed after (b) studying the findings of a nun,ber of workers at / 1- f "', / ~ '- Cambridge University on the deformation of -· ·, remoulded kaolin. In its main features, how­ ever, the model is consistent witt; the known -- CLAY cj, = 31° c. = 0·85 K.= 0·8 •. :1-7 c, = 0·089 r = 2-1s 2 ·74m characteristics of many soils and uses as its PEAT cj>' = 46° c. = 4·4 K.= Oil t : 6·6 c, = 0·44 r = 9·5 1·22m most significant parameters the angle of inter­ Rough nal friction. 0', the compression index, Cc, and CL AY c. = 0·8s K = Oil C,: 0·090 rigid '*'' =31 ° 0 • . = 1-45 r = 2-15 2·14m the parameter r. {If a normally consolidated boondoriu SANDY c. = 0 ·39 K = 0 ·8 1·83m soil fails in shear at voids ratio e, and mean CLAY '*'' : 34° 0 •. = 0-9 c , = 0-055 r = 1·3 normal stress p 1, then T=e,+ Cc log10p,). The model may be regarded as a further devel­ Fig. 2 opment of the 'Cam-clay' model3. and is inten­ Soil strata and applied loads : ded to be suitable for a wider variety of soils and (a) in the trial (Section 2). soil states. In the Appendix. 'Cam-clay' is briefly (b) as assumed for computational purposes 18 defined and the modifications are listed. at a constant level of 1.25 m below ground level ; this depth was found in the field trial to SETn.EIENT Im) be 1.0 m on average. 0 0 ·2 o-, 0·6 O·& 0 It was assumed that the soil was 99% satur­ LATE RA L ated and. in the undrained case. erratic fluc­ SPREAD tuations in predicted pore pressures between (ml FIELD adjacent elements were smoothed out bet­ 0·6 ;;7·~ u 17· ween increments of load. This process is believed to represent satisfactorily the behav­ iour in the grounds. In the drained and undrained cases. 156 and I ~ .Y · 200 constant strain triangular elements were used respectively. Although these were suffic­ ient to represent the behaviour of the ground at moderate displacements. many more elements 0·2 00f/ would be required to study failure adequately. Results 0 FIELD • End of construction I had access to data from the instruments as 0 2 4 6 8 DEPTH (ml shown in Fig. 1. For Sections 3 and 4. which • 210 days • 700 days FILL HEIGHT had sand dra ins in the trial. displacements at (ml the end of construction (which took about 20 days) and after further periods of 21 O and. Fig. 3 where known. 700 days, will be compared with Fig. 5 Settlement profiles for Sections 3 and 4 the predictions for the undrained and fully Horizontal displacement profiles for (averaged) at 5.75m from the centre line drained conditions. Further settlement after Section 2 at 5.75m from the centre line 700 days is thought to be due mainly to secon­ dary consolidation. For Section 2. which was tested to failure. attention will be concentrated on conditions shortly before failure. DISPLACEMEN T (ml 0 0·1 0·2 0 x-u u--. . 4n H.S. 412 H.S. 413 H.5. 414 Settlements 0 u To give the most useful comparison. the results FIELD\ !COMPUTED IELD / COMPUTED from incremental settlement gauges 301. 302 . •...______u 401 and 402. which were all equidistant from 2 \ I 0-2 D • the centre line (Fig. 1 ). have been averaged; X U ~ ~ I I _,,/',l the standard deviation was found to be about ,,. failure load / _/ 5% of the largest settlement. The settlements. / J U X

O•• measured at the changes of strata. are com­ /; Fail~ a ./ · pared with the predicted values in Fig. 3. ~u u ~ It is seen that both short term and long term II// 0-----0 settlements are successfully predicted. 0·6 D 6 II,/ SETTLEME NT Settlements at ground level were measured by hydraulic settlement gauges. The computed DEPTH 1ml (ml results and those measured for Section 4 are 8 COM'UTED u I.Jncta.,4d shown in Fig. 4. It is seen that the short term D Droint d and longer term (210 days) field measurements are bracketed by the computed settlements. Fig. 4 The effect of the asymmetric boundary condi­ Settlements at ground level tions is clearly shown in the computed results Fig. 6 for Section 4: readings taken from for the drained case. Increase of lateral spread hydraulic settlement gauges 411 -414 as embankment constructed Horizontal movements In Fig. 5 horizontal displacements at 5.75 m from the embankment centre line are shown The computations for two stages of loading shortly before failure. notable that the measured lateral spread was Since the measured soil parameters showed The field measurements. taken from Section 2 close to the computed curve for the drained considerable scatter. it was convenient to ideal­ (Inclinometer 203 - see Fig . 1) which was case in the early stages and moved towards ize the ground conditions to give the four strata loaded rap idly and had no sand dra ins. are the undrained curve in the later stages. for with properties as shown in Fig. 2b. The main compared against predictions for the undrained which the construction rate was higher. parameters required were all derived directly case. It is seen that the agreement is again good. Pore pressures by averaging values given in the site investi­ Fig. 6 shows the increase of measured lateral The computed excess pore pressures show less gation report. Values of K0 and initial voids spread of Section 2 as the embankment was agreement w ith field values than do the dis­ ratio were chosen to correspond to a very lightly built up. Also shown are the computed curves placements. Fig. 7 shows the contours of com­ overconsolidated material. and other para­ for the drained and the undrained cases. It is puted excess pore pressures compared with meters. which have been found to be of minor importances were taken from experience or literature related to similar soils. In the computations the embankment was represented by a vertical load acting on the soil surface. Fig. 2b shows how the load was applied incrementally, being spread uniformly over the whole area of the embankment in the first increment. but w ith later increments gradu­ ally concentrated nearer to the centre line. The computations were designed to model the behaviour of Section 2. and for this reason the ·-.!_ s 12-3 12 • 9.g-9 7f :.=__; •0·3 lateral boundary taken for the soil supporting :10·5 the embankment is closer at one side. repre­ •107 11 ·6· • 2 6 ' 10·3 senting the influence of the existing road 8 ____:.) I embankment mentioned above. / · 59 •141 10 4 Two computations were performed. one repre­ 10 senting fully undrained behaviour (the short term response to rapid loading) and the second Un•t, . head ol watt.r I in metr es representing fully drained behaviour (the res­ I ponse at the end of primary consolidation); Sm 10m the same stress-strain model and parameters Fig. 7 were used for both computations. For the Computed and measured excess pore pressures for Section 2 just before failure drained case. the water table was taken to be 19 piezometer read ings for Section 2. recorded have been presented and the agreement with stresses which is a material constant called the just before failure. The predictions allow for no field measurements has been shown to be critical state stress ratio. (This is related to the drainage. even at the ground level. where there close. value of (?)' for the material when normally was a drainage layer in the trial. and so it is to This type of theoretical work can never reduce consolidated). Deformation at stress ratios be expected that predicted pore pressures near the importance of field tests. but the computa­ higher than this causes dilation and work­ the surface will be high. Predicted pore pres­ tions would cost at commercial rates only a softening. The model used for the computa­ sures at depth are. in general. lower than those small fraction of the cost of the embankment tions described here was similar to that out­ measured. The reason for this is not known. but trial and could be repeated for varying soil con­ lined by Simpson and Wroths and incorporated it is felt that the results are good enough to ditions and soil parameters at neighbouring the following four modifications to Cam-clay. show that the techniques adopted hold con­ sites. (a) The model was expressed in terms approp- siderable promise. Acknowledgements riate to plane strain. In particular the mean Discussion I w ish to thank Mr W. H. Spencer. Director. of the two principal stresses in the plane of The results presented have shown that the Eastern Road Construction Unit, and Mr P. deformation was substituted for the mean programme can be used to predict successfulm Deavin. County Surveyor, Norfolk County normal stress. the two extremes of behaviour - short terly Council, for permission to present this paper. {b} Elastic shear strains were introduced. (undrained) and long term (drained). Vertical I am particularly grateful to Mr P. F. Wilkes for assuming a constant elastic Poisson's settlements could probably be predicted amost having made the relevant field data available, ratio6 • as well by the one-dimensional methods in and to Dr C. P. Wroth, my research supervisor. (c) Although the concept of a flow rule was current use. but the finite element method for much help and encouragement. The com­ maintained. the rule of plastic normality allows good predictions of horizontal move­ putations were carried out on the Titan com­ was disregarded. ments also. To achieve this in a problem involv­ puter which is part of the facilities of the (d) The curve in stress space which was the ing a soft clay taken to large strains requires a Cambridge University Computer Laboratory. yield locus of the Cam-clay model was complicated model of soil behaviour. The Appendix employed in a different way. Deformation results presented here. when considered The stress-strain model and work-hardening accompanied the together with equally accurate predictions for expansion of the locus. but. for changes of laboratory model tests. suggest that the stress­ Cam-clay represents an ideal elastic-plastic stress within the locus. plastic strains strain model used is satisfactory. The main para­ material. limited to axi-symmetric conditions of stress and strain. Fig. shows how the plot of occurred whenever the stress state moved meters required were obtained directly from a 8 stresses is divided into two regions by a yield towards the locus. and the plastic stiffness standard site investigation report. Previous was determined by the distance of the workers have assumed isotropic elastic behav­ locus. Within the yield locus only volumetric elastic strain occurs; it is assumed that there is current stress state inside the locus. iour2 or an elastic stress field 1 • The method used here. however. employs stress and strain no elastic shearing. If the stresses in a small References fields which are entirely compatible. being reg ion of the material change. so that the stress {1) BURLAND. J. B. A method of estimating state crosses the yield surface in the plot of related by the elastic-plastic constitutive laws. the pore pressures and displacements beneath Fig. 8. plastic deformation takes place accom­ embankments on soft. natural clay deposits. The influence of the lateral boundaries selected panied by work-hardening: the yield surface Stress-strain behaviour of soils. Proceedings for the computation requires further investiga­ expands and the amount of expansion deter­ of the Roscoe Memorial Symposium. tion. From an early stage the movement of the 1971, mines the plastic shear strain. The yield locus pp. 505-536. Foulis, 1972. soil follows the pattern which is fully developed is assumed to be a plastic potential and a flow (2) DAVIS, E. H. and POULOS, H. G. The use at failure: it is therefore probable that the lateral rule is derived. The yield surface is shaped so boundaries have little influence. provided that of elastic theory for settlement prediction under that the ratio of shear to volumetric plastic three-dimensional conditions. Geotechnique. they. are outside the limits of the slip surface. strains becomes very large at a ratio of principa Movements much smaller than those beneath 18 (1 ). pp. 67-91, 1968. the fill were both predicted and measured at (3) SCHOFIELD. A. N. and WROTH, C. P. heave and thrust markers outside the toe of Critical state soil mechanics. McGraw-Hill, the embankment: the correlation was poor, 1968. however. DEVIATORIC (4) SIMPSON. B. The use of finite element The rapidly loaded section of the trial embank­ STRESS techniques in soil mechanics with particular ment failed along a narrow zone. This could not reference to deformation in plane strain. Forth­ be modelled by the mesh of finite elements coming thesis. University of Cambridge. 1972. used here. Simpson and Wroth6 describe the (5) SIMPSON. B. and WROTH. C. P. Finite effectiveness of a method of refining the mesh element computations for a model retaining automatically in regions of high strain and so wall in sand. Proceedings of the Fifth European modelling the formation of a narrow slip zone. Conference on Soil Mechanics and Foundation Secondary consolidation will be considerable Engineering. pp. 85-93, Madrid, 1972. in the organic clays and is not predicted by the (6) WROTH. C. P. Some aspects of the elastic present program. However. other workers in behaviour of over-consolidated clay. Proceed­ the field of finite elements have successfully ings of the Roscoe Memorial Symposium. pp. modelled problems involving creep behaviour8 • 347-361. Foulis. 1972. MEAN Conclusions "'--'--'-~..___.___.~..,___._~+--'---"-~NDRMAL (7) WILKES. P. F. An induced failure at a trial The finite element method has the potential to STRESS embankment at Kings Lynn. Norfolk, England provide the link between academic theories of locus Proceedings of the Specialty Conference on stress-strain behaviour and the field predic­ Performance of Earth and Earth-supported tions required by practising engineers. In this Fig. 8 Structures, pp. 29-64. ASCE. 1972. paper results produced using a complicated The yield locus as used in the (8) ZIENKIEWICZ, 0. C. The finite element model of soil behaviour based on parameters stress-strain model method in structural and continuum mechanics derived from a commercial site investigation (Second edition). McGraw-Hill, 1971.

20 700.000 homes built using large panel systems provided for doors and windows with the Design and in Europe that yea r. frames frequently cast in. Why conrete panels? The greatest difference between the systems construction occurs in the production of floor panels. It is interesting to note that of the 22 successful These may be cored or solid. prestressed, bids under the Break-through programme. (see innovations: post-tensioned or normally reinforced. The Appendix). nine systems propose the use of method will often depend on the background concrete as the main structural material and, systems utilizing of the sponsor. of these. seven a re load-bearing panel systems. panel components In the light of European experience this was Specialists in precast plank w ill tend to design not unexpected. around their product which provides pre­ stressed panels of up to 1 2 m span in 0.6 m or In the first place, concrete itself is a relatively 1 .2 m widths. Considerations of differential Jim Morrish cheap building material. it is durable. lends deflections. horizontal joints and surface itself to a variety of architectural treatments finish have to be carefully taken into account. and has read ily available sources of raw This paper was given at the Conference on material which, with a minimal amount of Others utilize horizontal forms. carefully Industrialized Building Processes. held at pre-treatment. can be incorporated in the engineered to provide normally reinforced the College of Engineering. West Virginia building. units of high dimensional accuracy. The University, Morgamown. West Virginia. USA. bottom surface produces a smooth mould on 26 May. 1972. Given sufficient repetition. substantial savings face. the top is trowelled and covered by a in cost and improvements in quality can be suitable finish. The trowelling can be by hand achieved by precasting components. in either or mechanical and the applied finish may be Introduction central or on-site plants. The most usual incorporated at the time of manufacture. By Man's basic requirements for shelter are a roof. demonstration of this is in the large scale placing the moulds on a production line. they walls. and preferably a floor. He has provided production of precast flooring of various can be moved to operational stations. includ­ these in a variety of ways according to the proprietary forms. ing those of concreting and curing. which climate. the materials available and the area in Traditionally, multi-storey constru ction evolves provides a continuous cycle of operations. which he lives. As his skill in use of tools has around the erection of a structural skeleton, The heavy capitalization involved in this type improved so has his degree of sophistication the bones of which are beams and columns. of plant demands the maximum amount of in the assembly of the materials. which in its either in steel or concrete. Floors are added repetition of a few number of variations in turn has led to an increase in size and amenity and this forms the frame to which space slab types. of the buildings that he has constructed. dividers. external fai;:ade treatment and Floor slabs can also be cast in vertical batteries The era of industrialization with its emphasis services are added to suit the particular needs in a method similar to the production of walls. on the use of machines and mass production of the client or his architect. The advantage of obtaining two smooth techniques to make consumer goods available Several systems have been developed based surfaces is an obvious one. The equipment to all but the very poor. has somehow not on a continuation of this approach and. in occupies less floor space and the same labour resolved the problem of housing in the ·urban crews can produce both floors and walls. environments that it has created. situations demanding maximum degrees of flexibility in planning. they are beginning The size of slabs can be varied within the The wider spectrum of the problems involved to demonstrate their worth. There are certain confines of the battery cells. Careful quality have been discussed in depth by others at design and construction pitfalls. notably in control is essential and to maintain economic this conference and possible solutions have the areas of connections and tolerances. utilization of the equipment requires produc­ been argued. On the assumption that the tion planning of a high calibre. socio-economic problems have been resolved Within the apartment sector the extreme flexibility is an unnecessary luxury and other. There are other less common techniques we. the designers. are still given the same which have now passed the experimental basic criteria. i.e. using today's materials and more demanding. criteria must be met. In addition to structural strength, particularly in stages. One produces panels by pouring a today's tools we must provide the shelter wet concrete mix into a mould and squeezing needed today. high rise buildings. there is the need for minimum sound transference. for adequate the excess water out under high pressure. It is It is my brief to discuss the use of one of those fire res istance between dwelling units, for possible to produce four panels per hour from materials. in the various large panel systems low maintenance costs and. if the national one mould using this method. Unless a that have been utilized so widely in the problem is to be met. for speed of construction. completely standardized product is desired, construction of housing and other associated the rate of production could be an embarrass­ buildings. Systems incorporating the use of large load­ ment. Further development work should bearing concrete panels supporting concrete History resolve this anomaly. floors to which they are sensibly jointed. will The use of concrete as a building material has fulfil all of these requ irements and at the same All production methods allow for the formation really only gained recognition since the turn time make the least inroads into the already of holes and sleeves to accommodate of the century. It comes as a surprise. therefore. scarce skilled building trades. In erecting the plumbing and mechanical services. to realize that as early as 1905. in Liverpool. structure not only are the bones provided but The architectural cladding can range from a man called Brodie was casting room size also a substantial amount of the flesh, which the rather brutal plain concrete panels with wall. floor and ceiling panels in a central will eliminate follow-up trades. rectangular windows offering the only rel ief. depot and hauling them by steam tractor to to very heavily profiled units using multi­ Production methods be erected on site. A three-storey apartment coloured aggregates and cements or mosaic building still exists. From the ·20s through the Despite the differing methods of production and ceramic finishes. The former is very cheap '40s various attempts were made to introduce and assembly, all the systems can be but has created a public reaction against 'low techniques which were not too dissimilar recognized by the types of component cost precast housing·. The other extreme can from those used today. but although numbers produced. be visually more satisfying but is generally of successful buildings were completed both Load-bearing walls are normally 150 or achieved with some sacrifice of the internal here and in Europe, the large scale develop­ 180 mm th ick. dimensions which will provide amenities because of its greater cost. ment of these ideas did not take place. the necessary sound insulation between Curtain walling. plastics. brickwork and other It was not until the '50s that circumstances dwellings and at the same time provide proprietary panels have all been used in an in Europe created a favourable climate for the structural strength for buildings of approxi­ effort to achieve variety. large scale usage of these systems. These mately 20 storeys without the provision of circumstances are all well known. The special reinforcement. They are usually cast Storage and transportation aftermath of two world wars created a vertically in multicell steel batteries. This It is tempting to think only of production and tremendous and urgent demand to replace provides a smooth face to both sides of the erection processes. since these are the areas houses destroyed and slums that would no wall which then requires the minimum amount where the most dramatic demonstrations of longer be tolerated by the emerging societies. of preparation to receive a painted or papered technology are to be seen. Unfortunately. There was an acute shortage of traditional finish. Some systems manufacture to standard there have been a large number of builders building materials and skilled labour was at modular lengths. usually 1.2 m or 2.4 m; lured by the temptation to dismiss half their a premium. Builders became more receptive others attempt to provide room size units labour force and produce apartments at an to new plant-orientated techniques and sup­ based on a more flexible module. astonishing rate merely by purchasing Brand-X pliers were able to revive the dormant ideas and Most producers incorporate electrical conduit equipment. to suggest new ones. In France and Eastern with switch and socket outlets; this may be Without the superior management skills which Europe the governments were able to ensure pre-wired but it is not usual. Other plumbing are the key to the exercise. the misuse of the a continuous programme of work which and mechanical installations can be cast into plant can lead to inevitable bankruptcy. One enabled development to take place with an the wall provided that they can be accom­ mistake per week made in the traditional assured return on the heavy capital investment modated in the thickness. More often holes manner can be more easily discovered and required. Great Britain was relatively late in and chases are provided to receive sub­ rectified than the same mistake repeated in the field but in 1968 produced 21.000 of the assemblies at a later date. Openings are also 50 panels before it is realized on site. The 21 higher the production rate the more vulnerable mechanically by welded or bolted devices or those already fixed. The requirements of some is the system. by means of ·wet' reinforced or post-tensioned codes can also inhibit prefabrication. Careful attention must be paid to the balance concrete techniques. Accurate precasting will provide holes for between production and assembly. A plant The mechanical solutions call for a high pre-planned independent arrangements which producing 40 dwellings per week w ill soon degree of accuracy in casting and assembly ; can be fixed efficiently. To allow for flexibility be forced to curtail production if the erection they also involve the use of skilled tradesmen a combination of holes can be provided and rate drops to 35 dwellings. There must be to ensure a sound connection. Provision has those not used filled in afterwards. adequate storage space to allow for unpredict­ to be made for temporary stability in order The manufacture and use of complete kitchen able weather or labour difficulties. This storage that valuable crane time is not absorbed and bathroom assembl ies in off-site factories must be planned to avoid double handling of during erection. is not a technical problem. Unless a large units. otherwise the cranes will spend more Most Western European systems tend to favour market is assured, however. it is still at this time searching and sorting than they will structural joints using cast-in -place concrete time cheaper to use rationalized traditional loading panels. The stacking frames must be and dry packed mortars. The use and disposal methods. Safeguards must also be provided well designed to avoid the consequences.of of reinforcement in the joints depends on the to protect these fin ished products during accidental damage when moving units method of manufacture and the sequence of construction. weighing 10 tons or more. erection. These operations are more tolerant Heating and ventilating systems are normally There are always certain critical panels which of dimensional inaccuracies. can be carried fall outside of the ma in production run. In the from trad itional sources. Once aga in they are out independently of the placing of units and supplied vertically. unless individual units are event that these are not available when require no particular high skill. Normal cold requ ired then erection must cease despite an used. and distributed horizontally within the weather precautions have to be adopted dwelling. A convenient location is next to the abundance of general stock. Although these during w inter but the early en closure of the may seem to be elementary points. lack of fa i;ade panels which can be profiled to bu ilding space helps to minimize exposure accommodate pipes or fans. Some wall or attention to them can soon create a situation to the elements. where the increased productive capacity will fl oor panels do have heating elements cast in. only serve to multiply the problems. Weatherproofing can once again be classified Elevator shaft walls incorporate guides and by family type. From the designers' viewpoint inserts which allow for completely pre­ It is in this field that the training of the it is tempting to call for pla in-ended units and assembled cars and motors to be installed professional can be deployed to advantage, joints caulked w ith mastic. The quality of prior to putting the roof on . This single factor but he must be aware of the complete process mastics has improved enormously over the can reduce the completion time of a 20-storey in order that his designs can be economically years and. provided that manufacturing and bu ilding by three months. produced. erection tolerances are ma intained w ith high Although electrical distribution is provided Erection quality workmanship in their application. a through cast-in conduit. this technique is not Erection is usually carried out by teams of sound joint w ill ensue. It is rarely possible to w ithout problems. A series of walls produced eight to 10 men serving a crane. The type and execute this work as erection proceeds. As an from the same mould may have a number of capacity of crane is a function of the system alternative, preformed compressible strips electrical variations which are not always philosophy. Smaller units can be handled by may be inserted into grooves cast in the apparent to the man producing or placing the light mobile cranes which can collect their panels. but variation in joint widths can affect panels. Horizontal distribution is usually own panels from loaded trailers. Large room their efficiency. through pre-formed baseboards incorporating size panels require less number of lifts per Open-drained joints are most often used for a raceways for electricity. telephone and floor but need heavier cranes w ith sensitive variety of reasons. They can accommodate television cables. slow speed controls to assist the crews in variation in joint w idth and thermal movement. Economics and disciplines locating the panels. Since they are made at the time of erection. The main aim of this presentation has been In Europe these requirements have resulted their formation and inspection can take place to describe what constitutes a large panel in the design and manufacture of special ist from inside the bu ilding. The materials used system. how it functions. and how it relates families of tower and portal cranes which are not dependent on age or weathering to the other subsystems which form the provide the facilities needed by a system characteristics and consequently the joint is finished building. This methodology is fine sponsor. On ce aga in the designer must be ma intenance free. It does requ ire good provided that it is not just considered to be an aware of the capabilities of the equ ipment. detailing. however. particularly at the inter­ section of vertical and horizontal joints and exercise in technical virtuosity. It must be Where other prepackaged subsystems are can create manufacturing difficulties for able to demonstrate that these buildings can employed it is usual to place them in position elaborately profiled architectural panels. It either be obtained more quickly or more prior to the next level of floor slabs being has been thoroughly tested in exposed coastal cheaply or preferably both. In Europe this has erected. conditions in Norway and Scotland and been so. particularly in the medium to high Before the structural joints are completed the rarely gives trouble. rise field. In the United States it is probably wall panels are temporarily braced whilst they still too early to draw any valid conclusions. are levelled and plumbed. The exact method Thermal insulation Traditional costs themselves are tremendously and equipment to be used should be decided Where concrete is employed as the cladding variable and can range from as low as $1 3/ft2 during the design phase. material. thermal insulation is normally to S34/ft2 in the New York area. Such The planning of the erection sequence should achieved through the use of sandwich panels. predictions as we have been able to make always consider the follow-up operations that Difficulues can arise at the Joint between suggest that. with a properly planned and are necessary to complete the finished panels and around openings where there may controlled operation. savings of the order of building. Merely producing a concrete be a discontinuity in the insulation giving rise 7% can readily be achieved but that. with the structure at an accelerated rate is only to thermal bridges. The relative impermeability present generation of systems. it is doubtful addressing something of the order of 35% of of concrete surfaces can lead to problems of if figures of more than 10 to 11 % are going to the total process. The building must be made condensation under combinations of low be exceeded even in the most efficient weathertight as close behind the erection temperature and high humidity. The insulation conditions. There are. however. unseen level as possible in order that the finishing should thus be considered in conjunction savings to be realized in early completions on trades can perform. These trades and sub­ with the heating and ventilating systems. site. Being able to hand over a building with a 30% time saving, for example. can lower the systems must themselves be related to the Electrical and mechanical services total process. construction loan interest by 3%. At the same It has not yet been found practical to achieve time. income from the building is realized at .Jointing the ideal situation in which all the sub-systems an earlier date. In areas of urban renewal the Whenever system builders. or their designers. can be pre-assembled. placed in position and cost advantages which accrue from time assemble. the discussion will inevitably come merely connected up. Even where the saving are possibly not as important as around to one of two topics. components are ava ilable. their final location providing new homes for those in need . 1 How do you tie the panels together? can interfere with the temporary propping necessary until the joints are structurally To achieve these savings there are some basic 2 How do you keep the weather out? sound. requirements. the first of which must be good The first of these has tended to attract the design. There is no such thing as an infinitely greatest publicity since the accident at Ronan An economic storey height will not allow for flexible system and the designer must Point. and quite rightly structural safety is of long horizontal ducts with complicated recognize the disciplines and constraints with paramount importance. Unfortunately. there intersections. The tendency is to provide a which he has to work. Having recognized has been an infinitely higher failure rate in the series of vertical service cores which contain them, they need not necessarily be considered second field due to lack of attention to small utilities for dwellings in the immediate vicinity. to be unduly restrictive. The worst possible details at the junction of units. Prefabricated plumbing assembl ies are used exercise is to take an existing design and try The basic principles of structural connections and can work. but care is needed in the to convert it to a system solution. are now fairly well established. The details of consideration of tolerances and movement. Having realized a good design there must be implementation constitute another major area Since pipe connections are normally located a continuing market. The capital cost of setting of difference between the systems. The in relatively restricted areas. it is often difficult up the equipment for even the most unsophis­ 22 essential tying together can be achieved to join one unwieldy set of components to ticated system is as high as $1 m and can go up to the $5 m mark. A continuous demand The information that they can supply is development skills. This aroused the interest over a number of years can be very much needed at the very outset in order that moulds of the whole of American industry and most more valuable than one large order requiring can be set up. equipment ordered and of the European system sponsors. heavy capitalization in equipment with no production schedules arranged. This must 22 prototype sites across the USA were to be follow-up activities to maintain the plant mean the abandonment of the concept of the developed and the 10 most successful systems utilization. Some factories can exist on 300 or isolated professional working in his own were to be given top priority to the 'set-aside' 400 units a year. others need 1.000-2.000. sphere with little concern for the problems of funds provided by the Government over the Since the material content is the same. it is others engaged in the building process. The next 1 0 years. The target was 26 million clear that the major economies are to be made leadership of this new design team will largely homes. in the more efficient use of labour and in be governed by the organization sponsoring This provided the incentive for Wates Ltd. of creating opportunities for relatively unskilled the system. but can be architect. engineer. London to form a joint venture with the Rouse labour. This can only be successful with the contractor. or client. The omission of any of Company of Maryland (the 6th largest cooperation of the unions. It is not only a the participants at the start can only lead to an mortgage bankers in the USA). Arups were question of basic wage levels but also of num­ out-of-balance system. If the concept of invited to provide engineering support in bers of persons employed per operation. If a industrialized building only serves to get us North America. normal erection crew of eight to 1 0 men has all to operate in our own jobs in a more The Rouse-Wates submission was amongst to be increased to 20 or more because of de­ efficient way. then this alone would justify the initial 22 selected and successfully marcation disputes and trade practices, the its introduction. completed a scheme of 240 apartments in system is defeated. Appendix : St. Louis. They were also amongst the three It is also very important to have good manage­ Operation Breakthrough or fou r final su rvivors of the va rious political. ment at all levels. It is not enough to have top Operation Breakthrough was the name given financial and bureaucratic battles that elimina­ level people in production and construction by the Department of Housing and Urban ted some 400 of the original hopeful alone. A key to any successful system is the Development to an ambitious programme contenders. design which it must meet. The reason why launched with the object of linking the space The uncompleted final phase of Operation large panel systems can be so competitive is age technology to the solution of the acute Breakthrough. the 'set-aside' funds. was because the problems have been thought out housing and urban renewal problems of the abandoned together with all Federally assisted beforeha nd. This requires a complete collab­ USA. housing programmes in January 1973 and an oration on the part of the architect. the An international competition was created in 18 month moratorium on these programmes engineer. an d al l the va rious mechanical and la te 1969 which invited 'innovative· proposals has been ordered by the new Nixon electrical consultants and subcontractors. based on planning. technical. financial and administration.

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