Journal of the Franklin Institute, Vol. 17 of 47
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| Stand: | 2015-08-04 03:50:33 |
Produktbeschreibung
Excerpt from Journal of the Franklin Institute, Vol. 17 of 47: Of the State of Pennsylvania, for the Promotion of the Mechanic Arts The proof weight was fixed at 240 tons, as being double the greatest load which the bridge can, by any possibility, be ever required to bear. A heavy goods train weighs less than half a ton per foot lineal; a train, consisting entirely of locomotive engines, (which would be the heaviest of all possible trains,) would only weigh one ton per foot lineal, and, consequently, would place a load of not more than 120 tons on a bridge of 120 feet span. The new bowstring bridge has, therefore, been proved to twice the weight which ever can be placed upon it, and to four times the weight which it is ever likely to have to bear. It is scarcely necessary to add, that the trial gave great satisfaction to all parties. These ribs are adapted for large spans, in cases where either headway is of importance, or where sufficient abutment cannot be obtained, without very heavy expense. Bridges constructed of these ribs, may be employed with perfect safety for very large spans, in precisely the same manner as ordinary girders are used for small ones. The strength of the bridge depends upon the rib, or arch, and on the tie bars, by which the extremities are held together. The vertical standards are introduced, partly to suspend the load from the arch, and partly to obtain longitudinal and transverse firmness; they also support the tie-bars. The diagonals are employed for the purpose of preventing undue deflection in the rib, when the bridge is unequally loaded. The rib itself is constructed of boiler plates and angle iron riveted up in the form of a square hollow trunk; it is strongly tied together, so that the full section of the plates and angle iron may be depended upon, to resist the crushing strain. In order to give this trunk additional lateral stiffness, the side plates, which form the top, are made to overhang, and are strengthened on the edges by angle iron, &c. The tie-bars measure about 8 inches by 1 inch each, and are introduced in sufficient numbers to take the whole strain. The ribs are supported at each end, on cast iron shoes, fixed at one end to the piers, and mounted at the other on sliding frames and rollers. This arrangement provides not only for expansion and contraction, but also for motion under a very heavy load. The action of these parts, under proof, has been found to be perfect. Cross girders, constructed entirely of wrought iron, are suspended between the ribs. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.
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