THE ARUP JOURNAL

SEPTEMBER 1972 Vol.7 No. 3 September 1972 Contents Appendix 1 - Application checklist (ii) The location, i.e. whether at ground level, materials (study mixtures of metals due to Published by Ove Arup Partnership 1 Select as first choice the best possible on or within a building. other equipment). THEARUP 13 Fitzroy Street. London. W1 P 6BQ position, checking for: (iii) A guide to surrounding environment, When the tower is to be installed in the open, (a) Effect on tower e.g. built-up areas, woodland, harbour, etc., the enquiry should state whether ancillary items such as immersion heaters, ball valves, Editor: Peter Hoggett Free access for entering air, ample perforation which may affect performance or selection of Art Editor: Desmond Wyeth FSIA Recirculation danger (L< 10H), need fordecks materials. Adjacent railways, process effluxes, strainers, fan guards, cover, thermostats and JOURNAL Editorial Assistant: David Brown Prevailing wind, orientation of tower batteries and industrial chimneys should be mentioned. motor starters are to be- included in the quotation. The Berry Lane Viaduct, 2 Air contamination ; other plant items, effluxes, 3 Limitations by J. Nissen filters Are there any restrictions in height, plan area, 5 Services Uplift in air wet bulb or access for erection which may affect the The enquiry should state the volts, phase, The Evry 1 Competition, 6 Spoiling of fan performance due to position type of tower offered ? Is there a preference cycles of the electricity supply, and should, if possible, give the source of the make-up by M. Barclay of tower in its surroundings for a particular type, e.g. induced draught (low plan area), forced draught (limited air access), water if this is other than town mains supply, The need for fire precautions e.g. artesian well. lake, river. Mass housing - 8 cross draught (height limitation) should be flexibility with standardization, (b) Effect of tower stated. Bibliography by B. Seymour Condensation of moist air discharge; cones Specify also: and bonnets (1) GURNEY, J. D.andCOTTER, I.A. Cooling Limitations due to noise (adjacent residential towers. McLaren & Sons Ltd., 1966. Now A study of a large landslide 12 Downwind vapour nuisance areas at each side or below) available from Applied Science Publishers Ltd. at Heme Bay, Kent, Windage and carryover nuisance Limitations on carryover due. for instance, to by E. Bromhead Noise from fans and water; silencers, part- (2) INSTITUTION OF HEATING AND windows adjacent to discharge VENTILATING ENGINEERS. IHVE Guide speed motors, anti-splash decks, anti-vibration Tubular steel microwave 15 Limitations in working weight due to structural 1965. Section J 5c. IHVE Guide Book, insulation towers for Nigeria, considerations for a roof-mounted tower Volume B. 1970. by M. Shears Weight of tower and water Restricted access for air inlets, and dangers (3) GOLDBERG. N. Control of noise of Dangers from accidental leakage of recirculation. cooling towers. Air Conditioning, Heating and Planning to avoid cooling 19 Appearance and visual suitability. Ventilating. 60 (6), pp. 58-61. 1 963. tower misapplication problems 4 Construction (4) JONES. R. S. Misapplication and incor• by D. Gurney 2 Evaluate any problems and compare alter• The enquiry should state: native locations. rect location of cooling towers. A paper read Whether the casing is to be of before the Cooling Tower Institute. 16-18 3 Examine alternative types, arrangements (a) manufacturer's supply June. 1969. and finishes of tower. (b) builder's work supply Front cover: The Berry Lane Viaduct. (Photo: David Faggetter) (5) KUNESCH, A. M. Relative merits of 4 Provide maximum useful information to Whether the basin is to be of combining natural and mechanical draft Back Cover: Computer drawing of Nigerian radio tower potential suppliers - see checklist for (a) manufacturer's supply cooling towers. A paper read before the specification to suppliers. (b) builder's work supply Cooling Water Association in London on 25 February, 1972 tunnel would have had to be artificially lit attractive than others. Berry Lane passes Appendix 2 — Checklist for specification If (a) in either case, a statement of materials (6) EVALUATED weather data for cooling The Berry Lane 24 hours a day. through narrow tunnels on both sides of the to suppliers should be requested, or specified, in the equipment design. Head Wrightson Processes Our main task was easy to formulate: we site so that only light traffic could pass this 1 Performance - specify: enquiry, as should a description of ancillary fittings such as drains, purge connection, Ltd., London, 1963. Viaduct should design a structure which would not way. The main access should therefore be (i) The water flow rate from the north along the cutting for the future make-up valve, etc. act as a barrier and which would preserve the (ii) The inlet and outlet water temperatures Acknowledgements character of the woods as much as possible. road where it is wide to provide for sliproads. If (b), the enquiry should specify cover for Jorgen Nissen (iii) As a check, the heat to be removed The author is grateful for very real help and It was more difficult to see how this could be This cutting will, of course, not be available supply of all necessary drawings to enable the encouragement from friends and colleagues The Berry Lane Viaduct will carry the London done. A 35 m wide slab suspended some 1 8 m at the beginning of the contract and the (iv) The design ambient wet bulb temperature contractor to construct the casing and/or who have offered advice and guidance, North Orbital Trunk Road over a deep valley above ground is an imposing feature which foundations will, therefore, most likely have (v) Altitude of site basin, including the necessary baffles, filters quoted examples and made pictorial material to be constructed from Berry Lane. Fortunately, in Chorleywood. A small country road called cannot be hidden away, but in this case the 2 Location - give: and drains to trap and remove sludge. available: among these are A. M. Kunesch, they can be made as simple footings as we Berry Lane runs along the bottom of the valley woods seemed to help us. Inside the woods (i) The area or town in which the site is Preference for any material, e.g. type of E. LeMay, J. R. Neller, D. P. Rayfield, K. Rogers found firm chalk below a very thin layer of and the Metropolitan railway runs on the there are no long views along the valley; the located packing, should be stated. Restrictions in and G. Slaughter. south slope. The valley is full of trees and trees stand in the way, and the ground is alluvium over most of the area. very pleasant and much used by walkers. It is mostly in the shade of the trees. The trees are The structure should also be suited for a residential area and private houses lie in the same height as the viaduct and we felt construction over Berry Lane and. more the woods. that we might soften the impact of the important, the railway. This is very busy as it carries the Metropolitan underground trains The North Orbital Road is being designed by structure if we could design a light and as well as trains for British Rail. Work over the the Department of the Environment, but in unobtrusive support structure of the same April 1 971 we were asked to prepare a design scale as the tree trunks. We would, so to for the viaduct. It was only natural that our speak, try to keep the feel of the wood under clients should stress the importance of the the bridge. To succeed in this, it would be environmental aspects in their brief as these very important that the woods should be were the raison d'etre for the structure. An disturbed as little as possible during construc• Fig 1 below tion and that their natural character could embankment had earlier been considered ; it In designing this bridge, we were determined easily be restored in the areas that were would have been some 18m high and around to preserve the woods through which it disturbed, so that a scar would not be left for 100 m wide at the bottom and would com• passes, as much as possible. From this long. This limited the construction methods pletely have destroyed the woods. It would consideration followed ideas for a construc• that we could consider. also have severed the valley into two separate tion method and appearance and these Access to the site is restricted and some parts which would have been connected only principles resulted in the proposed tabletop construction methods are therefore more by a 100m long tunnel for Berry Lane. This structure. (Photo: McMasters-Christie).

Printed in England by Thompson & Tompkins Ltd. Droplets of moisture can be tossed from the rails can only be carried out at night and then Huntonbr d g* tops of high discharge velocity towers even only for three hours at a time and there are Ml when eliminators are fitted. The combination restrictions on the methods of construction that the railway authorities will allow. of concentrated impurities in the water and Strati sunshine will mark the paint finishes on Having identified these main considerations Latimw motorcars and plant. Unless the air discharge we were soon able to establish some general velocity is low, and very effective eliminators principles. It seemed right that a simple are fitted, towers should not be located close repetitive structure should be used ; we could see no reason to single out either Berry Lane to car parks and roadways used by the LaTimar Sta WATFORD general public. or the railway and make larger spans over them and we found in our cost estimates that : (d) Fan and water noise the economic range of spans in any case is ClKr lay weed o0(S This subject and its problems and solutions, larger than both these spans. The conditions urr.moi 1 3 Ml are dealt with in some detail in other texts , . for prefabrication are obviously favourable Cro.lay WortWd It is sufficient here to emphasize the highly and we thought it would be useful to use a O.h.y BUSHEY emotional response evoked by unacceptable split structure with separate decks for each HTl Or

noise levels and to make the following carriageway. This should give some advan• BERRY LANE VIADUCT ICKMANSWORTH Fig. 6 reminders: Fig. 9 tages in construction but, more important, we

L <10H increases recirculation Single entry crossflow could make a gap in the wide slab which Moor Para (i) Running a fan continuously at part-speed would otherwise blot out the sky over the Mapl at night is more acceptable than cycling it on f whole width of the road. This, we hoped, C and off. would help the vegetation under the bridge Chalfont Common (ii) Quiet cooling tower performance can be in establishing itself again as some light and rain would pass through the gap. o o o o o achieved using slow-speed or quiet running North*, tod o o 0 o o centrifugal fans and motors if the supplier At this stage we prepared sketch designs of knows of the problem at planning stage. Also, some structures which all fulfilled the require• Horoli .id -i 'on! HMtfflOM L both inlet and outlet silencers are available as ments mentioned so far. They range from St Mor standard accessories on some makes of tower. continuous girders to tabletop structures with precast beams suspended between in situ 0 (iii) Fan cooled motors are more than tabletops. We considered different cross- ordinarily noisy and should not be used. sections and materials and compared the 6ar rare* (iv) Tower water noise is real, but can be schemes on their functional, technical, r c ; i North Harrow modified by use of anti-splash decks in the economic and aesthetic merits. In the end we o o o o o surface of the water basin. This should be at chose a tabletop structure. This structure the operating water level which will be below compared well with the rest on all counts o o 0 o o the level of the surface when the tower is not and we thought it was superior in one Fig 2 Fig 3 below in use. respect; each tabletop was supported by four The whole contract covers the North Orbital The mam access should be from the north very slender columns which could be made Road between Hunton Bridge and Maple along the cutting for the future road where it (v) Towers should not be mounted in noise- nearly as thin as the trees that surround them. Cross. is wide to provide for sliproads. sensitive courtyards since reflection increases Other structures were supported by two the noise level by up to 1 5db. columns which were necessarily much Fig. 10 thicker. We compared these two column Prevailing Wind (vi) Fan/motor/gearbox noise can be trans• Crossflow induced draft mitted through the structure of the plant and types in simple models and found the thicker building, and the usual precautions taken for columns much more conspicuous although o o o o o moving plant items apply also to cooling only half the number was used. As mentioned 11 o o o o o towers. Ask, what is situated below the before, the trees tend to hide the supports if The construction of the tabletop structure is cooling tower? ! t ! they are slender enough. We also found that well suited to this site. The smaller part of the the relationship between the four columns is structure is cast in situ; it is reinforced only, \2 (e) Weight of tower and water PT7 important; they should be close enough not prestressed, and we have made the It is not always recognized that the operating together to read as a group and not just appear members bulky so that the concrete can be I Fig. 7 1f t I V Orientation of multiple tower weight of a cooling tower is high, that the as a forest, but they should not be so close easily placed. Each tabletop is stable at all banks, D to be < L quantity of water held within the packing and • 1 J that the light and diffuse character is lost. stages during its construction and it provides contained within the storage basin of even a Tabletop structures form a clear and simple a platform from which to place the precast MS *^ packaged tower may well equal the weight of f structural system and this perhaps adds to beams. These can be brought in from one end. the tower itself. Suffice to say that the their appearance. It is easy to see how the There are no bearings or complicated joints f ii^.r™ foundations or structure beneath the tower structure carries its load and how it is within the in situ work to slow up construction must be capable of carrying the weight of constructed. All the precast spans rest simply and scaffolding can easily be erected on top VIADUCT tower plus water! supported on the tabletops and each tabletop of the footings. We thought at first that it RESTRICTED ACCESS is in itself a stable structure which carries all would be a good idea to save some of the • (f) Accidental leakage loads that act on it, including bending and scaffolding and we studied a scheme for Once again, ask, what is underneath the horizontal loads, to its foundation. We chose casting the tabletops at ground level and ,J-4 .: tower ? to make the tabletops comparatively short then jacking them up on the columns. This V ICI'H The design of the piping circuit between the 1 and to support the suspended spans on produced no savings and it introduced an hinges at both ends in order to limit the awkward joint to be made when the tabletop cooling tower and the plant which it serves RESTRICTED ACCESS should be studied to determine the quantity bending that has to be carried to the had reached the top, so we gave up the idea. of water which will drain down into the tower foundations. Having taken the fundamental decisions about basin when the pumps stop. Can the basin Fig. 11 the structural system and how to build the accept this water without waste through Forced draft overflowing ? Draining of the heat exchangers in the plant should not be permitted since other operating difficulties arise as a result. Fire precautions Extent.on (g) Appearance Con* It is not always recognized that a cooling The engineer, as well as the architect, should tower is a very real fire risk. There are many be concerned about the appearance of the cases of destruction during the plant construc• tower, both when new, and also after some tion phase, from welding sparks or due to a years of operation with minimum maintenance. casually dropped match or cigarette. A timber Perforate Quite often the architect does not appreciate Screen tower which has dried out during a period of Wall how large a cooling tower can be, nor that maintenance is easily set alight - and the there is such a wide choice of types, arrange• natural draft effect quickly fans the flames. ments and finishes. There is full scope at the In and on buildings, sprinkling or drenching planning stage, but very little by the time the engineer is finalizing the details. of the outer casings may be advisable. In general, it is common sense not to allow a There are many examples of towers totally timber packing to dry out completely. unsuitable for their surroundings, which While there is still no standard for fire become an eyesore and a sad monument to precautions in respect of cooling towers in the Fig. 8 the lack of care, understanding and interest United Kingdom, the National Fire Protection Towers installed of the building designers and site planners. Association in the USA publishes NFPA behind screen walls Nobody's baby grows up with a very sore Standard No. 214 which is a useful basis for thumb! study of underlying principles. It is suggested that any space and cost be used in circuits containing copper con• penalties, avoided by not taking precautionary denser tubes. measures against recirculation, will be more The general solutions and precautions to be ^ I 1 than offset by the increased costs and taken include: C3 o embarrassment caused by subsequent lack of H 21 \ thermal performance and remedial action (i) A careful study of the proposed location in relation to both the plant or building which ,:i \ \ which will have to be taken. the tower is to serve, and also a survey of i (c) Uplift in air wet bulb temperature possible sources of trouble in the surrounding UJ 9 sl The dependence of the water cooling tower area. upon the wet bulb temperature of the entering O O air is well-known. What is not so often (ii) Consideration of the use of air inlet filters appreciated is the severe penalty on thermal (these must be regularly cleaned or water will q i performance which results from incorrect be held up within the tower). In heavily air - selection of this leading design parameter in contaminated areas, such as steel works, the • I a 2 : terms of the effects of surrounding features, use of bypass water filters may be advisable. 1 1 • M i \ 1 6 M.I 1 Li both natural and man-made. Other texts , (iii) In areas of heavy environmental pollution, 7 should be studied for detailed information, consideration of the use of closed circuit ; since space permits only brief comment here. i cooling water circuits using either air blast Forced draft Half an induced draft 1 :: i Situations in which the wet bulb will be ! (fin fan) coolers with subsidiary sprays under counterflow crossflow i M l 07 increased include the following : elevated ambient air temperatures, or alterna• • • 5 tively closed circuit coils within a cooling (i) Recirculation: Kunesch in his recent Fig. 4 tower concept, making the necessary detailed paper quotes numerical examples which studies. o indicate the seriousness of this problem. z (iv) Planning for effective water treatment items is a near certainty. The results can vary o (ii) Air discharge grilles from building air O and regular blowdown, as necessary. The from distasteful nuisance to actual damage, ! o o conditioning, process steam discharges and advice of a recognized water treatment including : effluxes from other cooling towers, from hotel specialist should be obtained. Mixtures of (i) Staining of buildings, including salt o bathrooms, laundries and so on, can adversely metals in construction should be carefully 1 deposition and biological growths 9 a . .H20 O affect cooling tower thermal performance by studied and incompatible mixtures avoided - no elevating the entering wet bulb temperature. water treatment is not a panacea in such cases. (ii) Corrosion of metal surfaces (iii) Etching of glazing. (iii) Close presence of dense vegetation, (e) Reduction in fan performance SITE PLAN particularly if the tower is surrounded by damp The effect of altitude on air pressure must be Use of lower water loadings (larger tower plan natural growths. taken into account in the determination of fan area and greater vapour dispersal) use of performance. extended fan cones to carry the nuisance past Certain advantageous situations can arise in the surfaces and also tilting the fans away from which the wet bulb is reduced : •j.'.r 5 Restriction of air inlets, dirty air inlet louvres critical areas, have all proved effective. or filters, dirty or maladjusted packing and (i) Wet bulb reduces with altitude : the correc• (b) Downwind vapour drift 1 6 water distribution, blocked or dirty eliminator tion suggested for the British Isles ' is about Even when condensation on critical surfaces 0.5°C per 100 m of elevation. sections, and restriction of air discharge, n all adversely affect the cooling tower is avoided, the warm moist air stream will (ii) The presence, upwind, of large stretches performance. condense, at periods of critical dewpoint, into of water actually can have the effect of a cloud of vapour which can persist for All the relevant factors previously discussed lowering the incident wet bulb. considerable distances downwind. In really should be taken into account in order to difficult situations, such as near aircraft run• If the cooling tower supplier .is aware of the reduce these effects - in particular the ways, gas burners have been installed within sources of possible influence on wet bulb proposed location should be studied for the fan discharge stack - but the cost of their temperature in the neighbourhood of the site, secondary obstructions to air flow such as use is very high. Fine nylon mesh screens arrangements can be made to take these into beams, cills, parapets, and items of equipment SOFFIT PLAN have proved effective in one instance known account in the design and selection of the which may not be installed according to plan. to the author, by causing a percentage of the tower. In particular, structural members such as moisture to condense above the tower. beams can create serious vibration problems (d) Contamination of air and water by disturbing the flow of air over the leading (c) Windage and carryover Tower performance can be adversely affected edges of the fan blades. At times of high wind, water may be blown by entrainment of foreign matter of various out of the bottom of towers unless crosswind 12 5 II10 S2 0 3?0 31'I) !;•() .120 types. It has to be remembered that the cooling (f) Access for erection and maintenance baffles are fitted. This is a frequent cause of

40 4-0 tower is a highly efficient air washer: The proposed location should be studied to icing of nearby paths and roads in winter, ensure that the supplier can indeed erect the when the tower is situated too close to such n (i) Entrainment of fumes from boiler flues r tower, and that the essential normal mainten• routes. It is recommended that a distance of will reduce the pH of the circulating water, ance is possible, with a sufficiently large drain some 6-9 m should be allowed between large 3H! :: •r resulting in rapid deterioration of the piping, to carry both water and sludge, and a cooling towers and roads, according to the a- heat exchangers and the tower itself, due to convenient hose connection to make washing height of the air inlets, because the effective• CM corrosion. down possible during draining. The functional ness of crosswind baffles varies. design features of the water storage basin are 3H1 • (ii) Other processes and effluxes, particularly of prime importance in the ability of the system -E3- oil and diesel fumes, will affect performance to operate consistently and correctly. by coating the system with greasy deposits. Entrainment of cement dust from adjacent FOUNDATION PLAN Effect of tower on its surroundings c building operations is a common source of It is advisable to study the results of the trouble. following effects which may create problems (iii) Contamination by entrainment from within the immediate surroundings of the biological sources such as kitchens and tower: bakeries, laundries, paint spray booths and (a) Condensation of moist air discharge printing processes, will result in organic (b) Downwind vapour drift growths which will attack both the system r and the tower itself. Failure to apply remedial (c) Windage and carryover (d) Noise from fans and water 80 action could result in total blockage and structural collapse of the tower internals. (e) Weight of tower and water i ' 25 (f) Results of accidental leakage i1 (iv) Similar effects can result from blockage by leaves, catkins, bird feathers and droppings. (g) Appearance in relation to surroundings. • 0 Metropolitan Line Berry Lane The high velocity intakes to forced draft fans In all cases, the best solution is to select a are particularly prone to picking up rubbish, location which avoids these problems but. v SECTION C - C leaves and sheets of plastic film. when this is not possible, other measures must be investigated. (v) Contamination of the water can also arise from mixtures of metals in the cooling water (a) Condensation of moist air discharge circuit, resulting in products of corrosion and Since the discharge air is to all intents nearly Fig. 5 Fig 4 in metals dissolving into the water and thus 100% saturated with moisture, at a temperature Sunken induced draft Site plan, soffit plan, foundation plan, section C-C. accelerating corrosive action. In particular, above that of surrounding surfaces, condensa• counterfoil air inlets horizontal 4 zinc (galvanizing) and aluminium should not tion on nearby walls, windows and plant (b) Recirculation dangers bridge, the deck structure needed to be refined. Buildings, large items of plant, other cooling We felt especially that our sketch designs for towers and enclosing walls can all modify the the suspended spans could be improved upon. mass movement of air in such a way as to Forced draft They were based on standard systems of tort- *1 cause recirculation; indeed, the bulk of an counterflow precast beams but we thought that we could I-1 individual large tower, or bank of towers, can pair choose from a wider range as we should need B * A J have this effect on itself, and so it is clear that enough beams to make it economically viable -• the direction of the prevailing wind must be to build special shutters. We were also not w taken into account. Note that the 'prevailing entirely satisfied with the appearance of the wind' for the tower may not be the same as standard beams in this particular case. This that prevailing for the site or area. t bridge will not be seen at a distance, but «WT LOMOmCWAL SEC TON experienced mainly by those driving or ] Another text6 suggests that a tower's exposure walking under it and the shape of the soffit to wind can be taken as open if it is located at X is for that reason particularly important. Fig 5 a horizontal distance of at least 10 times the The south abutment is a long tabletop with the back legs buried in the embankment height of surrounding solid structures. Should We therefore made a special study of decks a tall building or plant item be upwind of the made up from precast beams with in situ i'' tower, the air velocity will decrease as it topping. The criteria are obviously that the precast component should be easy to make, passes the tower with a consequent tendency ^-1 to entrain the warm moist discharge back into transport and erect and that the in situ the downwind air inlet (Fig. 6). component should be easy to shutter and make. The choice of any system, however, Particular instances and partial solutions to will be greatly influenced by its ability to the problems include: distribute the effect of concentrated loads Special 4- nduced over a wide part of the cross-section. Most ii (i) Towers downstream of large buildings draft bridges in this country have to be checked when L<10H: use high velocity discharge counterflow for a load of 180 tons which is concentrated through cones. on a small area, and it is important for (ii) Banks or batteries of towers behind economy that this large load should be screen walls: mount batteries parallel to carried by a much wider part of the deck than prevailing wind, and never in series down the one on which it acts. Our study resulted wind (Fig. 7). Provide fully louvred enclosing in a precast trough unit with an in situ slab walls with ample free area for entering air. on top. It compared well with standard Use only high velocity discharge, preferably systems in our cost estimates and we thought with cones or bonnets. In some instances, a that its advantages, particularly in construc• cure may be achieved by fitting decks or tion, might well in the end make it the baffles at the top of the towers between cheaper deck. The beams can be launched from the northern end onto simple laminated Fig 6 enclosing walls and towers, also between We had a test specimen cast to confirm our design cells; this should be considered palliative and Fig. 2 rubber bearings, and they are stable and form a not as a design solution (Fig. 8). complete platform as soon as they are placed, which is important over the railway. (iii) Single entry crossflow towers should be There is no prestressing to be done on site installed sideways - on to the prevailing wind and the reinforcement in the top slab is very (or modified wind direction due to surround• simple. Shuttering is not needed between ing structures) during critical performance the beams and easily supported over them. periods. Large baffles fitted to top of tower There are no transverse beams except at the can ameliorate recirculation, but again, this is ends, where they are easily cast, but the final not a design feature, merely a solution to a structure is nevertheless very good at problem (Fig. 9). Single entry crossflow distributing loads transversely because of the towers are not recommended for use on high torsional stiffness of the boxes. critical design duties because of the orienta• I- 3 We produced a very refined design for the tion problems. L trough units as they are to be cast under factory (iv) Induced draft crossflow towers have conditions and because each superfluous bit I I high air velocities at the upper sections of of material would be repeated 84 times. To inlet air louvres, and a pressure pattern is make sure that the thin webs could be created which can encourage recirculation n concreted without problems we had a test (Fig. 10). For this reason, extended discharge made. We had a 3m long specimen cast cones are normally fitted to these towers, and • complete with reinforcement and the cable are frequently designed as pressure recovery ducts in their worst position. The test stacks thus aiding fan performance. Single entry crossflow Double entry induced draft crossflow confirmed our design and we shall be able • to provide tenderers with more information (v) Buried, or partially buried, counterflow as well as be able to answerquestions with the induced draft towers exhibit similar effects to confidence that results from having cast one the induced draft crossflow tower. Again, already. The test also gave us a chance for a extended discharge cones should be fitted, preview of the concrete surface that we are together with decks or baffles, at the top of planning. the tower and there should be ample air entry M at the tower base. We studied many complicated structures for l the tabletops. but chose in the end a solid (vi) Forced draft counterflow towers have reinforced slab. A solution for the abutments Fig. 7 lower air leaving velocities so that contributory practically presented itself. The junction Some of the structures for the suspended spans that were compared. factors increase the recirculation risks. Choice between earth embankment and structure is The three upper structures are based on standard precast beams; of location is again very important. Therefore very important, but often difficult to design. the lower is the design that was chosen. Precast beams are shown shaded. the fitting of extended discharge bonnets and Here we could make the tabletops longer and top decks may be of assistance (Fig. 11). bury the hind legs in the embankments. The Ample free air entry area is essential at low trough units need not be adiusted here and level. Forced draft towers with opposed fans all precast beams can be made identical. operated on sequential thermostatic control We presented the scheme to the Royal Fine are subject to recirculation unless fitted with Art Commission in November 1971 and are flow reversal dampers. now (May 1 972) in the final stages of design. Provided that the dangers of recirculation are We have estimated the cost of the project to -u w \J w w vl 2 made known to the tower supplier, he may be be £745.000 or £93 per m . The viaduct is —— . « . able to make allowances for the condition in only a small part of the whole contract which his selection. This will normally result in a i i i i covers the North Orbital Road between SCCTIOM A - A in™- , , . i— MCTMH I • I larger, more costly tower, or increased fan Hunton Bridge and Maple Cross. The horse power, or a combination of both. Hertfordshire County Council Sub Unit of the Fig 8 Addition of discharge bonnets and higher fan Induced draft counterflow increased air entry Forced draft counterflow back to back Eastern Road Construction Unit are designing Cross-sections. The suspended spans (to the left) are partly precast, stacks (cones) can sometimes reduce fan the rest of the works. We hope that tenders the tabletops (to the right) are cast in situ. horse power due to the gain in 'stack effect' will be invited in late autumn; work should 20 but these gains will be marginal. Fig. 3 start on site early next year and last two years. already become the business centre of Paris side of the Seine valley. The forest of Senart competitive industry, and the less technical (a) Free access for entering air The Evry 1 and it will soon be one of the city's densest is just across the river to the east and the old Planning to avoid information is provided, the more commercial Buildings and large items of plant, close residential areas. It can be seen as the first town of Corbeil is one of the member pressures will prevail. proximity of other cooling towers and of solid local city centre of the future metropolis with communes to the south. enclosing walls, can all obstruct entry of air Competition cooling tower Location and planning its express metro and motorway links already The Etablissement Public for Evry new town - to towers. Cooling towers are expected to be capable of established. EPEVRY for short - decided to build this misapplication Solutions include calculation of the free air being positioned almost anywhere: Michael Barclay It is in this context also that the first five new centre in five parts. The 'heart' will contain access area required. For the plant designer towns of the Paris region have been designated the main shopping complex, the main problems on the roof to do this, which is his responsibility, tower - Cergy-Pontoise, Bry-sur-Marne, Melun- entertainment and cultural buildings, and the beside the boiler flues manufacturers must declare the air rate administration. The four central sectors, The 1 965 development plan forthe Paris region Senart, St. Quentin-en-Yvelmes and Evry. behind screen walls requirements of their towers, together with is arguably the most extreme application of a Each lies within 40km of the centre of Paris radiating from the heart, will contain a total Des Gurney air entering and leaving velocities. As a of 20,000 dwellings together with their in the car park professional philosophy which is only now and each should serve a population of the minimum, free area for air flow in any direction schools, local services and open spaces. Each in a courtyard beginning to lose its hold on city planners order of 500,000. (Fig. 1). must be not less than equal to the gross air sector will be built over and around a radial This paper was given at the Cooling Water round the world. The basis for the plan was completely boxed in entry area to the packing. Multiple towers line of the new public transport system and Association Symposium on 28 April 1972. the proposition that half the population of in the basement cannot share this free area - there must be Evry : the first stage include a central pedestrian route. Vehicle and sufficient area for the total airflow at a mean France would live in Paris by the year 2000 The new towns have similar administrative railway access to the town centre will be Introduction in a pit and that Paris should accordingly be planned 1 velocity of perhaps 60-90m per minute. responsibilities and powers, (not unlike those along partly sunken routes through the park• Quoting from an earlier text : 'It is unfortunate underground. as a city of 50m. people who would be highly Consideration of the various types of tower of a British new town development corpora• land between the four central sectors and the that the correct selection and application of This is all fine from the planning and architec• mobile and materially rich. available can be of considerable benefit, along tion but with less democratic control) and distributors will feed into the residential areas cooling towers ... is too frequently given tural view - almost all things can be achieved The ancient city, still separately administered the guide lines given in Table 1 : similar briefs, but they have little else in in a Radburn pattern on a grand scale. scant atttention . . . and so often the cooling provided that the engineer has control over within the boundaries of its ramparts which common. Each professional team has taken It is essential to the whole conception that tower becomes 'nobody's baby'' - yet this is time and money, and the details of planning now roughly coincide with the boulevard its own view of the possibilities open to it and Table 1 : Various tower arrangements the new town centre should become the the ultimate instrument of heat sink for the which affect the proper performance of the peripherique motorway, would remain an of the constraints it should observe. Each effective focus, not only for the four new cooling system - a failure here places the tower. Of course he rarely has this control! according to free air access increasingly depopulated commercial and town will develop in its own way. We central sectors but for the whole conurbation whole plant or process in jeopardy. What is often forgotten is to compare alterna• cultural centre for the new city region which became involved in the first stage of Evry's Number of of 14 communes which will eventually house As engineers, we are expected to play all tive arrangements and types of tower in order would stretch 400 km along the Seine from development and this is the one which is sides with Alternative the half million population. The new public manner of tricks in respect of tower applica• to solve the problem. Fontainebleau to the sea. absorbing Rouen, described here. unobstructed tower transport system, initially conventional buses tion and location ; it is in the hope of providing Le Havre and many other towns in the process. Types of cooling tower air entry arrangements Unlike most British new towns, Evry is planted on their own track, is intended to be one of useful guidance, based on some warning The new motorways and railways to serve and The various types of tower have been classi• astride an agglomeration of existing small the principal means of achieving this aim. examples, that this paper has been prepared. Four Induced draft counterflow link such a conurbation have yet to be defined, towns and housing estates which include fied and their pros and cons outlined in other 1 2 - Fig. 1 let alone constructed. Meanwhile, the present some of the fastest-growing urban areas of There are some remarkable assumptions and Performance expectation texts. . Paris suburban region - the Banlieu - is the region. Evry has been made the head• contradictions implied in the original brief Let us study first the essential expectations We most often encounter towers of the Three Induced draft counterflow exploding with every kind of housing and quarters of the new Essonne Department and which became apparent as we worked on the and fond hopes of the client and user — what mechanical draft type in the following with increased height air commercial development and the small the prefecture was its first building. first sector, but it is first necessary to describe does he want for his money ? configurations: induced draft counterflow. entry - Fig. 1 communes which surround the city are being The centre of the new town will be built on the competition, which is still in progress as For a given thermal duty, a cooling tower is forced draft counterflow, single entry cross- Two See Fig. 2 : overwhelmed by a largely unplanned and this is written, and to explain our participation 450 hectares of flat open land between the expected to provide flow, double entry crossflow. Nowadays, we Adjacent Independent pair of forced unbeautiful growth. in it. A6 (Autoroute du Sud) and the old N7 in a 1 Maximum thermal performance for lowest are not generally concerned with atmospheric draft towers It is in this context that the French government bend of the Seine about 15km south east of In April 1971 EPEVRY invited suitably possible capital outlay natural draft towers unless they be very large, Specially designed set up the mixed-economy Etablissement Orly airport. It will eventually be served by a qualified groups to enter a competition for and of the hyperbolic type; since a previous 2 Long, trouble-free life at minimum cost for induced draft counterflow Public for the Defense area on the northwest branch of the main line railway and by the the design and construction of the first central author has examined these in detail in a maintenance 5 edge of the city a decade ago. La Defense has new city motorway system along the southern sector - Evry 1. The competition was in two recent paper . it is not proposed to repeat Two See Fig. 3: 3 Least possible disturbance to the environ• similar material here. Opposite Double entry induced ment and to other activities in the vicinity Each tower arrangement has its potential draft crossflow of the tower Single entry forced Fig. 1 problems and vicissitudes, and there are some 4 Very often, a tower which looks good, and crossflow Map of region variations on the standard themes which can stays that way throughout its life; perhaps be useful in certain situations. In order to Back to back pair of even an invisible tower! avoid more than a fair share of problems in a independent forced draft I 1111111 zona d urfatniution nouvvllc KNM bOIMV.d'MfMCM VWtt counterflow cantra urbain vow nrrM The client and user, be he architect or given installation, it is necessary to examine I Mllll I (tocaliwtiofi rwi datarminaa; at da k>mn E industrialist, rarely realizes at the planning the location from two main points of view: Induced draft towers ion* d urt»niution noun** vow routore princtpaM Umu npraw rtaional (R.E.R.J nun stage that he wants these things - but he the effect of the location on the cooling with increased air soon remembers when he gets his tower! tower operation and the effect of the cooling entry height VftllOlW We are all very well aware that these are tower on its immediate surroundings. One only See Fig. 4 : conflicting requirements, and their interpreta• Effects of location on tower operation Forced draft counterflow tion, their achievement by careful evaluation It is necessary to evaluate the likely effects on Half of induced draft and compromise, is often left in the wrong i the following parameters essential to cooling counterflow mm hands. LMAY MtllCI tower thermal performance: None: a pit Provided space permits, a Responsibilities (a) Free access for entering air sunken induced draft r AJML B4 Perhaps we should examine the responsibili• counterflow tower with .MM; (b) Danger of recirculation of outlet air to inlet ties of the various involvements. horizontal air inlet baffles Mini (c) Uplift in air wet bulb temperature It is the responsibility of the designers of the at deck level, and discharge inn (d) Air (and hence water) contamination Jill! site, and of the plant which it serves, to air bonnets or cones i ii i ensure that the cooling tower installed is (e) Spoiling of fan performance (Fig. 5).

1 i' suitable for its job in terms of its performance, (f) Access for erection and maintenance Sunken crossflow or U Uff III application, location and appearance. due to the positioning of the tower in forced draft liable to 111111 nun The prime responsibility of the manufacturer relation to its surroundings. excessive recirculation .iiiniii is to provide an efficient and dependable product at a viable price, guaranteed to meet

•OISY-LE-GRAMO the performance which has been specified, and to achieve this by good engineering compromise so that a sensible balance is I i 1 obtained between the conflicting require• • ments, of which he is well aware. MISSY Si LEGER T J While there are, unfortunately, very few I cooling tower engineers, the majority of ! cooling tower suppliers (and there is a wide ! choice - perhaps three dozen in the United Kingdom) employ sales and applications staff T1GERY who are well versed in the problems and who can, when given the opportunity, provide Prtftct sound advice on the application and location of their product. But the salesman can only assess the information which he is given, and CORBEIL this rarely includes layout and planning material or sources of environmental pollution. I I I I 15km At the same time, he must come to terms with Fig.1 6 the commercial pressures imposed by a Standard induced draft counterflow and Induced draft counterflow increased air entry parts - an eliminating round ending in November with the selection of four finalists, and the final round ending in the summer of 1 972 with the selection of the winning group. There would be consolation prizes but no first prize - only the immediate award to the winners of a £60m. contract to finance and build Evry 1 in five and a half years flat. We were invited by Denis Sloan, a French architect with whom we had not worked before, to join him as civil and structural multi engineers in forming the core of a design J3 parking team to make an entry. He had himself been Sltors invited by a French developer, SMCI. who was forming a promotion team to complete the group. We accepted and the group was D" one set of standard panels being sufficient for the lowest leg splice in each panel was raised Due to the programme requirements it was the number of bed spaces and not living Stairs all towers in the family. sufficiently to receive a standard base Lift not possible to check assemble the setting-out rooms. Also there is the problem of service Fig. 4 shows a typical range of towers from connector for attachment to the holding-down B templates for the foundations against the ducts and stores and similar spaces, either the Medium route family. bolts (Fig. 8). corresponding tower base panels. These being part of, or in addition to, the basic area. spanB Member loading variations within a given The use of standard details in this manner templates were fully triangulated, however, The actual dwelling areas were only part of a standard panel, due to differences in design, allowed all the tower body steelwork to be and all connections were made with close whole series of areas that included nett and B windspeed or the number and arrangement of described by a set of tower panel drawings, == tolerance bolts. Each template was assembled gross area ratios for access and service aerials, are catered for as far as possible by with schedules listing the appropriate tubular BF before issue and checked by tape measure• facilities; also, the dwelling densities varied making use of the further advantage of wall thicknesses, end connections or splice ment, the accuracy achieved by the fabricator in different parts of the project. spanM tubular construction, namely the range of types for each tower. being better than 0.02% in overall length. The majority of dwellings for EVRY were to 31 different wall thicknesses associated with Tower and ancillary steelwork followed the be provided as single-level apartments in each tube diameter. This exercise shows the inter-relationship delivery of foundation holding-down steel• various types of block with internal corridor Fig. 2 access. These blocks would vary from low of space and structural zones. Extreme variations of loading beyond the work and setting-out templates, according to Basic planning grid The actual sizes are irrelevant in an overall sense walk-ups to high-rise point blocks. capacity range of the standard member size, a sequence to suit the tower erection To set the background to this planning resulting from severe aerial configurations, are programme. exercise, the following summary embodies accommodated by a more appropriate arrange• [ o a All steelwork was fully galvanized and treated most of the requirements that we thought LIVING m»s 114. ment of standard panels. For example, the to prevent white rust formation. Tubular o 112. flexibility. Fig. 5 illustrates different arrange• Each particular grade of apartment must be M13. 111. sealed later with special galvanized plugs. available in a variety of plan forms, with dual Ml. L14, ments of standard panels resulting in towers MIS. 115. In all, over 3000 tonnes of steelwork were M16. of identical height but having quite different aspect for the larger dwellings. These apart• 116. supplied free on board for the new towers load-carrying capabilities. For the example ments must be able to combine to form all X 6n 7. Standard gusset plate with six-bolt T-connectors under the fabrication subcontract. I 6, .(,.-> shown. Tower 1 has greater strength and possible cluster arrangements and, where Shipping of all materials was arranged by The 1 B1 6 10m of producing variety and not the usual monotonous rows of repetitive blocks. 305(1 1 B2 7 62m The first set of illustrations in Fig. 1 shows simply how three types of dwelling; an o !(£m B3 M1*3»Sr» Y1 3*» apartment, a single storey house and a two M2; mm Y2' m» storey house, can all be planned within the C 95 m Nl SO Y3 3H» same basic dimensional framework. The Yttljll? A N2 »»m Y5 T3-sii* following exercise concentrates on the Apartment 125m' 4/5 Bedrooms ¥6' 3*1m apartment form, as this comprised the vast with ample balcony space and storage N3 btm • Y7 ' 3

zones need to be used, and in the main the Section x-x subsequent plans use a double M unit. When Y»6 25n, a double M unit is used, it must be added to

the dimension of the wall zone to give Open kitchen Closed kitchen dimension L. For instance, if the standard wall-to-wall dimension M is 2.7 m and the Y19t5Sf. n n thickness is 0.2 m the wall-to-wall dimension L d " i is (twice times 2.7 plus 0.2) equal to 5.6m. It is. of course, possible to have various I J dimensions for M in any one project, but the V • 35 Mm j_ | asm | | 75 go | number of permutations rapidly escalates. ra :: The corridor spans have been restricted to Basic Heavy route Medium route Light route three basic dimensions ; the original M plus A ffff \ Kitchen Fig. 3 and B. An important feature to note is the ill _j Fittings Basic tower profiles for Heavy, Medium and Light route families facility to arrange the wall zones so that the corridor can turn a corner. The variable space either side of the service 1 It had been realized that there were certain square towers (Fig. 2). Combining these obtained from the preliminary aerial and map zone gives most of the basic flexibility, but advantages to be gained from the use of effects, it is found that the wind forces acting surveys. even here it was possible to rationalize so that tubular construction, particularly for towers on a triangular tubular tower can be as much Due to the highly competitive nature of the increase in depth of this variable space of triangular plan shape, both in terms of as 50% less than for an equivalent square international telecommunications projects, the is in steps of a sub-module. Fig. 3. area o washing machine economy and appearance. tower constructed of angle members. tower designs had to meet the contract co-ordination, illustrates the full range of areas a dining area b preparation area P. The wind forces attracted by open, latticed The wind forces attracted by the aerials, specification in the most economical manner, or parts necessary for the EVRY dwellings. variable worktops c laundry area towers composed of round tubes are however, are independent of the type of preferably on a station by station basis. At the The coding of these parts is a simple two- measurably less than for towers of similar supporting structure, and the proportion of same time, however, the designs were to be dimensional code for its size. For example a Fig. 5 Kitchen variations are made geometry composed of flat, open members. total wind force carried by individual tower sufficiently flexible to accommodate the final corridor part 'LA' is L long by A span and. Standard kitchen by adding simple worktops and space Furthermore, there is an even greater reduc• members is somewhat greater for triangular tower requirements with the least possible similarly, if s (sub-module) is 0.5m and M is tion in wind force for triangular shaped towers than for square towers. alteration of details and without delaying the 2.7, part MIOs is 2.7m span by 5.0m depth. fabrication programme. i towers compared with the more traditional The final comparison also depends on the Two particular sets of parts are shown in 1 Prefabricated - type of aerial to be supported, since there is a Solutions to satisfy these conflicting require• Fig. 9, and. from these parts, apartments 8. bathroom marked difference in rigidity between the two 8.1 and 8.2 (in Fig. 8) can be planned. The mode ic ments would have been quite simple in lifting tram types of tower. On balance, however, the final isolation. For example, the towers could have bedsitter dwelling is shown in two versions, design forces in corresponding members for been designed individually as final details one of which allows for a staircase or lift insert. ill the two tower types are similar in magnitude. became available from the survey teams, The various living patterns shown in Fig. 4. • • Taking into account the superior compression together with the kitchen and bathroom thereby providing minimum weight structures 1 protective wrap • • load-carrying properties of tubes together with within the framework of a set of consistent sheets. Figs. 5 and 6, were used to evolve •m » • the fact that there are proportionately fewer tower profiles to minimize fabrication costs. the basic grid. These living patterns show how \ Small members in the case of triangular towers, it is This procedure was not possible, however, the particular plan forms accommodate the N! • • \ Kitchen found that the weight t>f these towers is without seriously delaying the fabrication family's changing requirements. The standard substantially less than for square ones of programme. Alternatively, a complete set of kitchen in Fig. 5 is in fact only standard for 2 Basic service wall • similar dimensions. final tower designs could have been produced the complicated cabinets; the additional As a confirmatory exercise, parallel designs prior to receiving the final station details by space and worktops are uncomplicated and were developed, during the pre-tender stage basing all designs on the tallest possible tower so can be very flexible. The standard bathroom •re ItonoM flltlistl - of the main contract, for sets of towers based having the most severe aerial loading. Such a is a contained unit and only needs to be on the two types discussed. Tenders were solution would allow fabrication to proceed variable for the small dwelling when the unhindered, but would not have been internal partition is removed. This is for two obtained for both fabrication and erection, Partition economic. and comparative shipping costs established. reasons: firstly the restricted area of a small Basic removed dwelling necessitates the use of one door for small The result indicated a clear economic advan• The compromise solution finally adopted was f Bathroom dwelling tage in the use of tubular towers. to group the towers into three distinct only and, secondly, the extra space created families according to the primary aerial system provides a washing machine or laundry space. Development of standardized to be supported : 3 tower designs 29 Heavy route towers - 6 GHz microwave The need to obtain tenders for the fabrication system 3 Integrated and supply of tower and ancillary steelwork service wall Fig. 4 before final details of the structures could be 48 Medium route towers - 2 GHz microwave Fig. 6 Typical range of Medium route towers made available, meant that initial designs had' system Small kitchen and standard bathroom to be based on provisional information 1 6 Light route towers - VHF system. The dwelling arrangements in Figs. 7, 8. 10 and 11 all show possible apartment layouts from the initial route surveys, and the systems 50 —7.41 7.1 that conform to the basic grid, and, in addition Tubular steel planning operations, to bringing the network y 2 5 livins rooms 7 2 livini to these, many more can be evolved. As into service. The pre-contract estimating was Square towers previously noted, the structural zone is only microwave towers based on a preliminary aerial survey over 7.3 Triangular towers 7.1 used when necessary and, in the majority of 565 km. of the network, the remainder being i cases, a double span slab has been used. for Nigeria covered by map surveys, but the final station Fig. 12 shows how blocks can be increased locations and optimum tower heights could in size and how the various dwellings are not be determined until the results of a Mike Shears detailed ground survey had been processed. : combined to form continuous blocks. members The photographs of the architect's model The ground survey teams were able to begin

i clearly show how the blocks of apartments This article appears in Tubular Structures field operations in the autumn of 1 968 in all were to be articulated and varied in order to no. 21 and is reproduced here with the regions except the Eastern States, where access to the sites was not possible until early turnet J be totally integrated into many different editor's permission. 7&L m situations. 1970. Due to the requirements of the main contract programme, however, the tower 1 The drawings were prepared by Bryan Introduction designs for fabrication tenders had to be 7 A 5 living HUM Seymour and David Lay. The microwave radio towers described in this article form part of a contract for the provision based on provisional heights. of a microwave radio relay system for Step III The final tower heights and orientations —i became available, route by route, at intervals, 2 livini rooms of the Nigerian National Telecommunications n + servicserv« e inse' Development Plan. The main contract, one of as information was received from the survey teams during the first few months of the • the largest of its kind ever placed with a \ currency of the fabrication programme. Design British company, was awarded to The Round members General Electric Company Ltd. in 1968 and, details were then issued to the fabricator in batches according to a predetermined Dwelling arrangements Each variant can be to the opposite hand in addition to the radio equipment, comprises the supply and installation of aerial supporting sequence. The tower design philosophy structures, aerial systems, power supply adopted to deal with these circumstances is equipment, equipment buildings and all described later in this article. Balcony variation : , ___ associated civil works. Tower design specification The main contract specification called for 0 C 4 living 0 0-2 0-E • oom- 0 2 * living roomi 1 Ii vine roo IT O.J bakonbalconyi variation 8 bed si The Step III microwave and VHF radio relay self-supporting towers at the terminal stations Q ? 3 living rooms system utilizes 93 entirely new stations, as Fig. 2 Solidity ratio this variation can be used on the network, but allowed consideration of with other dwelling : well as the refurbishment of existing facilities guyed masts for the intermediate, or repeater Drag coefficients for latticed towers , f J and the addition of updated aerial systems at stations. In view of the wide range of tower f some link stations, to provide a network heights and the variety of aerial arrangements • - covering nearly 4000 route kilometres. The proposed, however, and coupled with the For the consideration of tower rigidity, new system will be integrated with existing the operational design requirements were :: limited site area available at a number of the transmission systems and telephone exchanges stations, it was finally decided to provide expressed in terms of displacement of the in Nigeria, many of which, including the self-supporting towers throughout. aerial mounting point in azimuth and elevation, 760 km. Step I network, were also provided The specification also required that the taking account of the relative displacements by The General Electric Company Ltd. When supporting structures be designed with of the aerial with respect to the supporting completed towards the end of 1 972, the sufficient strength and rigidity to permit structure, such that the resulting radio beam network will connect all the large centres of displacements would not exceed the half- ••• system operation without noticeable trans• : population in Nigeria, as well as many smaller mission degradation under the action of wind power points at the specified design wind communities, to give the entire country an velocities. J velocities of 38m/s for structures located advanced telephone service. The nationwide north of the Niger and Benue Rivers and Two types of microwave equipment are used f t extent of the system is indicated by the map 33.5 m/s for structures located south of these in the system with transmission frequencies $H 3 living room: roorr in Fig. 1. which also gives the transmission 8.i t» rivers. In each case the design wind gust of 6 GHz and 2 GHz, both utilizing 3.65m frequencies adopted on the various routes of velocities were defined at 10m above ground diameter GEC parabolic dish aerials, in : the network. level, and were assumed to vary with height addition to Yagi type aerials for VHF trans• 5 * The Step III contract is a 'turnkey' project in according to a power law profile. missions. The specified radiated beam

8.S I8."4 8 which The GEC is responsible for all aspects displacement requirements were as follows:

Fig. 8 f . 8.3 Dwelling arrangements 8.1 8.4 8.4 Fig.1 Aerial frequency Total radio beam Tower Nigeria Step route map

6GHz ±0.55° 0.45° NIGER 2 GHz ±1.30° 1.20° SOK0TO r VHF ±10° 10° M8- L14s L14<

GUSAU Wind loading The resulting wind forces acting on the tower body structure were obtained using composite drag coefficients consistent with the plan shape and the type and arrangement of members used in the construction. The drag See 8. BUSSA coefficients used in the design exercises were LA LA expressed in terms of solidity ratio ; the ratio of area of exposed steelwork to envelope area of NIG/ERIA that portion of windward tower face under consideration (Fig. 2). The effect of angle of incidence of the wind to a tower face was LSI L10; allowed for by means of amplification factors, HI* * L0K0J again expressed in terms of solidity ratio, y ) / t^^i^SMUliBU »*** MAKURDI applied to the calculated drag coefficients. The wind forces produced by the aerial arrays See 8.2 ! CAMEROON were determined from wind tunnel measure• See 8.1 DGOJA ments supplied by the manufacturers, and the ENIN CITY ENUGU >»*••.. forces acting on individual structural members, ABAC AMI" The Nigerian National Telecommunications Plan Step 3 : ONITSHA/V., 6 GHz broadband radio systems ladders and feeder cables, etc., were assessed SAFE Li 2 GHz broadband radio systems using published values of lift and drag •UMUAHIA; 450 MHz narrowband radio systems .12circuit open wire line systems coefficients for isolated members. Fig. 9 ------VHP narrowband radn systems Choice of tubular towers IIXXKX 6 GHz equipment in service (step 11 Area co-ordination HARCOURT +•••••• 2GH, equipment in service The decision to use tubular steel members for for typical dwelling the construction of the towers was reached GEC-AEI Telecommunications Ltd at the pre-tender stage of the main contract. 1C to give residual and peak shear strength detected were not those on which (e) Neglecting the work done in internal parameters: movement took place. However, move• deformation in the calculation probably (a) The situation immediately prior to failure ment could have been continued by a gives rise to serious errors (particularly in in 1953 (both with and without the compound movement where the remnants respect of the first failure, where a progres• progressive failure approximation) of the 1883 slip moved first, precipitating sive failure mechanism was probably in action). However, until a method of 1 living (b) The situation some weeks after failure further movement of the remainder. If this were the case, the true residual angle of analysis based on the stress/strain/ (c) The geometry existing in 1956 shearing resistance would be higher than volume change behaviour of the soil is (d) The geometry existing in 1966 that calculated from the stability of the available, this inaccuracy must be and the results of these analyses are presented whole mass, accepted. in Table 1 below with the results of the stability (d) The neglect of end effects in the stability analysis of the regraded profile included for calculations is thought to be reasonable Additional information comparison. as the slip is very wide and the geometry In 1970, regrading effectively destroyed the The residual strength analysis was carried out is sensibly constant throughout this width. Miramar landslide as the subject of further first and it was then established that the study, but during this process considerable stresses in the 1883 slip remnants were evidence was brought to light which assisted appropriate to a a 'r of 11 in 1953. Using in the interpretation of the earlier surface observations and borings. this strength in an analysis (Fig. 1) gave peak 3 living rowns parameters of C' = 0. 0'=2O° in the intact clay (along the slip surface from B to D) but, Conclusions following a suggestion by Hutchinson that The study of the stability of the Miramar stress relief may have allowed strains along landslide, carried out as a part of the overall Point cluster used for linear continuity the interface with the Oldhaven Beds, study of the cliffs at Heme Bay, has yielded a number of important pieces of data of the reducing the shear strength to the residual Fig. 10 strength behaviour of London Clay. These are : value (along B to C). a further computer run Dwelling arrangements gave values of C'=450. o'=20 along the (a) Peak strengths: Two alternative assess• remainder of the failure surface. CD. This is ments of the influence of progressive thought to simulate the maximum influence failure have given realistic upper and Cluster variations of a possible progressive failure mechanism1. lower bounds for the peak shear strength parameters of London Clay in the field at Possible errors high stress levels where there were no 5 ,vm8 f0 Inevitably in a survey such as this, where the previous data. 113 ' conclusions are based on incomplete evidence, (b) Residual strengths: A large number of various alternative interpretations of the analyses showed that in the field, as in available data may be made and an assessment 2 Bishop's ring shear tests , the residual Stairs of the possible errors assists in checking the I J 2 * living rooms angle of shearing resistance is stress validity of the results obtained. These dependent and values have been estab• possibilities are: lished at hitherto unprecedented stress (a) That unloading the failure surface may levels by means of a very well documented 2 temporarily increase the residual strength . Fig. 7 and instrumented case history. The mean effective stress on the slip View of 1953 slip from the surface has been reduced, although the centre looking east References movements have probably been sufficient Photo: Courtesy Soil Mechanics Ltd. (1) BISHOP, A. W. The influence of progres• to restore the minimum value. Fig. 8 sive failure on the choice of the method of (b) Gross errors have been made in the Failure surfaces of 1953 slip stability analysis. Geotechnique. 21 (2), evaluation of pore pressures. This must pp. 168-172, 1971. 11 1 3 Itvins |2 * living roomi always remain a valid criticism where (2) BISHOP, A. W. and others. A new ring End of corridor unit observations are lacking, but the model shear apparatus and its application to the assumed from the recent records would measurement of residual strength. Geotech• seem to be most reasonable. nique. 21 (4). pp. 273-328. 1 971. (c) Gross errors have been introduced by (3) DUVIVIER, J. Cliff stabilization works in incorrect determination of the ground or London Clay. Journal of the Institution of slip-surface levels. In the case of the Civil Engineers. 14 (October), pp. 412-426, earliest profiles, the ground levels are 1940. Fig. 11 probably accurate to within ±2m, and Dwelling arrangements (4) HUGHES, M. J. Heme Bay stability study this would appear to be sufficient for the - report on the stratigraphical micropalaeon- analysis. The failure surface and most tology. Institute of Geological Sciences recent ground surface levels are known to Report no. PD170/31. The Institute. 1970. a much greater accuracy and alternative Recessed porches toe positions chosen in the analysis do A' (5) HUTCHINSON. J. N. A survey of the not significantly affect the results. It is s. coastal landslides of Kent. Building Research highly unlikely that the failure surfaces Station Note EN/35/65. BRS, 1 965. (6) HUTCHINSON. J. N. The stability of cliffs composed of soft rocks with particular Table 1 : Results of stability analyses reference to the coasts of SE England. Ph. D. Thesis. Cambridge, 1 965. Profile Average Average normal Inclination of Average ru (7) HUTCHINSON. J. N. and H UGHES. M.J. 0 date shear stress effective stress value intersliceforces ** Comments *** The application of micropalaeontology to the 2 2 lbf/ft lbf/ft location of a deep-seated slip surface in the London Clay. Geotechnique. 18 (4), pp. 1953* 3050 1020 .33 15 to 18° See note 1 508-510, 1968. 1953 680 3106 .40 9.76° 0 'm= 1 2.3° pore (8) JAMES, P. M. Time effects and progres• pressures assumed sive failure in clay slopes. Ph. D. Thesis, 1956 615 3223 .38 9.40° 0'm=1O.8° Imperial College of Science and Technology. 1966 618 3030 ,37 9.63° o'm=11.5° 1971. 1970 528 2563 .43 7.40° 0'm=11.6° (9) KENNEY, T. C. An examination of methods for calculating slope stability. M. Sc. * Two alternative toe positions have been taken: (a) passes along the old slip surface Thesis, Imperial College of Science and of the 1883 slip, and (b) passes through the landslide debris. The most critical was Technology, 1 956. Traditional found to be (a). 0 'r along old slip surface assumed to be 11 °. 24 living corridor (10) MORGENSTERN. N. R. and PRICE, V. E. ** Taken as acting at a uniform inclination to the horizontal and evaluated in terms of The analysis of the stability of general slip total stresses. surfaces. Geotechnique. 15 (1), pp. 79-93, *** Obviously, the mobilized angle of shearing resistance 0'm is equal to the residual 1965. Articulated corridor with angle if the factor of safety is unity. (11) HUTCHINSON. J. N. and BHANDARI, An example of cluster development Some dwelling integration possibilities individual entrances Note 1: With residual strengths along AB : C'peak=0 and T= 1 675, an'=4600 along BD, R. K. Undrained loading, a fundamental however, with residual strengths along AC: C peak = 450 with T=1200. Wiu,i,iiiirt.,rll clay is weathered brown to a depth of forward some 12m and showed a marked comparatively high effective stress levels, pore pressures under the 'intact' ridge block Oldhaven Sandstone 8 approximately 13 m. and at a greater depth preferential movement at its western end. By since the existing data by James was for were probably kept up by flow through the Fig. 2 the colour changes again from a grey-brown 1 933 (4th series) the ridge was so eroded very small slips in railway cuttings at low horizontal sandy layers. One effect of these Section in 1 950 and after 1 953 slip to a bright grey-blue. In general, the penetra• that it was no longer identifiable. effective stresses. high pressures, caused by seepage from above, was to prevent the tidal fluctuations tion of weathering from the cliff face is Landslide of 1953 Site investigation of pressure in the sands below from having negligible. Probable profile m 1953 Early in the morning of 4 February 1953 Clusters of borings were placed systematically any effect on the stability. The situation with Ground surface from Occurrence of large landslides another major landslide took place involving down selected section lines through both photos 1956 the tide at its lowest ebb was the most critical 100 Feel Possible surface ol 1803 slip These cliffs have a history of erosion and have the same stretch of cliff. This time approxi• slipped and intact clay slopes. A visual exam• and has been taken for analysis. Pieiometric pressures on slip surface been subject to considerable study and mately 25m width of cliff top was lost and ination of continuous undisturbed samples This toe heate mar indicate that 3 stabilization work in the past. Generally they photographs (Fig. 7) taken after the failure throughout the depth of the first boring at Surveys moiement on 1803 slip surface London Clay caused a ii.oee.weni on the n» degrade by a process of mudflow formation, reveal this slipping down between sharply each location enabled features of interest such A very accurate survey of the ground profile slip surface but from time to time deep seated failures dipping failure surfaces to form a near as failure surfaces (Fig. 8) to be located, and was carried out in 1966 and further surveys B'oct have occurred. Such failures have always horizontal graben. while the original cliff face several piezometers were installed at each of a section chosen in the westerly half of the O.D.Level occurred in stretches of cliff capped by sand was pushed forward intact to form a sharp location. Flow nets were drawn from the slip were carried out from RAF photographs Oldhaven Sandstone and gravel ('Head') deposits. It has been crested ridge. The forward movement of this piezometer readings and well back from the dated 1950 and 1956. (This section differs 3 held that these comprise a reservoir for water, block considerably disturbed the debris at the edge of the cliff it was shown that the flow slightly from that of Hutchinson6,7). Taking although an alternative explanation may be toe (remnants of the 1 883 slide). By 1956 was near vertical. Both from the flow nets for the 1950 profile as a close approximation to Fig. 3 that they do not allow mudflow activity to any the crest of the ridge had moved forward 10 m, undisturbed sections, and by a visual examina• the profile at failure, it was possible to Section in 1 956 great extent and this causes oversteepening once again showing preference for movement tion of the samples, it was evident that the reconstruct the slip surface and Fig. 2 shows of the cliff by toe erosion. The elevation of the at the westerly end. and a further 15m of vertical permeability in the lowest 6 m of the both this and the inferred geometry soon after failure. In contrast to the negligible effect of Outcrop of turf and unde- r "f Sections in 1966 profile head deposit-, riteaied M 1970 • tides on the pore pressures after failure, the Reanded 1970 Groben Sloe*, and debris fro* 1966 and 1970 stability of the Miramar slip in 1953 was 100 Feel profile degradation of rear scarp MM! Proooe-e potitien m 1988 5«Mtf ff/rrf JrW jeopardized by the tidal surge a few days 1898 1933 Outcrop of Horit block in 1970 ikfii rttreded before in two ways; both by increased toe 0fltf m»* PieiomeirK pre.sures an slip surtoce tort**'" erosion and by a marked increase in the pore surface after rearodina. • CP Flood •«!! pressures in the Oldhaven Beds. P Sea .tan k> robin 8 loci Slipped Block I I*. 11. Movements of slipped mass O.D Level London CI a -/ \ y I Continuation of movement was ensured, both Oldhaven Sandstone I by undrained loading (falls from the rear scarp11) and by continued erosion and cross sections based on the ground profile in 1956 Fig. 4 and 1 966. These are shown in Figs. 3 and 4. Sections in 1966 and 1970 ... It appears likely that the ridge moved forward KM again in the period 1966-1970 when the investigations took place, and the magnitude 19 Top Of Cliff Area of .lope of this movement is estimated to be about 5 m. Mlromar Total erosion of 1883 H 1*l Bolton cf Cliff Gross - co»ered art a 0 Fig. 5 shows how the crest has moved during slip m fifty yeari Top of slope Tree - MVtrM area this period. A total movement of about 30 m 9«,e - 966 • : 4 7 Bottom of slope is inferred. The micro-palaeontology - 966 i970 showed that the graben had suffered a vertical 1996-1906 (Earlier slip! Sana ana Mua KN displacement of at least 1 7.4 m. $: - - ana Fig. 5 day o" fore*»ore Initial analysis Estimate of nutc'oe seel.on cnoser rate of movement The back analysis technique for obtaining of crest with time shear strength parameters is well established 0 10 20 30 40 SO and to complement James' data 8 (which is 0 probably the most comprehensive to date although suffering from a paucity of field observation and dealing only with relatively shallow slides) all of the available slides on JOOO ine the Heme Bay coastline were analysed to N obtain the residual, and, in the case of the Miramar landslide, peak shear strength Miramor parameters. The Kenney9 method (Program MM OA800) was used, at first giving satisfactory Bo, - • (19661 •tarn* B«, M.r« results, but it did not give a convergent solution Fig. 6 mtm Bo, Hiromar tl»C) when applied to the 1966 profile of the Variation of Miramar slide. mean shear stress on failure surfaces :i9TOi RiisjrodtfJ l%tab>ii.»«dl 1907 1959 Further analyses with the mean normal Hole Plan dttails offer 0 S KttH Sheet XXIV9 Further results were then obtained from a 1000 ?ooo sooo effective stress Avorraajs* Normal EffOCIiv* Sunt* »l/ttJ Fig. 1 FEE' computer program written by the author using Changes in cliff at Miramar site the Morgenstern and Price procedure10 (Program OA808). Four cases were analysed 13 undisturbed clay was substantially lower than underlying sandstone appears to control the movement took place in the following decade. in the overlying material, but the presence of Position ol slip from pnclogropfis, I953 Section in 1950 A study of degree of non-circularity of the failure surfaces Two large mudflows formed and emerged sandy and silty layers probably greatly - Ground prof lit from air photos, 1950 of such slips. around each end of the intact block. increased the horizontal permeability. It was - Possiblf seconddrs slip surtdce a large landslide Position of Miramar Landslide Initial studies also logical that the highly disturbed landslide - Pieiemetric surface based on moan part debris should also be comparatively very pressures dorrn undisturbed profile For a length of approximately 1 00 m, coincid• An initial examination of this landslide (called at Heme Bay, Kent permeable. A model of pore pressures in the Approximate position of 883 ing with the outcrop of the Oldhaven Beds on the Miramar Landslide, after a nearby hotel, slip surface from 0 S plans landslide debris being very high, but drawn the foreshore, the cliffs have failed twice in part of the grounds of which were lost) by Pieiomelnc surface based on pore rjoiet 5 6 7 down with a high hydraulic gradient into the recorded history and the evidence shows Hutchinson - - revealed that the landslide pressures in sandstone during tiddt surge Ted Bromhead underlying sands, corresponded closely to the certain similarities in the behaviour of both had taken place on a highly non-circular observed pressures and was therefore very • llernotire positions of toe slides. A brief summary of the information failure surface and an estimate of the displace• London between these limits This paper won the 1972 Cooling Prize of reasonable, and the pore pressures acting along iritical e^merges apparent from the Ordnance Survey maps will ment was obtained by a study of the microfossil Clay the British Geotechnical Society. the failure surface were much higher than the serve to emphasize these. Fig. 1 is a site plan succession7. In this study, the three major tidally controlled pressures observed in the Stratigraphy based on these maps. landslides in these cliffs were investigated in Oldhaven Sandstone sands below. The East Cliffs at Heme Bay run for several Landslide of 1883 a similar, although more exhaustive fashion, Deeply penetrating crocks miles In an east to west direction, rising to a The first edition of the Ordnance Survey but it was unfortunate that two of these had In view of these observations, it was possible -i95J si,p surtoce Section immediately maximum height of 38m OD, and are shows no trace of any failure but, between already been partially regraded, and the true to infer that the distribution of pore pressures -Appronmate position of 1963 slip surface (from 0 5 plans) after 1953 slip composed of the lower beds of the London then and the 2nd series in 1 896, majorchanges pore pressure distribution before these works was similar in 1966 to that observed after were carried out was impossible to judge. regrading in 1 970, and that the pore pressures -Profile in I950 Clay. A weakly cemented sandstone, the had taken place, with local history placing a -Attuned pore pressure? sometime alter failure However, an estimate could be made, and it existing at the earlier dates would have been Oldhaven Beds, underlies the London Clay failure in 1 883. About 20m of the cliff top This area reported very disturbed ofler and their interface dips slightly from east to slid downwards and a ridge and graben was thought worthwhile to attempt analyses at least as high, if not higher, caused by the slip toe position therefore unknown on earlier profiles in order to provide some percolation of water from the surface down • :te west, allowing the sands to form steep cliffs structure was visible, similar to that of the Sliding Block -*» Various possible positions of toe in the east, above which the London Clay second failure discussed below. In the years field data on the behaviour of the residual open joints in the slipped mass and undrained London VBietk 1 *v londtiide.'Debriv/ strength parameter for the London Clay at loading ' by falls from the rear scarp. The Xr^y^"^-' Lono.iide ueoi thins out. and lies at depth to the west. The between 1896 and 1906 the ridge moved > Wiu,i,iiiirt.,rll clay is weathered brown to a depth of forward some 12m and showed a marked comparatively high effective stress levels, pore pressures under the 'intact' ridge block Oldhaven Sandstone 8 approximately 13 m. and at a greater depth preferential movement at its western end. By since the existing data by James was for were probably kept up by flow through the Fig. 2 the colour changes again from a grey-brown 1 933 (4th series) the ridge was so eroded very small slips in railway cuttings at low horizontal sandy layers. One effect of these Section in 1 950 and after 1 953 slip to a bright grey-blue. In general, the penetra• that it was no longer identifiable. effective stresses. high pressures, caused by seepage from above, was to prevent the tidal fluctuations tion of weathering from the cliff face is Landslide of 1953 Site investigation of pressure in the sands below from having negligible. Probable profile m 1953 Early in the morning of 4 February 1953 Clusters of borings were placed systematically any effect on the stability. The situation with Ground surface from Occurrence of large landslides another major landslide took place involving down selected section lines through both photos 1956 the tide at its lowest ebb was the most critical 100 Feel Possible surface ol 1803 slip These cliffs have a history of erosion and have the same stretch of cliff. This time approxi• slipped and intact clay slopes. A visual exam• and has been taken for analysis. Pieiometric pressures on slip surface been subject to considerable study and mately 25m width of cliff top was lost and ination of continuous undisturbed samples This toe heate mar indicate that 3 stabilization work in the past. Generally they photographs (Fig. 7) taken after the failure throughout the depth of the first boring at Surveys moiement on 1803 slip surface London Clay caused a ii.oee.weni on the n» degrade by a process of mudflow formation, reveal this slipping down between sharply each location enabled features of interest such A very accurate survey of the ground profile slip surface but from time to time deep seated failures dipping failure surfaces to form a near as failure surfaces (Fig. 8) to be located, and was carried out in 1966 and further surveys B'oct have occurred. Such failures have always horizontal graben. while the original cliff face several piezometers were installed at each of a section chosen in the westerly half of the O.D.Level occurred in stretches of cliff capped by sand was pushed forward intact to form a sharp location. Flow nets were drawn from the slip were carried out from RAF photographs Oldhaven Sandstone and gravel ('Head') deposits. It has been crested ridge. The forward movement of this piezometer readings and well back from the dated 1950 and 1956. (This section differs 3 held that these comprise a reservoir for water, block considerably disturbed the debris at the edge of the cliff it was shown that the flow slightly from that of Hutchinson6,7). Taking although an alternative explanation may be toe (remnants of the 1 883 slide). By 1956 was near vertical. Both from the flow nets for the 1950 profile as a close approximation to Fig. 3 that they do not allow mudflow activity to any the crest of the ridge had moved forward 10 m, undisturbed sections, and by a visual examina• the profile at failure, it was possible to Section in 1 956 great extent and this causes oversteepening once again showing preference for movement tion of the samples, it was evident that the reconstruct the slip surface and Fig. 2 shows of the cliff by toe erosion. The elevation of the at the westerly end. and a further 15m of vertical permeability in the lowest 6 m of the both this and the inferred geometry soon after failure. In contrast to the negligible effect of Outcrop of turf and unde- r "f Sections in 1966 profile head deposit-, riteaied M 1970 • tides on the pore pressures after failure, the Reanded 1970 Groben Sloe*, and debris fro* 1966 and 1970 stability of the Miramar slip in 1953 was 100 Feel profile degradation of rear scarp MM! Proooe-e potitien m 1988 5«Mtf ff/rrf JrW jeopardized by the tidal surge a few days 1898 1933 Outcrop of Horit block in 1970 ikfii rttreded before in two ways; both by increased toe 0fltf m»* PieiomeirK pre.sures an slip surtoce tort**'" erosion and by a marked increase in the pore surface after rearodina. • CP Flood •«!! pressures in the Oldhaven Beds. P Sea .tan k> robin 8 loci Slipped Block I I*. 11. Movements of slipped mass O.D Level London CI a -/ \ y I Continuation of movement was ensured, both Oldhaven Sandstone I by undrained loading (falls from the rear scarp11) and by continued erosion and cross sections based on the ground profile in 1956 Fig. 4 and 1 966. These are shown in Figs. 3 and 4. Sections in 1966 and 1970 ... It appears likely that the ridge moved forward KM again in the period 1966-1970 when the investigations took place, and the magnitude 19 Top Of Cliff Area of .lope of this movement is estimated to be about 5 m. Mlromar Total erosion of 1883 H 1*l Bolton cf Cliff Gross - co»ered art a 0 Fig. 5 shows how the crest has moved during slip m fifty yeari Top of slope Tree - MVtrM area this period. A total movement of about 30 m 9«,e - 966 • : 4 7 Bottom of slope is inferred. The micro-palaeontology - 966 i970 showed that the graben had suffered a vertical 1996-1906 (Earlier slip! Sana ana Mua KN displacement of at least 1 7.4 m. $: - - ana Fig. 5 day o" fore*»ore Initial analysis Estimate of nutc'oe seel.on cnoser rate of movement The back analysis technique for obtaining of crest with time shear strength parameters is well established 0 10 20 30 40 SO and to complement James' data 8 (which is 0 probably the most comprehensive to date although suffering from a paucity of field observation and dealing only with relatively shallow slides) all of the available slides on JOOO ine the Heme Bay coastline were analysed to N obtain the residual, and, in the case of the Miramar landslide, peak shear strength Miramor parameters. The Kenney9 method (Program MM OA800) was used, at first giving satisfactory Bo, - • (19661 •tarn* B«, M.r« results, but it did not give a convergent solution Fig. 6 mtm Bo, Hiromar tl»C) when applied to the 1966 profile of the Variation of Miramar slide. mean shear stress on failure surfaces :i9TOi RiisjrodtfJ l%tab>ii.»«dl 1907 1959 Further analyses with the mean normal Hole Plan dttails offer 0 S KttH Sheet XXIV9 Further results were then obtained from a 1000 ?ooo sooo effective stress Avorraajs* Normal EffOCIiv* Sunt* »l/ttJ Fig. 1 FEE' computer program written by the author using Changes in cliff at Miramar site the Morgenstern and Price procedure10 (Program OA808). Four cases were analysed 13 to give residual and peak shear strength detected were not those on which (e) Neglecting the work done in internal parameters: movement took place. However, move• deformation in the calculation probably (a) The situation immediately prior to failure ment could have been continued by a gives rise to serious errors (particularly in in 1953 (both with and without the compound movement where the remnants respect of the first failure, where a progres• progressive failure approximation) of the 1883 slip moved first, precipitating sive failure mechanism was probably in action). However, until a method of 1 living (b) The situation some weeks after failure further movement of the remainder. If this were the case, the true residual angle of analysis based on the stress/strain/ (c) The geometry existing in 1956 shearing resistance would be higher than volume change behaviour of the soil is (d) The geometry existing in 1966 that calculated from the stability of the available, this inaccuracy must be and the results of these analyses are presented whole mass, accepted. in Table 1 below with the results of the stability (d) The neglect of end effects in the stability analysis of the regraded profile included for calculations is thought to be reasonable Additional information comparison. as the slip is very wide and the geometry In 1970, regrading effectively destroyed the The residual strength analysis was carried out is sensibly constant throughout this width. Miramar landslide as the subject of further first and it was then established that the study, but during this process considerable stresses in the 1883 slip remnants were evidence was brought to light which assisted appropriate to a a 'r of 11 in 1953. Using in the interpretation of the earlier surface observations and borings. this strength in an analysis (Fig. 1) gave peak 3 living rowns parameters of C' = 0. 0'=2O° in the intact clay (along the slip surface from B to D) but, Conclusions following a suggestion by Hutchinson that The study of the stability of the Miramar stress relief may have allowed strains along landslide, carried out as a part of the overall Point cluster used for linear continuity the interface with the Oldhaven Beds, study of the cliffs at Heme Bay, has yielded a number of important pieces of data of the reducing the shear strength to the residual Fig. 10 strength behaviour of London Clay. These are : value (along B to C). a further computer run Dwelling arrangements gave values of C'=450. o'=20 along the (a) Peak strengths: Two alternative assess• remainder of the failure surface. CD. This is ments of the influence of progressive thought to simulate the maximum influence failure have given realistic upper and Cluster variations of a possible progressive failure mechanism1. lower bounds for the peak shear strength parameters of London Clay in the field at Possible errors high stress levels where there were no 5 ,vm8 f0 Inevitably in a survey such as this, where the previous data. 113 ' conclusions are based on incomplete evidence, (b) Residual strengths: A large number of various alternative interpretations of the analyses showed that in the field, as in available data may be made and an assessment 2 Bishop's ring shear tests , the residual Stairs of the possible errors assists in checking the I J 2 * living rooms angle of shearing resistance is stress validity of the results obtained. These dependent and values have been estab• possibilities are: lished at hitherto unprecedented stress (a) That unloading the failure surface may levels by means of a very well documented 2 temporarily increase the residual strength . Fig. 7 and instrumented case history. The mean effective stress on the slip View of 1953 slip from the surface has been reduced, although the centre looking east References movements have probably been sufficient Photo: Courtesy Soil Mechanics Ltd. (1) BISHOP, A. W. The influence of progres• to restore the minimum value. Fig. 8 sive failure on the choice of the method of (b) Gross errors have been made in the Failure surfaces of 1953 slip stability analysis. Geotechnique. 21 (2), evaluation of pore pressures. This must pp. 168-172, 1971. 11 1 3 Itvins |2 * living roomi always remain a valid criticism where (2) BISHOP, A. W. and others. A new ring End of corridor unit observations are lacking, but the model shear apparatus and its application to the assumed from the recent records would measurement of residual strength. Geotech• seem to be most reasonable. nique. 21 (4). pp. 273-328. 1 971. (c) Gross errors have been introduced by (3) DUVIVIER, J. Cliff stabilization works in incorrect determination of the ground or London Clay. Journal of the Institution of slip-surface levels. In the case of the Civil Engineers. 14 (October), pp. 412-426, earliest profiles, the ground levels are 1940. Fig. 11 probably accurate to within ±2m, and Dwelling arrangements (4) HUGHES, M. J. Heme Bay stability study this would appear to be sufficient for the - report on the stratigraphical micropalaeon- analysis. The failure surface and most tology. Institute of Geological Sciences recent ground surface levels are known to Report no. PD170/31. The Institute. 1970. a much greater accuracy and alternative Recessed porches toe positions chosen in the analysis do A' (5) HUTCHINSON. J. N. A survey of the not significantly affect the results. It is s. coastal landslides of Kent. Building Research highly unlikely that the failure surfaces Station Note EN/35/65. BRS, 1 965. (6) HUTCHINSON. J. N. The stability of cliffs composed of soft rocks with particular Table 1 : Results of stability analyses reference to the coasts of SE England. Ph. D. Thesis. Cambridge, 1 965. Profile Average Average normal Inclination of Average ru (7) HUTCHINSON. J. N. and H UGHES. M.J. 0 date shear stress effective stress value intersliceforces ** Comments *** The application of micropalaeontology to the 2 2 lbf/ft lbf/ft location of a deep-seated slip surface in the London Clay. Geotechnique. 18 (4), pp. 1953* 3050 1020 .33 15 to 18° See note 1 508-510, 1968. 1953 680 3106 .40 9.76° 0 'm= 1 2.3° pore (8) JAMES, P. M. Time effects and progres• pressures assumed sive failure in clay slopes. Ph. D. Thesis, 1956 615 3223 .38 9.40° 0'm=1O.8° Imperial College of Science and Technology. 1966 618 3030 ,37 9.63° o'm=11.5° 1971. 1970 528 2563 .43 7.40° 0'm=11.6° (9) KENNEY, T. C. An examination of methods for calculating slope stability. M. Sc. * Two alternative toe positions have been taken: (a) passes along the old slip surface Thesis, Imperial College of Science and of the 1883 slip, and (b) passes through the landslide debris. The most critical was Technology, 1 956. Traditional found to be (a). 0 'r along old slip surface assumed to be 11 °. 24 living corridor (10) MORGENSTERN. N. R. and PRICE, V. E. ** Taken as acting at a uniform inclination to the horizontal and evaluated in terms of The analysis of the stability of general slip total stresses. surfaces. Geotechnique. 15 (1), pp. 79-93, *** Obviously, the mobilized angle of shearing resistance 0'm is equal to the residual 1965. Articulated corridor with angle if the factor of safety is unity. (11) HUTCHINSON. J. N. and BHANDARI, An example of cluster development Some dwelling integration possibilities individual entrances Note 1: With residual strengths along AB : C'peak=0 and T= 1 675, an'=4600 along BD, R. K. Undrained loading, a fundamental however, with residual strengths along AC: C peak = 450 with T=1200.

i clearly show how the blocks of apartments This article appears in Tubular Structures field operations in the autumn of 1 968 in all were to be articulated and varied in order to no. 21 and is reproduced here with the regions except the Eastern States, where access to the sites was not possible until early turnet J be totally integrated into many different editor's permission. 7&L m situations. 1970. Due to the requirements of the main contract programme, however, the tower 1 The drawings were prepared by Bryan Introduction designs for fabrication tenders had to be 7 A 5 living HUM Seymour and David Lay. The microwave radio towers described in this article form part of a contract for the provision based on provisional heights. of a microwave radio relay system for Step III The final tower heights and orientations —i became available, route by route, at intervals, 2 livini rooms of the Nigerian National Telecommunications n + servicserv« e inse' Development Plan. The main contract, one of as information was received from the survey teams during the first few months of the • the largest of its kind ever placed with a \ currency of the fabrication programme. Design British company, was awarded to The Round members General Electric Company Ltd. in 1968 and, details were then issued to the fabricator in batches according to a predetermined Dwelling arrangements Each variant can be to the opposite hand in addition to the radio equipment, comprises the supply and installation of aerial supporting sequence. The tower design philosophy structures, aerial systems, power supply adopted to deal with these circumstances is equipment, equipment buildings and all described later in this article. Balcony variation : , ___ associated civil works. Tower design specification The main contract specification called for 0 C 4 living 0 0-2 0-E • oom- 0 2 * living roomi 1 Ii vine roo IT O.J bakonbalconyi variation 8 bed si The Step III microwave and VHF radio relay self-supporting towers at the terminal stations Q ? 3 living rooms system utilizes 93 entirely new stations, as Fig. 2 Solidity ratio this variation can be used on the network, but allowed consideration of with other dwelling : well as the refurbishment of existing facilities guyed masts for the intermediate, or repeater Drag coefficients for latticed towers , f J and the addition of updated aerial systems at stations. In view of the wide range of tower f some link stations, to provide a network heights and the variety of aerial arrangements • - covering nearly 4000 route kilometres. The proposed, however, and coupled with the For the consideration of tower rigidity, new system will be integrated with existing the operational design requirements were :: limited site area available at a number of the transmission systems and telephone exchanges stations, it was finally decided to provide expressed in terms of displacement of the in Nigeria, many of which, including the self-supporting towers throughout. aerial mounting point in azimuth and elevation, 760 km. Step I network, were also provided The specification also required that the taking account of the relative displacements by The General Electric Company Ltd. When supporting structures be designed with of the aerial with respect to the supporting completed towards the end of 1 972, the sufficient strength and rigidity to permit structure, such that the resulting radio beam network will connect all the large centres of displacements would not exceed the half- ••• system operation without noticeable trans• : population in Nigeria, as well as many smaller mission degradation under the action of wind power points at the specified design wind communities, to give the entire country an velocities. J velocities of 38m/s for structures located advanced telephone service. The nationwide north of the Niger and Benue Rivers and Two types of microwave equipment are used f t extent of the system is indicated by the map 33.5 m/s for structures located south of these in the system with transmission frequencies $H 3 living room: roorr in Fig. 1. which also gives the transmission 8.i t» rivers. In each case the design wind gust of 6 GHz and 2 GHz, both utilizing 3.65m frequencies adopted on the various routes of velocities were defined at 10m above ground diameter GEC parabolic dish aerials, in : the network. level, and were assumed to vary with height addition to Yagi type aerials for VHF trans• 5 * The Step III contract is a 'turnkey' project in according to a power law profile. missions. The specified radiated beam

8.S I8."4 8 which The GEC is responsible for all aspects displacement requirements were as follows:

Fig. 8 f . 8.3 Dwelling arrangements 8.1 8.4 8.4 Fig.1 Aerial frequency Total radio beam Tower Nigeria Step route map

6GHz ±0.55° 0.45° NIGER 2 GHz ±1.30° 1.20° SOK0TO r VHF ±10° 10° M8- L14s L14<

GUSAU Wind loading The resulting wind forces acting on the tower body structure were obtained using composite drag coefficients consistent with the plan shape and the type and arrangement of members used in the construction. The drag See 8. BUSSA coefficients used in the design exercises were LA LA expressed in terms of solidity ratio ; the ratio of area of exposed steelwork to envelope area of NIG/ERIA that portion of windward tower face under consideration (Fig. 2). The effect of angle of incidence of the wind to a tower face was LSI L10; allowed for by means of amplification factors, HI* * L0K0J again expressed in terms of solidity ratio, y ) / t^^i^SMUliBU »*** MAKURDI applied to the calculated drag coefficients. The wind forces produced by the aerial arrays See 8.2 ! CAMEROON were determined from wind tunnel measure• See 8.1 DGOJA ments supplied by the manufacturers, and the ENIN CITY ENUGU >»*••.. forces acting on individual structural members, ABAC AMI" The Nigerian National Telecommunications Plan Step 3 : ONITSHA/V., 6 GHz broadband radio systems ladders and feeder cables, etc., were assessed SAFE Li 2 GHz broadband radio systems using published values of lift and drag •UMUAHIA; 450 MHz narrowband radio systems .12circuit open wire line systems coefficients for isolated members. Fig. 9 ------VHP narrowband radn systems Choice of tubular towers IIXXKX 6 GHz equipment in service (step 11 Area co-ordination HARCOURT +•••••• 2GH, equipment in service The decision to use tubular steel members for for typical dwelling the construction of the towers was reached GEC-AEI Telecommunications Ltd at the pre-tender stage of the main contract. 1C A solution MSa With the available time and resources the -I r dwellings had to be standardized, and whenever possible, system and industrialised A1 i.57n building methods would be used. This O A2 1.57m standardization however, had to be capable :: : - > B1 6 10m of producing variety and not the usual monotonous rows of repetitive blocks. 305(1 1 B2 7 62m The first set of illustrations in Fig. 1 shows simply how three types of dwelling; an o !(£m B3 M1*3»Sr» Y1 3*» apartment, a single storey house and a two M2; mm Y2' m» storey house, can all be planned within the C 95 m Nl SO Y3 3H» same basic dimensional framework. The Yttljll? A N2 »»m Y5 T3-sii* following exercise concentrates on the Apartment 125m' 4/5 Bedrooms ¥6' 3*1m apartment form, as this comprised the vast with ample balcony space and storage N3 btm • Y7 ' 3

zones need to be used, and in the main the Section x-x subsequent plans use a double M unit. When Y»6 25n, a double M unit is used, it must be added to

the dimension of the wall zone to give Open kitchen Closed kitchen dimension L. For instance, if the standard wall-to-wall dimension M is 2.7 m and the Y19t5Sf. n n thickness is 0.2 m the wall-to-wall dimension L d " i is (twice times 2.7 plus 0.2) equal to 5.6m. It is. of course, possible to have various I J dimensions for M in any one project, but the V • 35 Mm j_ | asm | | 75 go | number of permutations rapidly escalates. ra :: The corridor spans have been restricted to Basic Heavy route Medium route Light route three basic dimensions ; the original M plus A ffff \ Kitchen Fig. 3 and B. An important feature to note is the ill _j Fittings Basic tower profiles for Heavy, Medium and Light route families facility to arrange the wall zones so that the corridor can turn a corner. The variable space either side of the service 1 It had been realized that there were certain square towers (Fig. 2). Combining these obtained from the preliminary aerial and map zone gives most of the basic flexibility, but advantages to be gained from the use of effects, it is found that the wind forces acting surveys. even here it was possible to rationalize so that tubular construction, particularly for towers on a triangular tubular tower can be as much Due to the highly competitive nature of the increase in depth of this variable space of triangular plan shape, both in terms of as 50% less than for an equivalent square international telecommunications projects, the is in steps of a sub-module. Fig. 3. area o washing machine economy and appearance. tower constructed of angle members. tower designs had to meet the contract co-ordination, illustrates the full range of areas a dining area b preparation area P. The wind forces attracted by open, latticed The wind forces attracted by the aerials, specification in the most economical manner, or parts necessary for the EVRY dwellings. variable worktops c laundry area towers composed of round tubes are however, are independent of the type of preferably on a station by station basis. At the The coding of these parts is a simple two- measurably less than for towers of similar supporting structure, and the proportion of same time, however, the designs were to be dimensional code for its size. For example a Fig. 5 Kitchen variations are made geometry composed of flat, open members. total wind force carried by individual tower sufficiently flexible to accommodate the final corridor part 'LA' is L long by A span and. Standard kitchen by adding simple worktops and space Furthermore, there is an even greater reduc• members is somewhat greater for triangular tower requirements with the least possible similarly, if s (sub-module) is 0.5m and M is tion in wind force for triangular shaped towers than for square towers. alteration of details and without delaying the 2.7, part MIOs is 2.7m span by 5.0m depth. fabrication programme. i towers compared with the more traditional The final comparison also depends on the Two particular sets of parts are shown in 1 Prefabricated - type of aerial to be supported, since there is a Solutions to satisfy these conflicting require• Fig. 9, and. from these parts, apartments 8. bathroom marked difference in rigidity between the two 8.1 and 8.2 (in Fig. 8) can be planned. The mode ic ments would have been quite simple in lifting tram types of tower. On balance, however, the final isolation. For example, the towers could have bedsitter dwelling is shown in two versions, design forces in corresponding members for been designed individually as final details one of which allows for a staircase or lift insert. ill the two tower types are similar in magnitude. became available from the survey teams, The various living patterns shown in Fig. 4. • • Taking into account the superior compression together with the kitchen and bathroom thereby providing minimum weight structures 1 protective wrap • • load-carrying properties of tubes together with within the framework of a set of consistent sheets. Figs. 5 and 6, were used to evolve •m » • the fact that there are proportionately fewer tower profiles to minimize fabrication costs. the basic grid. These living patterns show how \ Small members in the case of triangular towers, it is This procedure was not possible, however, the particular plan forms accommodate the N! • • \ Kitchen found that the weight t>f these towers is without seriously delaying the fabrication family's changing requirements. The standard substantially less than for square ones of programme. Alternatively, a complete set of kitchen in Fig. 5 is in fact only standard for 2 Basic service wall • similar dimensions. final tower designs could have been produced the complicated cabinets; the additional As a confirmatory exercise, parallel designs prior to receiving the final station details by space and worktops are uncomplicated and were developed, during the pre-tender stage basing all designs on the tallest possible tower so can be very flexible. The standard bathroom •re ItonoM flltlistl - of the main contract, for sets of towers based having the most severe aerial loading. Such a is a contained unit and only needs to be on the two types discussed. Tenders were solution would allow fabrication to proceed variable for the small dwelling when the unhindered, but would not have been internal partition is removed. This is for two obtained for both fabrication and erection, Partition economic. and comparative shipping costs established. reasons: firstly the restricted area of a small Basic removed dwelling necessitates the use of one door for small The result indicated a clear economic advan• The compromise solution finally adopted was f Bathroom dwelling tage in the use of tubular towers. to group the towers into three distinct only and, secondly, the extra space created families according to the primary aerial system provides a washing machine or laundry space. Development of standardized to be supported : 3 tower designs 29 Heavy route towers - 6 GHz microwave The need to obtain tenders for the fabrication system 3 Integrated and supply of tower and ancillary steelwork service wall Fig. 4 before final details of the structures could be 48 Medium route towers - 2 GHz microwave Fig. 6 Typical range of Medium route towers made available, meant that initial designs had' system Small kitchen and standard bathroom to be based on provisional information 1 6 Light route towers - VHF system. The need to separate the two microwave Ancillary steelwork systems arose from the radiated beam The provision of ladders, platforms and aerial Mass housing - :i:;;iju; 41 41 mounting steelwork depends on the site i! displacements specified for the aerials, and ::!::::;:::::: _n HI not from any difference in wind loading. The B3 orientation of the tower and the distribution 1 3 livingroom s 1.1 1.2 flexibility with VHF Yagi-type aerial arrays, however, offer 81 of aerial heights, both of which vary from relatively little resistance to wind and are not station to station. B3 i. r standardization subject to stringent rigidity requirements. In order, therefore, to retain the standardized These latter aerial systems are frequently tower fabrication details, and at the same carried by light guyed masts and clearly time provide a flexible arrangement of aerial Bryan Seymour indicated a different class of support structure mounting positions, all ancillary steelwork compared with the two microwave tower was designed to be clamped on to the tower Introduction families. body steel. In fact, the final locations of We have, over the last 10 years or so, become Since the distribution of aerial heights and ancillary items were generally not available • E increasingly involved in the preplanning of arrangements was fairly well established, it until after tower fabrication had commenced, our housing projects. The structural implica• was possible to develop basic tower designs so that the clamped-on principle allowed tions of modern building methods require not of standardized profile and geometry for each tower body fabrication to proceed unhindered. only our early involvement in the design family. The final overall heights of the towers Exceptions to the clamping arrangement stage, but also our full appreciation of many ranged up to about 143 m for the Heavy Tower 1 Tower 2 included the platforms and aerial mountings other problems that are not purely structural route, 123 m for the Medium route and 112m at the top of each tower, where special aerial mounting panels were provided. Also, the engineering. Apartment 1 storey house 2 storey house for the Light route. Design and fabrication Our recent exercise at EVRY serves very well were carried out in imperial units. ladder connections to the main plan bracings Fig. 5 were made permanent by introducing replace• as an illustration of some of our thoughts on Each of the three basic towers is composed Alternative arrangements of standard panels the problems of mass housing. Although most of a set of standard tower panels (Fig. 3). The ment ladder support members in lieu of the standard bracings. of the problems and solutions shown are leg members and majority of bracing members international, it must be remembered that these are Circular Hollow Sections (CHS), although The clamping details were developed with plan types were developed for a particular for economic or functional reasons some for the tower leg splices. The arrangement the fabrication subcontractor, who produced context in France. standard panels are hybridized by the part finally adopted consists of circular flange prototype connections of each type for trial The problem introduction of rolled steel angle bracings. plates welded over the ends of the tubular assembly and load testing. Fig. 1 The same basic dwelling leg, the connection being provided by a ring The new community of EVRY required 7,000 The CHS sizes utilized by the three families Tower production, supply and erection Flexibility of dwelling arrangement arranged 3 different ways of high strength bolts (Fig. 7). To ensure full dwellings and they all had to be built in a of towers range from 42.4 mm diameter for the Following the receipt of tower and aerial bearing between flange plates for the relatively short time. These dwellings ranged smallest secondary bracings to 323.9mm requirements from data obtained by the field transmission of compressive loads, the plates from one living room or bedsitters, to full diameter for the largest leg members. All survey teams, the final designs and working basic module were machined flat after welding. The splice family, six-roomed dwellings. In addition to CHS used are mild steel to BS4360 Grade 43C. details were issued in batches to the fabrica• positions within a tower panel, and the bolt this basic range of six types, each type had to *„ wall (or column) zone L Within any standard tower panel the overall tion subcontractor, who then placed final pitch circle diameters, remain constant for all be available in five grades from very simple sub module member sizes and lengths are fixed, and gusset steel orders, updated his own drawings and • 5 towers, although the number of bolts vary dwellings for the tenants with a maximum plates are identically shaped and drilled to schedules, and produced any new jigs or within a limited range according to the subsidy to luxury dwellings for owner receive any of the standard end connectors templates. Variable loading conditions. occurring within that panel. The geometry of occupiers. There were only three grades of variable s;. ji e Before commencing full fabrication produc• A simple holding-down bolt arrangement is dwelling size, the changes in fixtures and corridors each standard tower panel, therefore, remains tion of any tower family, a master tower I used to connect the tower legs to independent fittings and so forth providing the other identical throughout the range of tower containing a complete set of standard panels grades. A four-living room dwelling, for Ducts heights, thereby enabling fabrication drawings, reinforced concrete foundations. To avoid the 2 and all types of ancillary steelwork, was trial example, was available at 77. 82 and 86 m . Service problems of non-standard detailing and templating and jig production to proceed assembled at the fabricator's works in It is difficult to relate this directly to our own zone templating in the base panel of each tower, span A Corridor ahead of the release of final working details - Hereford (Fig. 9). housing standards as we rate a dwelling by > one set of standard panels being sufficient for the lowest leg splice in each panel was raised Due to the programme requirements it was the number of bed spaces and not living Stairs all towers in the family. sufficiently to receive a standard base Lift not possible to check assemble the setting-out rooms. Also there is the problem of service Fig. 4 shows a typical range of towers from connector for attachment to the holding-down B templates for the foundations against the ducts and stores and similar spaces, either the Medium route family. bolts (Fig. 8). corresponding tower base panels. These being part of, or in addition to, the basic area. spanB Member loading variations within a given The use of standard details in this manner templates were fully triangulated, however, The actual dwelling areas were only part of a standard panel, due to differences in design, allowed all the tower body steelwork to be and all connections were made with close whole series of areas that included nett and B windspeed or the number and arrangement of described by a set of tower panel drawings, == tolerance bolts. Each template was assembled gross area ratios for access and service aerials, are catered for as far as possible by with schedules listing the appropriate tubular BF before issue and checked by tape measure• facilities; also, the dwelling densities varied making use of the further advantage of wall thicknesses, end connections or splice ment, the accuracy achieved by the fabricator in different parts of the project. spanM tubular construction, namely the range of types for each tower. being better than 0.02% in overall length. The majority of dwellings for EVRY were to 31 different wall thicknesses associated with Tower and ancillary steelwork followed the be provided as single-level apartments in each tube diameter. This exercise shows the inter-relationship delivery of foundation holding-down steel• various types of block with internal corridor Fig. 2 access. These blocks would vary from low of space and structural zones. Extreme variations of loading beyond the work and setting-out templates, according to Basic planning grid The actual sizes are irrelevant in an overall sense walk-ups to high-rise point blocks. capacity range of the standard member size, a sequence to suit the tower erection To set the background to this planning resulting from severe aerial configurations, are programme. exercise, the following summary embodies accommodated by a more appropriate arrange• [ o a All steelwork was fully galvanized and treated most of the requirements that we thought LIVING m»s 114. ment of standard panels. For example, the to prevent white rust formation. Tubular o 112. flexibility. Fig. 5 illustrates different arrange• Each particular grade of apartment must be M13. 111. sealed later with special galvanized plugs. available in a variety of plan forms, with dual Ml. L14, ments of standard panels resulting in towers MIS. 115. In all, over 3000 tonnes of steelwork were M16. of identical height but having quite different aspect for the larger dwellings. These apart• 116. supplied free on board for the new towers load-carrying capabilities. For the example ments must be able to combine to form all X 6n 7. Standard gusset plate with six-bolt T-connectors under the fabrication subcontract. I 6, .(,.-> shown. Tower 1 has greater strength and possible cluster arrangements and, where Shipping of all materials was arranged by The 1 mn E industrialist, rarely realizes at the planning the location from two main points of view: Induced draft towers ion* d urt»niution noun** vow routore princtpaM Umu npraw rtaional (R.E.R.J nun stage that he wants these things - but he the effect of the location on the cooling with increased air soon remembers when he gets his tower! tower operation and the effect of the cooling entry height VftllOlW We are all very well aware that these are tower on its immediate surroundings. One only See Fig. 4 : conflicting requirements, and their interpreta• Effects of location on tower operation Forced draft counterflow tion, their achievement by careful evaluation It is necessary to evaluate the likely effects on Half of induced draft and compromise, is often left in the wrong i the following parameters essential to cooling counterflow mm hands. LMAY MtllCI tower thermal performance: None: a pit Provided space permits, a Responsibilities (a) Free access for entering air sunken induced draft r AJML B4 Perhaps we should examine the responsibili• counterflow tower with .MM; (b) Danger of recirculation of outlet air to inlet ties of the various involvements. horizontal air inlet baffles Mini (c) Uplift in air wet bulb temperature It is the responsibility of the designers of the at deck level, and discharge inn (d) Air (and hence water) contamination Jill! site, and of the plant which it serves, to air bonnets or cones i ii i ensure that the cooling tower installed is (e) Spoiling of fan performance (Fig. 5).

1 i' suitable for its job in terms of its performance, (f) Access for erection and maintenance Sunken crossflow or U Uff III application, location and appearance. due to the positioning of the tower in forced draft liable to 111111 nun The prime responsibility of the manufacturer relation to its surroundings. excessive recirculation .iiiniii is to provide an efficient and dependable product at a viable price, guaranteed to meet

•OISY-LE-GRAMO the performance which has been specified, and to achieve this by good engineering compromise so that a sensible balance is I i 1 obtained between the conflicting require• • ments, of which he is well aware. MISSY Si LEGER T J While there are, unfortunately, very few I cooling tower engineers, the majority of ! cooling tower suppliers (and there is a wide ! choice - perhaps three dozen in the United Kingdom) employ sales and applications staff T1GERY who are well versed in the problems and who can, when given the opportunity, provide Prtftct sound advice on the application and location of their product. But the salesman can only assess the information which he is given, and CORBEIL this rarely includes layout and planning material or sources of environmental pollution. I I I I 15km At the same time, he must come to terms with Fig.1 6 the commercial pressures imposed by a Standard induced draft counterflow and Induced draft counterflow increased air entry (b) Recirculation dangers bridge, the deck structure needed to be refined. Buildings, large items of plant, other cooling We felt especially that our sketch designs for towers and enclosing walls can all modify the the suspended spans could be improved upon. mass movement of air in such a way as to Forced draft They were based on standard systems of tort- *1 cause recirculation; indeed, the bulk of an counterflow precast beams but we thought that we could I-1 individual large tower, or bank of towers, can pair choose from a wider range as we should need B * A J have this effect on itself, and so it is clear that enough beams to make it economically viable -• the direction of the prevailing wind must be to build special shutters. We were also not w taken into account. Note that the 'prevailing entirely satisfied with the appearance of the wind' for the tower may not be the same as standard beams in this particular case. This that prevailing for the site or area. t bridge will not be seen at a distance, but «WT LOMOmCWAL SEC TON experienced mainly by those driving or ] Another text6 suggests that a tower's exposure walking under it and the shape of the soffit to wind can be taken as open if it is located at X is for that reason particularly important. Fig 5 a horizontal distance of at least 10 times the The south abutment is a long tabletop with the back legs buried in the embankment height of surrounding solid structures. Should We therefore made a special study of decks a tall building or plant item be upwind of the made up from precast beams with in situ i'' tower, the air velocity will decrease as it topping. The criteria are obviously that the precast component should be easy to make, passes the tower with a consequent tendency ^-1 to entrain the warm moist discharge back into transport and erect and that the in situ the downwind air inlet (Fig. 6). component should be easy to shutter and make. The choice of any system, however, Particular instances and partial solutions to will be greatly influenced by its ability to the problems include: distribute the effect of concentrated loads Special 4- nduced over a wide part of the cross-section. Most ii (i) Towers downstream of large buildings draft bridges in this country have to be checked when L<10H: use high velocity discharge counterflow for a load of 180 tons which is concentrated through cones. on a small area, and it is important for (ii) Banks or batteries of towers behind economy that this large load should be screen walls: mount batteries parallel to carried by a much wider part of the deck than prevailing wind, and never in series down the one on which it acts. Our study resulted wind (Fig. 7). Provide fully louvred enclosing in a precast trough unit with an in situ slab walls with ample free area for entering air. on top. It compared well with standard Use only high velocity discharge, preferably systems in our cost estimates and we thought with cones or bonnets. In some instances, a that its advantages, particularly in construc• cure may be achieved by fitting decks or tion, might well in the end make it the baffles at the top of the towers between cheaper deck. The beams can be launched from the northern end onto simple laminated Fig 6 enclosing walls and towers, also between We had a test specimen cast to confirm our design cells; this should be considered palliative and Fig. 2 rubber bearings, and they are stable and form a not as a design solution (Fig. 8). complete platform as soon as they are placed, which is important over the railway. (iii) Single entry crossflow towers should be There is no prestressing to be done on site installed sideways - on to the prevailing wind and the reinforcement in the top slab is very (or modified wind direction due to surround• simple. Shuttering is not needed between ing structures) during critical performance the beams and easily supported over them. periods. Large baffles fitted to top of tower There are no transverse beams except at the can ameliorate recirculation, but again, this is ends, where they are easily cast, but the final not a design feature, merely a solution to a structure is nevertheless very good at problem (Fig. 9). Single entry crossflow distributing loads transversely because of the towers are not recommended for use on high torsional stiffness of the boxes. critical design duties because of the orienta• I- 3 We produced a very refined design for the tion problems. L trough units as they are to be cast under factory (iv) Induced draft crossflow towers have conditions and because each superfluous bit I I high air velocities at the upper sections of of material would be repeated 84 times. To inlet air louvres, and a pressure pattern is make sure that the thin webs could be created which can encourage recirculation n concreted without problems we had a test (Fig. 10). For this reason, extended discharge made. We had a 3m long specimen cast cones are normally fitted to these towers, and • complete with reinforcement and the cable are frequently designed as pressure recovery ducts in their worst position. The test stacks thus aiding fan performance. Single entry crossflow Double entry induced draft crossflow confirmed our design and we shall be able • to provide tenderers with more information (v) Buried, or partially buried, counterflow as well as be able to answerquestions with the induced draft towers exhibit similar effects to confidence that results from having cast one the induced draft crossflow tower. Again, already. The test also gave us a chance for a extended discharge cones should be fitted, preview of the concrete surface that we are together with decks or baffles, at the top of planning. the tower and there should be ample air entry M at the tower base. We studied many complicated structures for l the tabletops. but chose in the end a solid (vi) Forced draft counterflow towers have reinforced slab. A solution for the abutments Fig. 7 lower air leaving velocities so that contributory practically presented itself. The junction Some of the structures for the suspended spans that were compared. factors increase the recirculation risks. Choice between earth embankment and structure is The three upper structures are based on standard precast beams; of location is again very important. Therefore very important, but often difficult to design. the lower is the design that was chosen. Precast beams are shown shaded. the fitting of extended discharge bonnets and Here we could make the tabletops longer and top decks may be of assistance (Fig. 11). bury the hind legs in the embankments. The Ample free air entry area is essential at low trough units need not be adiusted here and level. Forced draft towers with opposed fans all precast beams can be made identical. operated on sequential thermostatic control We presented the scheme to the Royal Fine are subject to recirculation unless fitted with Art Commission in November 1971 and are flow reversal dampers. now (May 1 972) in the final stages of design. Provided that the dangers of recirculation are We have estimated the cost of the project to -u w \J w w vl 2 made known to the tower supplier, he may be be £745.000 or £93 per m . The viaduct is —— . « . able to make allowances for the condition in only a small part of the whole contract which his selection. This will normally result in a i i i i covers the North Orbital Road between SCCTIOM A - A in™- , , . i— MCTMH I • I larger, more costly tower, or increased fan Hunton Bridge and Maple Cross. The horse power, or a combination of both. Hertfordshire County Council Sub Unit of the Fig 8 Addition of discharge bonnets and higher fan Induced draft counterflow increased air entry Forced draft counterflow back to back Eastern Road Construction Unit are designing Cross-sections. The suspended spans (to the left) are partly precast, stacks (cones) can sometimes reduce fan the rest of the works. We hope that tenders the tabletops (to the right) are cast in situ. horse power due to the gain in 'stack effect' will be invited in late autumn; work should 20 but these gains will be marginal. Fig. 3 start on site early next year and last two years. It is suggested that any space and cost be used in circuits containing copper con• penalties, avoided by not taking precautionary denser tubes. measures against recirculation, will be more The general solutions and precautions to be ^ I 1 than offset by the increased costs and taken include: C3 o embarrassment caused by subsequent lack of H 21 \ thermal performance and remedial action (i) A careful study of the proposed location in relation to both the plant or building which ,:i \ \ which will have to be taken. the tower is to serve, and also a survey of i (c) Uplift in air wet bulb temperature possible sources of trouble in the surrounding UJ 9 sl The dependence of the water cooling tower area. upon the wet bulb temperature of the entering O O air is well-known. What is not so often (ii) Consideration of the use of air inlet filters appreciated is the severe penalty on thermal (these must be regularly cleaned or water will q i performance which results from incorrect be held up within the tower). In heavily air - selection of this leading design parameter in contaminated areas, such as steel works, the • I a 2 : terms of the effects of surrounding features, use of bypass water filters may be advisable. 1 1 • M i \ 1 6 M.I 1 Li both natural and man-made. Other texts , (iii) In areas of heavy environmental pollution, 7 should be studied for detailed information, consideration of the use of closed circuit ; since space permits only brief comment here. i cooling water circuits using either air blast Forced draft Half an induced draft 1 :: i Situations in which the wet bulb will be ! (fin fan) coolers with subsidiary sprays under counterflow crossflow i M l 07 increased include the following : elevated ambient air temperatures, or alterna• • • 5 tively closed circuit coils within a cooling (i) Recirculation: Kunesch in his recent Fig. 4 tower concept, making the necessary detailed paper quotes numerical examples which studies. o indicate the seriousness of this problem. z (iv) Planning for effective water treatment items is a near certainty. The results can vary o (ii) Air discharge grilles from building air O and regular blowdown, as necessary. The from distasteful nuisance to actual damage, ! o o conditioning, process steam discharges and advice of a recognized water treatment including : effluxes from other cooling towers, from hotel specialist should be obtained. Mixtures of (i) Staining of buildings, including salt o bathrooms, laundries and so on, can adversely metals in construction should be carefully 1 deposition and biological growths 9 a . .H20 O affect cooling tower thermal performance by studied and incompatible mixtures avoided - no elevating the entering wet bulb temperature. water treatment is not a panacea in such cases. (ii) Corrosion of metal surfaces (iii) Etching of glazing. (iii) Close presence of dense vegetation, (e) Reduction in fan performance SITE PLAN particularly if the tower is surrounded by damp The effect of altitude on air pressure must be Use of lower water loadings (larger tower plan natural growths. taken into account in the determination of fan area and greater vapour dispersal) use of performance. extended fan cones to carry the nuisance past Certain advantageous situations can arise in the surfaces and also tilting the fans away from which the wet bulb is reduced : •j.'.r 5 Restriction of air inlets, dirty air inlet louvres critical areas, have all proved effective. or filters, dirty or maladjusted packing and (i) Wet bulb reduces with altitude : the correc• (b) Downwind vapour drift 1 6 water distribution, blocked or dirty eliminator tion suggested for the British Isles ' is about Even when condensation on critical surfaces 0.5°C per 100 m of elevation. sections, and restriction of air discharge, n all adversely affect the cooling tower is avoided, the warm moist air stream will (ii) The presence, upwind, of large stretches performance. condense, at periods of critical dewpoint, into of water actually can have the effect of a cloud of vapour which can persist for All the relevant factors previously discussed lowering the incident wet bulb. considerable distances downwind. In really should be taken into account in order to difficult situations, such as near aircraft run• If the cooling tower supplier .is aware of the reduce these effects - in particular the ways, gas burners have been installed within sources of possible influence on wet bulb proposed location should be studied for the fan discharge stack - but the cost of their temperature in the neighbourhood of the site, secondary obstructions to air flow such as use is very high. Fine nylon mesh screens arrangements can be made to take these into beams, cills, parapets, and items of equipment SOFFIT PLAN have proved effective in one instance known account in the design and selection of the which may not be installed according to plan. to the author, by causing a percentage of the tower. In particular, structural members such as moisture to condense above the tower. beams can create serious vibration problems (d) Contamination of air and water by disturbing the flow of air over the leading (c) Windage and carryover Tower performance can be adversely affected edges of the fan blades. At times of high wind, water may be blown by entrainment of foreign matter of various out of the bottom of towers unless crosswind 12 5 II10 S2 0 3?0 31'I) !;•() .120 types. It has to be remembered that the cooling (f) Access for erection and maintenance baffles are fitted. This is a frequent cause of

40 4-0 tower is a highly efficient air washer: The proposed location should be studied to icing of nearby paths and roads in winter, ensure that the supplier can indeed erect the when the tower is situated too close to such n (i) Entrainment of fumes from boiler flues r tower, and that the essential normal mainten• routes. It is recommended that a distance of will reduce the pH of the circulating water, ance is possible, with a sufficiently large drain some 6-9 m should be allowed between large 3H! :: •r resulting in rapid deterioration of the piping, to carry both water and sludge, and a cooling towers and roads, according to the a- heat exchangers and the tower itself, due to convenient hose connection to make washing height of the air inlets, because the effective• CM corrosion. down possible during draining. The functional ness of crosswind baffles varies. design features of the water storage basin are 3H1 • (ii) Other processes and effluxes, particularly of prime importance in the ability of the system -E3- oil and diesel fumes, will affect performance to operate consistently and correctly. by coating the system with greasy deposits. Entrainment of cement dust from adjacent FOUNDATION PLAN Effect of tower on its surroundings c building operations is a common source of It is advisable to study the results of the trouble. following effects which may create problems (iii) Contamination by entrainment from within the immediate surroundings of the biological sources such as kitchens and tower: bakeries, laundries, paint spray booths and (a) Condensation of moist air discharge printing processes, will result in organic (b) Downwind vapour drift growths which will attack both the system r and the tower itself. Failure to apply remedial (c) Windage and carryover (d) Noise from fans and water 80 action could result in total blockage and structural collapse of the tower internals. (e) Weight of tower and water i ' 25 (f) Results of accidental leakage i1 (iv) Similar effects can result from blockage by leaves, catkins, bird feathers and droppings. (g) Appearance in relation to surroundings. • 0 Metropolitan Line Berry Lane The high velocity intakes to forced draft fans In all cases, the best solution is to select a are particularly prone to picking up rubbish, location which avoids these problems but. v SECTION C - C leaves and sheets of plastic film. when this is not possible, other measures must be investigated. (v) Contamination of the water can also arise from mixtures of metals in the cooling water (a) Condensation of moist air discharge circuit, resulting in products of corrosion and Since the discharge air is to all intents nearly Fig. 5 Fig 4 in metals dissolving into the water and thus 100% saturated with moisture, at a temperature Sunken induced draft Site plan, soffit plan, foundation plan, section C-C. accelerating corrosive action. In particular, above that of surrounding surfaces, condensa• counterfoil air inlets horizontal 4 zinc (galvanizing) and aluminium should not tion on nearby walls, windows and plant Droplets of moisture can be tossed from the rails can only be carried out at night and then Huntonbr d g* tops of high discharge velocity towers even only for three hours at a time and there are Ml when eliminators are fitted. The combination restrictions on the methods of construction that the railway authorities will allow. of concentrated impurities in the water and Strati sunshine will mark the paint finishes on Having identified these main considerations Latimw motorcars and plant. Unless the air discharge we were soon able to establish some general velocity is low, and very effective eliminators principles. It seemed right that a simple are fitted, towers should not be located close repetitive structure should be used ; we could see no reason to single out either Berry Lane to car parks and roadways used by the LaTimar Sta WATFORD general public. or the railway and make larger spans over them and we found in our cost estimates that : (d) Fan and water noise the economic range of spans in any case is ClKr lay weed o0(S This subject and its problems and solutions, larger than both these spans. The conditions urr.moi 1 3 Ml are dealt with in some detail in other texts , . for prefabrication are obviously favourable Cro.lay WortWd It is sufficient here to emphasize the highly and we thought it would be useful to use a O.h.y BUSHEY emotional response evoked by unacceptable split structure with separate decks for each HTl Or

noise levels and to make the following carriageway. This should give some advan• BERRY LANE VIADUCT ICKMANSWORTH Fig. 6 reminders: Fig. 9 tages in construction but, more important, we

L <10H increases recirculation Single entry crossflow could make a gap in the wide slab which Moor Para (i) Running a fan continuously at part-speed would otherwise blot out the sky over the Mapl at night is more acceptable than cycling it on f whole width of the road. This, we hoped, C and off. would help the vegetation under the bridge Chalfont Common (ii) Quiet cooling tower performance can be in establishing itself again as some light and rain would pass through the gap. o o o o o achieved using slow-speed or quiet running North*, tod o o 0 o o centrifugal fans and motors if the supplier At this stage we prepared sketch designs of knows of the problem at planning stage. Also, some structures which all fulfilled the require• Horoli .id -i 'on! HMtfflOM L both inlet and outlet silencers are available as ments mentioned so far. They range from St Mor standard accessories on some makes of tower. continuous girders to tabletop structures with precast beams suspended between in situ 0 (iii) Fan cooled motors are more than tabletops. We considered different cross- ordinarily noisy and should not be used. sections and materials and compared the 6ar rare* (iv) Tower water noise is real, but can be schemes on their functional, technical, r c ; i North Harrow modified by use of anti-splash decks in the economic and aesthetic merits. In the end we o o o o o surface of the water basin. This should be at chose a tabletop structure. This structure the operating water level which will be below compared well with the rest on all counts o o 0 o o the level of the surface when the tower is not and we thought it was superior in one Fig 2 Fig 3 below in use. respect; each tabletop was supported by four The whole contract covers the North Orbital The mam access should be from the north very slender columns which could be made Road between Hunton Bridge and Maple along the cutting for the future road where it (v) Towers should not be mounted in noise- nearly as thin as the trees that surround them. Cross. is wide to provide for sliproads. sensitive courtyards since reflection increases Other structures were supported by two the noise level by up to 1 5db. columns which were necessarily much Fig. 10 thicker. We compared these two column Prevailing Wind (vi) Fan/motor/gearbox noise can be trans• Crossflow induced draft mitted through the structure of the plant and types in simple models and found the thicker building, and the usual precautions taken for columns much more conspicuous although o o o o o moving plant items apply also to cooling only half the number was used. As mentioned 11 o o o o o towers. Ask, what is situated below the before, the trees tend to hide the supports if The construction of the tabletop structure is cooling tower? ! t ! they are slender enough. We also found that well suited to this site. The smaller part of the the relationship between the four columns is structure is cast in situ; it is reinforced only, \2 (e) Weight of tower and water PT7 important; they should be close enough not prestressed, and we have made the It is not always recognized that the operating together to read as a group and not just appear members bulky so that the concrete can be I Fig. 7 1f t I V Orientation of multiple tower weight of a cooling tower is high, that the as a forest, but they should not be so close easily placed. Each tabletop is stable at all banks, D to be < L quantity of water held within the packing and • 1 J that the light and diffuse character is lost. stages during its construction and it provides contained within the storage basin of even a Tabletop structures form a clear and simple a platform from which to place the precast MS *^ packaged tower may well equal the weight of f structural system and this perhaps adds to beams. These can be brought in from one end. the tower itself. Suffice to say that the their appearance. It is easy to see how the There are no bearings or complicated joints f ii^.r™ foundations or structure beneath the tower structure carries its load and how it is within the in situ work to slow up construction must be capable of carrying the weight of constructed. All the precast spans rest simply and scaffolding can easily be erected on top VIADUCT tower plus water! supported on the tabletops and each tabletop of the footings. We thought at first that it RESTRICTED ACCESS is in itself a stable structure which carries all would be a good idea to save some of the • (f) Accidental leakage loads that act on it, including bending and scaffolding and we studied a scheme for Once again, ask, what is underneath the horizontal loads, to its foundation. We chose casting the tabletops at ground level and ,J-4 .: tower ? to make the tabletops comparatively short then jacking them up on the columns. This V ICI'H The design of the piping circuit between the 1 and to support the suspended spans on produced no savings and it introduced an hinges at both ends in order to limit the awkward joint to be made when the tabletop cooling tower and the plant which it serves RESTRICTED ACCESS should be studied to determine the quantity bending that has to be carried to the had reached the top, so we gave up the idea. of water which will drain down into the tower foundations. Having taken the fundamental decisions about basin when the pumps stop. Can the basin Fig. 11 the structural system and how to build the accept this water without waste through Forced draft overflowing ? Draining of the heat exchangers in the plant should not be permitted since other operating difficulties arise as a result. Fire precautions Extent.on (g) Appearance Con* It is not always recognized that a cooling The engineer, as well as the architect, should tower is a very real fire risk. There are many be concerned about the appearance of the cases of destruction during the plant construc• tower, both when new, and also after some tion phase, from welding sparks or due to a years of operation with minimum maintenance. casually dropped match or cigarette. A timber Perforate Quite often the architect does not appreciate Screen tower which has dried out during a period of Wall how large a cooling tower can be, nor that maintenance is easily set alight - and the there is such a wide choice of types, arrange• natural draft effect quickly fans the flames. ments and finishes. There is full scope at the In and on buildings, sprinkling or drenching planning stage, but very little by the time the engineer is finalizing the details. of the outer casings may be advisable. In general, it is common sense not to allow a There are many examples of towers totally timber packing to dry out completely. unsuitable for their surroundings, which While there is still no standard for fire become an eyesore and a sad monument to precautions in respect of cooling towers in the Fig. 8 the lack of care, understanding and interest United Kingdom, the National Fire Protection Towers installed of the building designers and site planners. Association in the USA publishes NFPA behind screen walls Nobody's baby grows up with a very sore Standard No. 214 which is a useful basis for thumb! study of underlying principles. Vol.7 No. 3 September 1972 Contents Appendix 1 - Application checklist (ii) The location, i.e. whether at ground level, materials (study mixtures of metals due to Published by Ove Arup Partnership 1 Select as first choice the best possible on or within a building. other equipment). THEARUP 13 Fitzroy Street. London. W1 P 6BQ position, checking for: (iii) A guide to surrounding environment, When the tower is to be installed in the open, (a) Effect on tower e.g. built-up areas, woodland, harbour, etc., the enquiry should state whether ancillary items such as immersion heaters, ball valves, Editor: Peter Hoggett Free access for entering air, ample perforation which may affect performance or selection of Art Editor: Desmond Wyeth FSIA Recirculation danger (L< 10H), need fordecks materials. Adjacent railways, process effluxes, strainers, fan guards, cover, thermostats and JOURNAL Editorial Assistant: David Brown Prevailing wind, orientation of tower batteries and industrial chimneys should be mentioned. motor starters are to be- included in the quotation. The Berry Lane Viaduct, 2 Air contamination ; other plant items, effluxes, 3 Limitations by J. Nissen filters Are there any restrictions in height, plan area, 5 Services Uplift in air wet bulb or access for erection which may affect the The enquiry should state the volts, phase, The Evry 1 Competition, 6 Spoiling of fan performance due to position type of tower offered ? Is there a preference cycles of the electricity supply, and should, if possible, give the source of the make-up by M. Barclay of tower in its surroundings for a particular type, e.g. induced draught (low plan area), forced draught (limited air access), water if this is other than town mains supply, The need for fire precautions e.g. artesian well. lake, river. Mass housing - 8 cross draught (height limitation) should be flexibility with standardization, (b) Effect of tower stated. Bibliography by B. Seymour Condensation of moist air discharge; cones Specify also: and bonnets (1) GURNEY, J. D.andCOTTER, I.A. Cooling Limitations due to noise (adjacent residential towers. McLaren & Sons Ltd., 1966. Now A study of a large landslide 12 Downwind vapour nuisance areas at each side or below) available from Applied Science Publishers Ltd. at Heme Bay, Kent, Windage and carryover nuisance Limitations on carryover due. for instance, to by E. Bromhead Noise from fans and water; silencers, part- (2) INSTITUTION OF HEATING AND windows adjacent to discharge VENTILATING ENGINEERS. IHVE Guide speed motors, anti-splash decks, anti-vibration Tubular steel microwave 15 Limitations in working weight due to structural 1965. Section J 5c. IHVE Guide Book, insulation towers for Nigeria, considerations for a roof-mounted tower Volume B. 1970. by M. Shears Weight of tower and water Restricted access for air inlets, and dangers (3) GOLDBERG. N. Control of noise of Dangers from accidental leakage of recirculation. cooling towers. Air Conditioning, Heating and Planning to avoid cooling 19 Appearance and visual suitability. Ventilating. 60 (6), pp. 58-61. 1 963. tower misapplication problems 4 Construction (4) JONES. R. S. Misapplication and incor• by D. Gurney 2 Evaluate any problems and compare alter• The enquiry should state: native locations. rect location of cooling towers. A paper read Whether the casing is to be of before the Cooling Tower Institute. 16-18 3 Examine alternative types, arrangements (a) manufacturer's supply June. 1969. and finishes of tower. (b) builder's work supply Front cover: The Berry Lane Viaduct. (Photo: David Faggetter) (5) KUNESCH, A. M. Relative merits of 4 Provide maximum useful information to Whether the basin is to be of combining natural and mechanical draft Back Cover: Computer drawing of Nigerian radio tower potential suppliers - see checklist for (a) manufacturer's supply cooling towers. A paper read before the specification to suppliers. (b) builder's work supply Cooling Water Association in London on 25 February, 1972 tunnel would have had to be artificially lit attractive than others. Berry Lane passes Appendix 2 — Checklist for specification If (a) in either case, a statement of materials (6) EVALUATED weather data for cooling The Berry Lane 24 hours a day. through narrow tunnels on both sides of the to suppliers should be requested, or specified, in the equipment design. Head Wrightson Processes Our main task was easy to formulate: we site so that only light traffic could pass this 1 Performance - specify: enquiry, as should a description of ancillary fittings such as drains, purge connection, Ltd., London, 1963. Viaduct should design a structure which would not way. The main access should therefore be (i) The water flow rate from the north along the cutting for the future make-up valve, etc. act as a barrier and which would preserve the (ii) The inlet and outlet water temperatures Acknowledgements character of the woods as much as possible. road where it is wide to provide for sliproads. If (b), the enquiry should specify cover for Jorgen Nissen (iii) As a check, the heat to be removed The author is grateful for very real help and It was more difficult to see how this could be This cutting will, of course, not be available supply of all necessary drawings to enable the encouragement from friends and colleagues The Berry Lane Viaduct will carry the London done. A 35 m wide slab suspended some 1 8 m at the beginning of the contract and the (iv) The design ambient wet bulb temperature contractor to construct the casing and/or who have offered advice and guidance, North Orbital Trunk Road over a deep valley above ground is an imposing feature which foundations will, therefore, most likely have (v) Altitude of site basin, including the necessary baffles, filters quoted examples and made pictorial material to be constructed from Berry Lane. Fortunately, in Chorleywood. A small country road called cannot be hidden away, but in this case the 2 Location - give: and drains to trap and remove sludge. available: among these are A. M. Kunesch, they can be made as simple footings as we Berry Lane runs along the bottom of the valley woods seemed to help us. Inside the woods (i) The area or town in which the site is Preference for any material, e.g. type of E. LeMay, J. R. Neller, D. P. Rayfield, K. Rogers found firm chalk below a very thin layer of and the Metropolitan railway runs on the there are no long views along the valley; the located packing, should be stated. Restrictions in and G. Slaughter. south slope. The valley is full of trees and trees stand in the way, and the ground is alluvium over most of the area. very pleasant and much used by walkers. It is mostly in the shade of the trees. The trees are The structure should also be suited for a residential area and private houses lie in the same height as the viaduct and we felt construction over Berry Lane and. more the woods. that we might soften the impact of the important, the railway. This is very busy as it carries the Metropolitan underground trains The North Orbital Road is being designed by structure if we could design a light and as well as trains for British Rail. Work over the the Department of the Environment, but in unobtrusive support structure of the same April 1 971 we were asked to prepare a design scale as the tree trunks. We would, so to for the viaduct. It was only natural that our speak, try to keep the feel of the wood under clients should stress the importance of the the bridge. To succeed in this, it would be environmental aspects in their brief as these very important that the woods should be were the raison d'etre for the structure. An disturbed as little as possible during construc• Fig 1 below tion and that their natural character could embankment had earlier been considered ; it In designing this bridge, we were determined easily be restored in the areas that were would have been some 18m high and around to preserve the woods through which it disturbed, so that a scar would not be left for 100 m wide at the bottom and would com• passes, as much as possible. From this long. This limited the construction methods pletely have destroyed the woods. It would consideration followed ideas for a construc• that we could consider. also have severed the valley into two separate tion method and appearance and these Access to the site is restricted and some parts which would have been connected only principles resulted in the proposed tabletop construction methods are therefore more by a 100m long tunnel for Berry Lane. This structure. (Photo: McMasters-Christie).

Printed in England by Thompson & Tompkins Ltd. THE ARUP JOURNAL

SEPTEMBER 1972