The Works Of Messrs. Schneider And Co.

330 MESSRS. SCHNEIDER AND CO.’S WORKS. the centres of the first-course joints are 41.91 metres (137 ft. 6 in.) distant horizontally. The vertical distance between the first-course joint and the top joint is 26.74 metres (87 ft. 9 in.), The calculations for designing these three jointed trusses call for no particular notice; they wére based on the following figures : (a) Permanent Loads. Kilogrammes. Trusses, per running metre developed ... ... 160 Window purlins, per running metre ................. 30 Running purlins ... ... ... ... ... 50 Wall-plate and lower gallery per running metre of circumference : Kilogrammes. Wall-plate ... ... ... ... ... ... 80 Plate glass ... ... ... ... ... ... 50 Gallery joists ... ... ... ... ... ... 350 Total .................... 480 Covering, ceiling, rafters, per metre super ... 140 Glass and window-bar iron ai top, near the base of the campanile, per metre super ... ... 30 Campanile (frame and covering), total weight on each half truss ...................................... 2230 (b) Extra Loads. On the covering, from the lower galleries to the top, per metre super ... ... ... ... 50 On the flooring of the galleries and of the cam- panile, per metre super ... ... ... 450 (c) Force of Wind. Horizontal strain, per metre super ... ... 120 The trusses have been calculated to include : 1. Permanent loads and general extra loads. 2. ,, ,, extra loads on half trusses only. 3. ,, „ wind pressure on one side only. The limit of résistance of the steel, without deducting the rivet holes, was taken at 10 kilogrammes per square millimétré (6.35 tons per square inch), under the action of permanent and of extra loads and at 13.5 kilogrammes (8.57 tons per square inch), under the action of permanent load and of wind pressure. When the surfaces struck by the wind are in an oblique plane, the component parallel with the surfaces is not generally taken into account ; in the case of the Pavilion, owing to the redans formed by the lower gallery, the line of portholes and the Campanile with its projections, the forces of the wind usually ignored bad to be reckoned with. Therefore, the wind strains have been calculated at the rate of 120 kilo- grammes per square metre (24.5 1b. per square foot) of vertical projection of the surfaces exposed ; but, on the other hånd, the comparatively high limit of résistance of 13.5 kilogrammes per square millimétré (8.57 tons per square inch) bas been allowed for the steel. The most intricate part of the building is the common joint at the ridge of the trusses. Seen in a horizontal pro- jection (Figs. 1059 and 1060, Plate CLXIX., and Figs. 1061 and 1062), the trusses being twelve in number, the joint shows the intersection of twelve rotules, concentric one with the other and of the same diameter, which gives it the form of a bail. The bearing of the trusses on the central sphere is given by the web of the trusses and two thicknesses of plate, equal to a total thickness of 1 in. These twenty- four bearings which radiate round the summit almost toucli each other, their ends being only 100 millimétrés (3J-f in.) distant from the vertical axis of the bail, the diameter of which is 400 millimétrés (15f in.). The contact of a half truss, supposing the thrust to be horizontal, is over an arc of a circle, the chord of which is 350 millimétrés (13J in.) in length and the abscissa 100 millimétrés (3^ in.) ; or, in other words, over an arc of 120 deg. ; therefore, a radius drawn from the end of the bearing makes an angle of 60 deg. witli the horizontal. The greatest angle of thrust at the top occurs when the wind blows with the intensity of 120 kilogrammes । s ■rr—3 I553S G' (24.5 1b. per square foot). The greatest angle with the horizontal is then 32 deg. approximately, but the line still passes sufficiently far from the end of the trusses to insure a good bearing; tinder these conditions the maximum strain on the bearing surface is 3.7 kilogrammes per square millimétré (2.35 tons peu square inch). The low strain at the top permitted the sphere bearing to be made of cast iron. When this bearing is equally loaded on all sides by the trusses, uniformly surchargée!, the thrust of each half truss being of about 9400 kilogrames (say, 9 tons), it will be seen that the strain per square millimétré of diametral section is very low, being only .57 kilogrammes (.36 tons per square inch). In ordinary work, when more time can be given to érection, the purlins are fixecl only wben the trusses are in place, in order to be certain that they fill the conditions for which thoy have been designed. In this case, however, owing to the rapidity with which the building had to be completed, it was necessary to put in place the last sectors —the closing ones—and to regulate the fixing of the pur- lins, before building the campanile, and when the placing