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CONSTRUCTION OF THE BUILDING.

The 72-ft trusses

'Their details ofconstruction.

The extra strong72-feet, trusses ;their details ofconstruction.

Fig. 6.

B B

Diagonals of similar width on face (B B B B B B, fig. 6) connect them, and, con-sequently, an uniform lattice-like effect is obtained. The top table of these trusses(CCC, fig. 6) consists of two pieces of angle-iron, set at the distance of an inchapart, their total sectional area equalling 3 inches. The bottom table (D D D,fig. 6) consists of two bars of wrought-iron set at a similar distance apart, andincreasing in sectional area up to 3’38 inches, as they approach the centre of thebearing. Between the angle-irons at the top and the bars at the bottom of thetruss, are passed the ends of the cast-iron standards and those of the diagonal ties;the sectional area of the principal of the latter equalling 2’75 inches. Bivets,(E E E, fig. 6,) passing through the angle-irons and bars, the standards, and the ties,connect the whole into one truss, which acts upon the principle of a rigid top tableunder compression, and a suspension-truss beneath; so pressing up the standardsor struts as to raise the centre of the upper table to a camber of 4 inches, one ofthe objects of which is to provide a sufficient fall for the roof-water. One of these48 feet trusses, complete, weighs about 13 cwt., and when, under proof, havingbeen loaded with a deadweight of 10 tons, deflected 3 inches, perfectlyrecoveringits elasticity upon the removal of the weight.

The clear width of the nave being 72 feet, it was of course imperative to con-struct a third description of truss, the depth of which should not exceed that ofthe connecting pieces generally throughout the building, namely, 3 feet, and yetsufficiently strong to support the larger weight of roof due to the increased areaof roofing it was called upon to support. The construction of this larger truss, asshown in fig. 7, corresponds in every essential particular with that of the 48-feettruss already described, with the difference that the scantling of the angle-ironsand bars is necessarily much increased, and that the total length of 72 feet isdivided into nine 8 feet lengths instead of six. The weight of one of these trussescomplete is about 35 cwts.; the sectional area of the two angle-irons (A A, fig. 7)being 5*71 inches; that of the two bottom bars, at their mtiYimnm 6-75 inches;and that of the principal diagonal ties 3'38 inches. When loaded under proof, witha dead weight of 16 tons, it deflected 6i inches, and entirely recovered its elas-ticity on the weight being removed.

A repetition of one or other of these varieties of trusses suffices to support anyportion of the flat roof of the building; but in order to carry the great extraweight thrown by the transept roof upon the last 72-feet trusses of the nave,where it intersects the transept, it was found necessary to employ trusses ofdouble depth, extra lattice-work, and much increased scantling. The construction