Memoirs and Proceedings - Manchester Literary and Philosophical Society Volume 14 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1851 edition. Excerpt: ... cause a deflection; and, supposing the depth of the girder at the pier to be 14 feet, we then have 125 feet, or half the span, as the distance of the point of greatest de The design for a Tubular Girder Bridge for supporting the Dublin and Belfast Junction Railway across the Boyne at Drogheda. flection on one side of the pier, which, acting as the fulcrum, or support of the beam, has a tendency to raise, or tilt up the end of the land girder to the same height exactly from the abutment pier. Assuming this to be the fact, and the girder to be perfectly rigid, we should then have a tensile strain along the top side of the girder over the pier in the ratio of 125: 14, nearly as 9:1. This is one of the advantages peculiar to the wrought-iron tubular girder, as, in every bridge having more than one span, the girders have always been made continuous; but as repeated changes are continually going forward from the passing trains, and as these changes, producing a severe strain, have a tendency to destroy the elasticity of the material, and the soundness of the workmanship at that part, I have considered it essential for the public safety to neglect it in the calculation, and to give in any additional strength which may arise from that source. Should it, however, be determined to take these advantages into account, a new formula must be deduced, and a new system of construction must be adopted over the piers, in order to attain the full benefit of this new element of strength. The excess of strength that should be given to Girder Bridges, has received considerable attention not only from the profession, but also from the general public. The various accidents which have occurred in the failure of bridges of dilferent constructions, have created of...