The Viaduct Works' Handbook

25 Tons. cwts. qrs. Iba. Plates in compression and tension bars 285 10 3 8 Angle iron in „ „ 63 5 05 Struts 77 19 3 14 Ties 44 14 2 24 Arches 7 19 0 14 Transverse girders .... 93 9 3 14 Longitudinal girders. 43 0 615 19 0 14 2 9 the side and end spans being lighter. The total weight of the superstructure is about 2700 tons, as the girders are all of excessive thickness in the centre flanges, there being six thicknesses of -inch plate for the rivets to pass through. All the holes of the main girders were therefore drilled by special machinery, which is described in another part of this book. Plate Girder Bridges, theoretically regarded as trellis gir- ders, in which the lattices are placed so close as to touch each other, are, in some cases, found to offer advantages over the fore- going, but for spans from 50 to 150 feet they are not generally found economical. The following are a few examples selected from bridges made at Crumlin of this class :— 1 span, 61 feet clear of the section given above, girders 5 feet deep. Tons cwts. Centre girder . . , . . 10 18 Two side girders . . . . . 17 12 Thirty-four cross girders . . . 13 12 Bracing . . . . . . 1 2 Bearing blocks ...........................1 15 45 0 for double line railway, rolling load 11 tons per foot run. 1 ditto, 47 feet span. One centre girder . Two side girders . Twenty-eight cross girders . Bracing . . . . Bearing blocks . • Tons cwts. 7 12 11 4 11 4 0 16 1 15 32 11 for double line of railway, ditto.