Maximum Stresses in Framed 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. 1878 Excerpt: ...be one or two-tenths of a foot lower then for economy. The amount saved though is not worth the computing, for in the change from a height of 28' to one of 27' the amount saved is only 740 lbs. as we find from the above. The time may more profitably be spent in ascertaining the best diameters of compression members for economy, regard being had to the castings and pins at the same time. 105. For the Whipple through truss, Fig. 9, we get from the table, art. 85, The influence of the diagonals is very small in our equation, since tan dBb= 50 or nearly 45 (art. 92). In a similar manner it is found that the height of the Whipple Deck Truss should be increased to 29 feet. 106. The Pratt Truss, through bridge, was next computed, for same span, loads, No. panels and height (2 b') as before. The strains have already been given. The end brace was inclined, as in Fig. 9. Using the lettering of that Fig. the posts Cc, Dd were given a diameter of 12"; the other of 8" to 10," the end brace and chord as before. On making out a " Bill of Materials," the total weight of bridge was found to be 333,800 pounds. From the table of weights, Wc =75,095 pounds. Ties and counters=Wt = 36914, also cos. 2i--A11 weights of the respective trusses 28' high. From eq. (14) we also ascertain that the Whipple Truss, for the diameters taken, might have a height of-fa foot, say over 29' with economy. The Pratt nas within a tenth of a foot of the most economical height for the dimensions given. 108. Let us now compare the weights of the three trusses examined for the most economical heights. As the diameters of the columns are unchanged, the same number of pounds of iron for castings, &c., was added as before. The section of the vertical posts in the triangular tru...