The theory of strains in girders and similar structures; with observations on the application of theory to practice, and tables of the strength and other properties of materials - Softcover

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1869 Excerpt: ...than the same load at rest or moving but slowly, especially when the moving load is very large compared with the dead weight of the girder. The increase, however, is generally slight in railway practice, and the greater the weight of the structure is to that of the passing train the less will be the increment of deflection due to rapid motion. The difference of deflection caused by a locomotive crossing the central span of the Boyne Viaduct, 264 feet in the clear between supports, at a very slow speed and at 50 miles an hour was scarcely perceptible, and did not exceed the width of a very fine pencil stroke, but the increase of deflection is more marked in bridges of small span, as appears from the following experiments made on the Godstone Bridge, South Eastern Railway, by the Commissioners appointed to inquire into the application of iron to railway structures.f The Godstone is a cast-iron girder bridge, 30 feet in span, with two lines of railway. Tons. Weight of two girders,----15 Weight of platform between these girders,--10 Weight of half the bridge, i.e., permanent load, 25 Weight of engine,-----21 Weight of tender,-----12 Moving load,----33 Report, p. xi. t Report, App., p. 250. Similar results were obtained from the Ewell Bridge, upon the Croydon and Epsom Line. The span of the Ewell Bridge is 48 feet, the permanent weight of one-half is 30 tons, and the statical deflection due to an engine and tender, weighing 39 tons, was rather more than one-fifth of an inch. "This was slightly but decidedly increased when the engine was made to pass over the bridge, and at a velocity of about 50 miles per hour an increase of one-seventh was observed. As it is known that the strain upon a girder is nearly proportional to the deflection, it must be inferred t...