Features of Construction

Progress, Volume XIV, Issue 3, 1 November 1918, Page 357

Features of Construction

Owing to the necessity for restricting as little as possible the space allowed for the cart area in the front of the building, it was decided to employ, in place of reinforced concrete, nine solid steel columns, varying from 6in. to Tin. in diameter, and 12ft. Sin. long. These columns were continued upwards as concrete columns. Under London County Council Regulations this arrangement would have been impossible, as the requirements of the Building Act in respect of steel-frame buildings and the Reinforced Concrete Regulations cannot be applied at the same time in any one building.

The live loads to he provided for were 401 b. per square ft. on a horizontal plane for the pitched root (including the dead load for the roof itself), 561 b. on all flat roofs, Hcwt. on the first and second floors, and 1 cwt. on the third floor. The weight of the reinforced concrete work was taken as 1501 b. per cubic ft. and of the insulating materials as 181 b. All walls were considered as subject on each side to- a uniform pressure of 40 lb. per square ft. over the whole area. The worst possible combinations of the above loadings were taken in arriving at the maximum stresses. In general the methods and formulae outlined in the second report of the R.1.8.A. Committee on reinforced concrete, dated 1911.. were adhered to.

The concrete was composed of clean crushed Thames ballast passed through a a in. and retained on a f in. screen, mixed with Ham River grit in the proportion of 2 to I, with latitude for variation when necessary so as to ensure the whole of the voids being properly filled. The cement used was in the proportion of one bag of 224 lb. to every 4| cubic ft. of sand, and complied with the requirements of the British Standard Specification, the initial set being between 50 and 90 minutes and the final set between 5 and 7 hours.

The beam moulds were so arranged that the sides were readily removed without disturbing the bottom until the beam was sufficiently set, the camber allowed for in the moulds being I MW to 3 /,,.„ of the span, according to the dimensions of the beam. The column moulds were all arranged with one open side, and this was built up as the concreting proceeded. The steel reinforcing bars were of plain circular sections, having an ultimate strength of 28 to 30 tons per square in., with an elongation of not less than 20 per cent, in Sin., and otherwise generally conformed to the British Standard Specification. These bars were covered with at least I in. of concrete in the case of beam columns, etc., and £ in. in the case of the floor slabs, except where such slabs were in contact with the insulation, when not less than 1 in. cover was provided. The minimum time allowed before removing the supports from the reinforced concrete was, in the ease of the main beams and floors, 14 days, and in the other cases 8 days. The maximum test loads to be applied to the floors and beams provided for an excess of 50 per cent, over the live load for which the particular portion of the structure was designed,

and the resulting deflection was not allowed to exceed Vfioo of the span. Refrigerating Plant The refrigeration is effected on the cold-air-cir-culation system, which in this case materially reduced the weight of the refrigerating equipment in the chambers, since the air ducts are very much lighter than direct expansion pipes or brine pipes would have been. The low temperatures are produced on the Lightfoot ammonia compression system by the expansion of anhydrous ammonia. The ammonia compressors, which are in duplicate, are horizontal, double acting, with pistons 14 in. in diameter and a stroke of 28 in., running at 55 r.p.m. and driven by 150 b.h.p. electric motors. Each unit is capable of keeping all the chambers at 10 deg. F., when the outside temperature does not exceed 75 deg. The two ammonia condensers, placed on the roof of the machinery room, each contain about 4,720 ft. of iron pipe nearly 2 in. in external diameter. The cooling water is pumped over them by two independent 4 in. electrically driven centrifugal pumps, each capable of discharging 300 gallons a minute. The aircooler batteries, also in duplicate, consist each of a series of vertical corrugated galvanised steel plates, having a total superficial area of 27,500 square ft., arranged over a wrought iron collecting tray and having above them a series of perforated steel trays, into which a constant stream of cold brine is delivered by an electrically driven centrifugal circulating pump. This pump draws the brine from wrought steel tanks below the trays, in which are placed about 5,420 ft. of ammonia direct expansion coils of 1| in. external diameter, arranged with suitable baffles to ensure efficient circulation of the brine. Air is blown by means of electrically driven propeller fans between the corrugated plates, when it loses its latent heat and thence passes through a system of air trunks into the cold chambers, returning to the batteries to be again cooled. The delivery air trunk from the batteries has a cross-section measuring 10 ft. 9 in. by 5 ft., and is contained in a reinforced concrete shaft. Six branch trunks conduct the air into the cold chambers, and six others conduct it out of them into the two return trunks. Insulation As a precaution against the possibility of moisture condensing on the insulation where it comes in contact with the concrete, the interior of all the outside walls, except that on the east side, was coated with J in. of Limmer asphalte put on in two layers. This precaution removed the risk of ice forming in the silicate cotton insulation; should such a thing happen, the value of the insulation would be seriously reduced and great expense incurred in cutting out and making good the damage, besides loss or accommodation and revenue during execution of the repairs. With certain exceptions, the whole of the insulation is of silicate cotton filled in between timber "grounds" and boarding. :V;', .For handling the produce there are two vertical continuous mutton conveyors and six goods lifts.

The conveyors, which extend from the level of the loading hank up to the top floor, are of the finger tray type, driven by 5 h.p. electric motor’s, and have a capacity of 650 carcases a minute at a speed of 100 ft. a minute. At the bottom the carcases are placed one by one on a wooden table inclined towards the conveyor, and slide down to and are retained on stationary prongs arranged to miss the fingers of the conveyor trays. From this point they are picked up by the next tray as it ascends, and after passing over the top pulleys are landed on a similar series of prongs at the upper level, thence sliding down upon another wooden table on the sorting floor.