Excerpt from Report of the Engineer-in-Chief of the Illinois and St. Louis Bridge Company: May, 1868 By referring to Fig. 6 it will be seen that the bracing between the arch and the chord, as well as almost the whole of the chord itself, is suspended from the arch. In a span of 500 feet, these braces at the centre of the arch would be from 60 to 75 feet long, and their weight and that of the chord would be enormous; yet they bear no part of the load, but serve only to preserve the form of the how. The sole sustaining ...
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Excerpt from Report of the Engineer-in-Chief of the Illinois and St. Louis Bridge Company: May, 1868 By referring to Fig. 6 it will be seen that the bracing between the arch and the chord, as well as almost the whole of the chord itself, is suspended from the arch. In a span of 500 feet, these braces at the centre of the arch would be from 60 to 75 feet long, and their weight and that of the chord would be enormous; yet they bear no part of the load, but serve only to preserve the form of the how. The sole sustaining member of this truss is therefore the compressive member or arch. It must be evident then, that by sustaining that member between abutments we not only save the cost of the tension member and bracing, but we relieve the arch of this constant and enormous weight also. Now, if this bow-string truss were simply strong enough to bear its own weight before, the same arch supported between abutments, as in Fig. 7, and relieved of this weight, would then sustain an imposed load on the Bridge equally as great as the weight of the tension member and braces taken away. Indeed, if the span of the truss were 500 feet, these needless members would equal the weight of two loaded trains of cars throughout its entire length. It will be asserted that the ten sion member is all that is saved by using the abutments, because the bracing is needed to preserve the form of the arch also, when but one-half of the span is loaded, whether we use the tension chord or the abutments. This is true, but in the latter case a much smaller quantity of bracing material is needed, as I shall soon prove. I have purposely taken that form of truss which is of all others the most favorable to those who may be disposed to question the propriety of using the arch in the Bridge at this location, because in no other form of truss with the distributed load, even in theory. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at ... 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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