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Aviation History
1921
1921 - 0264.PDF
"\ : :-:V:'-^v-'; country, if not in the world. It covers an area of 754 ft. by 410 ft., equal to 7-i acres or, together with the space occupied by the doors at either end, 8^ acres. " General Description.—The cross section comprises two spans, each 150 ft. by 130 ft. high, and two side portions supporting these, forming annexe workshops, each 35 ft. wide inside. The clear height at the centre of the main spans is 140 ft., and to the ridge of the roof a total of about 160 ft. Sliding doors are provided at both ends of the sheds, making four clear doorways, each 150 ft. by 130 ft. The doors are independent of the shed, and are of the semi- ballasted type, running on parallel tracks 48 ft. apart. Some details of these doors are given later. " The main spans of the shed are three-pin arches, the springing pin on the outer side, of 3 ins. diameter, resting at a height of 60 ft. from the floor on a fixed triangular framework, which forms the annexe portion ; the pin on the inner side rests on the top of the central columns, 97 ft. 6 ins. above floor. The main ribs are spaced 30 ft. centres and carry longitudinal, side, and roof girders 18 to 22 ft. apart, on which rest intermediate rafter beams, two in each 30-ft panel, so that the purlin-bars are supported every 10 ft. " The arch spans are independent of each other. Where they come together under the valley-gutter, there is a clear space of 4 ins. left and no connection is made between the main ribs except that they are held inline with each other by means of a sliding contact. Sliding joints are also arranged at each end of the piece of bottom chord under the top pin, while at the top of the ventilator there is nothing carried across except the curved corrugated-sheet covering. The arch ribs, therefore, are practically free to take up without injury any little variation in levels due to temperature or possible settlement of the foundations. A complete system of wind-bracing is provided on the bottoms of the rafters, from pin to pin, in ten of the twenty-five panels. " The annexe framework is of rigid construction, well braced on both sides of the columns, which are all connected together at the top by a braced box-girder 5 ft. by 3 ft. in cross section. At 17 ft. above the floor, cross and longitudinal girders are inserted to carry a concrete ceiling. This lower portion of the annexe framework is completely shut off from the main building with brickwork in Portland - cement mortar, the outer walls also being of brick. Cross walls occur at intervals, which divide this portion into stores, workshops, offices, &c, although at present only one annexe has been so filled in. The foundations to the annexe are of reinforced concrete, the outer blocks each having four ifj-in. anchor bolts set at an angle of 45° to resist uplift under wind pressure. " The centre portion of the shed is 97 ft. 6 ins. high. The main columns are 12 ft. wide at the top, spreading out at the foot to 30 ft., where a light steel member connects the legs together below floor level. The bottom bracing is arranged to allow of a railway track 4 ft. 8 J ins. gauge running down the centre. The columns, 30 ft. apart, are rigidly braced together with two rows of longitudinal box-girders and diagonal bars in ten panels similar to the roof portion. The foundations are reinforced, and both legs are rigidly anchored down with four ij-in. bolts. The saddles for the springing pins of the arches are built up of steel, no castings being used in the construction of the shed. " A concrete floor, with a minimum thickness of 4 inches, covers the entire area of the shed and annexes (about 34,300 sq. yds.) ; it is laid over a bed of hard core 4 ins. deep. Longi- tudinal and cross trenches are inserted in the floor as required for hydrogen mains, heating pipes, drains, etc., and mooring blocks are provided at intervals in the floor for anchoring the ships. " The ventilator framework runs the full length, having fixed galvanized louvres each side. To prevent the inlet of driving rain or snow, a small-mesh continuous wire guard is fixed outside the louvres, leaving a few inches clear space between. The sides and roof of the shed are covered with No. 20 gauge corrugated galvanized sheeting. Explosion flaps are fitted high up on each side of the main building and run the full length. These are light steel frames, 7 ft. deep, ii 10-ft. lengths, hinged at the bottom and loosely held at the APRIL 1.1, 192 r top, and covered with corrugated sheeting. Seven emergency or panic doors are provided on the ground floor, and give direct outlets without passing through the annexe workshops. Runway beams and gangways are provided as previously described. " The main roof is drained into three pressed-steel gutters $--in. and J-in. thick, which discharge direct into sixteen storage tanks, each of 5,300 gallons capacity. These tanks are situated close under the eaves-and valley-gutters, and are supported on twelve separate steel towers 120 ft. high. From the tanks, 6-in. overflow and 3-in. service pipes are led down the towers, the latter being connected up to 4-in. service pipes running longitudinally under the floor to which fire hydrants are attached at suitable intervals. The tanks are covered in and the sides and bottom are lagged, the supply pipes also being lagged as a protection against frost. To facilitate the entry of ships at night, lamps are arranged just inside the shed all round the portal frames of the doors. Gable gangways, platforms and ladders are fitted up for getting at these lights conveniently. Similar provision has also been made on the sheds previously described. The constructional material is practically all steel, but where wood is used it is coated with asbestos paint to render it less inflammable. " An observation cabin, 10 ft. by 6 ft., is erected on the ridge at one end of the shed, with access from the central gangway below, and an outside fire-escape has now been added, giving an outer gangway and ladder to the ground. Arrangements were made for covering some of the steel members inside the shed and round the portal frames with wool padding, as a protection to ships, but this was later abandoned, as were also arrangements for sliding curtains to all windows and skylights. " The site for this shed is practically level and consists of about 12 ins. of soil, overlying 6 ft. of clay, which rests on sand and warp. It was decided, under these conditions, to rest the shed on the crust of clay, and in order to avoid the possibility of penetrating it, the maximum depth of founda- tions was fixed at 3 ft. below ground level, the floor level being 6 ins. above the ground line. The depth of concrete was therefore limited to a maximum of 3 ft. 6 ins. Before fixing on the permissible load for this clay, tests were made on the site, and from the results obtained the allowable pressure per square foot was fixed at 15 cwt. " Whilst the temperature stresses in the main spans will possibly be very small transversely, the question of longi- tudinal expansion and contraction in long steel buildings usually presents a little difficulty. Assuming a maximum range of temperature in this country of 100° F., the total change in length of the shed would be nearly 5 ins., if the structure were quite free to move. But the temperature at the top of the roof will seldom be the same as that at floor level, say, and though the wind-braci«g may not prevent the upper portion expanding, expansion at the base is almost impossible. Again as the actual erection of the building might extend over a period of 12 months, it is impossible to fix on any initial temperature. " In most steel buildings it is found the bases remain fast, and in hot weather the top expands so that the ends project or lean outwards a few inches. In the present case the shed has been divided into three portions, connected together with two expansion panels. In these panels all members have slotted holes at each end, which arrangement is also found convenient for adjustment during erection. It is assumed that each end of the shed might possibly lean over about 2 ins. at the top, and due allowance for this is made in the design of the main doors. • " The question of expansion is being investigated on this shed and also on three other sheds where no provision has been made for changes due to temperature variations. Up to the present the results on two of the latter sheds indicate a longitudinal expansion of about ^ of an inch in 700 ft. for a rise of one degree in the temperature of the air in the roof of the shed. In a transverse direction the increase is about ^ of an inch in a span of 180 ft. for a rise of one degree in the temperature. These tests have, so far, only been carried out with a range of 300 of variation." Duties on Aeroplanes, Etc. FROM the Department of Overseas Trade information is now available in regard to duties leviable upon aeroplanes, aero engines, etc., on importation into various countries. Particulars cover Argentine, Australia, Austria, Belgium, Brazil, Bolivia, Bulgaria, Canada, Chile, Columbia, Czecho- Slovakia, Denmark, Dominica, Ecuador, France, Greece, Italy, Japan, Mexico, New Zealand, Norway, Nicaragua, Portugal, South Africa, Spain, Sweden, Switzerland, Turkey and U.S.A. Information upon this subject is readily given by the Department upon application. 264
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