Report of Board of Engineer Officers as to Maximum Span Practicable for Suspension Bridges (Paperback)

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. 1894 Excerpt: ... component is the weight on the half span, -j-. If T represents this maximum stress we obtain 4 '" 8 8 If we represent by Li the limiting span, that is, the span at which the cable will carry its own weight.with a given stress per unit of crosssection without carrying any other load whatever, we obtain from the above equation, by making p, --O and L=Lj T_w U VK'+IC 8 hence p'+w_Lt w L From the above equations we obtain 8T WW+ 16 For metallic towers and large spans the value K=8 will be generally about the most economical value for the ratio of the span to the cableversiue, when the cost of the foundations is taken into consideration. If we make It = 8 and substitute for T the working strength per square inch of the material of the cable, which we have assumed as 60,000 pounds, and for w the weight of a linear foot of the cable measured horizontally and having a cross-section of one square inch, which is 3.54 pounds, we obtain I=15160 feet; and J'+ic_15160 w L The values of p, and w in pounds, as determined previously, are as follows: j-'=13003 + 27704726 L '+ 3.24906 L + 0.0005.5335 L2+ 0.000000003L3 ic=17917. Substituting these values and reducing we obtain 31522 L + 3.24906 L2 + 0.00055335 L3 + 0.000000003 L4=243850994, the solution of which gives for the practical maximum span L=4335 feet. This span is measured between the highest points of the cables at opposite ends of the bridge. The Board consider this a conservative value of the maximum span, as it is based upon assumptions well within the limits of theory and experience. The elements of the bridge, deduced by the preceding formulas, are as follows: Span between tops of cables feet.. 4, 335 Height of towers above masoury do... 707 Number of cables 16 Diameter of each cable with wrapping inch...