Aluminium roofs for reservoirs and storage tanks

Two service reservoir roofs, recently completed in England for the Biggleswade Water Board, incorporate an interesting development in shallow-domed roof construction for large circular vessels. Embodying new approaches to both design and choice of material, the 125 ft. diameter 16 ton roofs are of unpainted aluminium alloy sections and sheet, and are self-supporting. An advantage of the constructional method used is that it was possible to erect both without draining water from the reservoirs.

New service reservoirs, of the type that hold supplies of filtered water for a community's immediate needs, are generally roofed over at the time of their construction to prevent pollution by airborne impurities. Older types of reservoir still in use were not covered when built, but present-day conditions make the addition of such protection more or less essential. With traditional methods of roofing, supporting columns rising from the reservoir floor are often necessary, and the reservoir must generally be drained and out of service while the roof is built. (More-over, foundations for columns in the deeper reservoirs may present difficulties, especially if the ground beneath the floor is at all suspect, and the columns themselves introduce further risk of contamination. One answer to these problems, for new or old reservoirs, is the self-supporting domed roof, and the aluminium roof represents one of the most economical types.

Built to an original design, the Biggleswade roofs are shallow spherical domes, each consisting of a grid of box-section ribs located on two series of great circles (i.e., the centre of curvature of every rib lies at the centre of the sphere of which the dome forms a small part), and are clad with flat 16 SWG aluminium alloy sheet. The ends of the ribs meet the circular ring beam, which is set in reinforced concrete, at bearing shoes with screw adjusters. Although with the great-circle-rib design the sheet panels required to cover the space between ribs are not exactly square nor of exactly the same area, it was found practical to use standard sheets equal to the largest squares, and merely to increase the overlap near the ring beam. The main ribs are of hollow section, made by riveting together two top-hat sections; intersections are made by cutting one of each pair of sections so that half of each rib runs through the joint. Joints between the 20 gt. lengths of rib are made by inserting joint filler pieces, also of top-hat section; all joints are arranged so as to be clear of intersections.

Structural sections are of Noral 51 SWP, a heat treated alloy with an ultimate tensile strength of 18 tons/sq. in., and the sheets are of Noral M57S%H alloy. It is stated that since in most conditions of normal exposure these alloys have a high natural resistance to atmospheric attack, painting or other surface protection was unnecessary. Apart from the savings in painting costs, this eliminates the difficulties associated with re-painting the inside of the roof, which would involve either emptying the reservoir or running the risk of paint falling into the water.

The roofs at Biggleswade were preceded by a 150 ft. diameter roof of similar construction weighing 23 tons over a reservoir at Eastbourne, and by other domes of smaller size. One of these, roofing a 78 ft. diameter oil tank, is interesting in that it had to be gas tight, and capable of withstanding internal working pressures of + 8 in. of water. This involved a reversal of the stresses normally applying, the dome being in tension and the thrust ring at its circumference in compression. Welding of the ribs and sheet was decided upon, instead of riveting, to ensure gas tightness, and unlike those of the Biggleswade and Eastbourne reservoir roofs, the ribs of the tank roof were single square-section hollow tubes. According to the manufacturers the basic principle of the ribbed dome of aluminium sections and sheet is not restricted to the smaller sizes of roof; a dome as large as 500 ft. in diameter could be built as successfully as one of 150 ft., using pairs of 7% in. by 6 in. top-hat sections as main ribs, spaced at 15 ft., with light 6 in. I-beams at 5 ft. spacing as secondaries. These sizes are calculated assuming that, in addition to a general loading of 30 Ib; per sq. ft., one bay of rib carries a load, due to men walking on the roof, amounting to 500 Ib. spread along 5 ft. It is also stated that insulating a roof of this kind, should it be required, is a relatively simple matter.

13. Answer the questions on the text.

1. What is the type of new reservoir roofs?

2. What is the advantage of the constructional method used?

3. What helps to overcome the difficulties of old-type roof construction?

4. What are the structural elements of this roof?

5. What are the structural and finishing materials used? What are their advantages?

6. What is peculiar in the preceded roof design?

7. What is the recommended size of the ribbed dome of aluminium sections?

14. Give your opinion on the following questions.

1. Characteristic features of roofs for reservoirs.

2. The difference in construction of new reservoir types from the old ones.

15. Speak directly about construction of roofs for water reservoirs using the following expressions:

Original design, shallow spherical, domes, series of great circles, to lie, ring beam, bearing shoes, screw adjusters, exactly square, merely to increase, the overlap near the ring be. riveting together, top-hat section, intersection.

16. Retell the text in Russian in no less than six sentences.

Unit 8

Towards Industrialized Construction

Text: Towards industrialized construction

Grammar:

· The Gerund

· The Continuous Tenses

New words:

1. access, n. [´ækses] доступ

2. achieve, v. [q´tSi:v] достигать

3. consumer, n. [kqn´sju:mq] потребитель

4. demand, n. [dı´ma:nd] спрос

5. evolve, v. [ı´vOlv] развиваться, превращаться

6. heating, n. [´hi:tıN] отопление

7. inevitable, adj. [ı´nevıt(q)bl] неизбежный

8. innovation, n. [ınq´veıS(q)n] нововведение, новшество

9. lighting, n. [´laıtıN] освещение

10. opportunity, n. [Opq´tju:nıtı] возможность, перспектива

11. prefabrication, n. [prıfqbrı´keıSn] заводское изготовление

12. productivity, n. [prOdAk´tıvıtı] производительность

13. push, v. [puS] подталкивать

14. repetitive, adj. [rı´petıtıv] повторяющийся, однообразный

15. speed up, v. [´spi:d ´Ap] ускорять

16. tool, n. [tu:l] инструмент

17. urban, adj. [E:bn] городской

18. energy conservation сохранение (экономия) энергии

1. Read the following international words. What Russian words do they associate with?

Boom, client, social, factor, standard, industry, mechanized, communication, comfort, system, computer, control, ventilation,

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