# A Text-Book of Roofs and Bridges Volume 1

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## Description

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. 1888 edition. Excerpt: ...in the proper position and the two adjacent chord stresses being found by moments, the difference of these is the horizontal component of the stress for the given diagonal. The bowstring truss is sometimes built without counter-ties, in which case the main ties take compression as well as tension, like the Warren truss. Prob. 63. Compute the maximum and minimum stresses for the members be, Cc, Cb, and Be in Fig. 48. Art. 39. The Parabolic Bowstring Truss. The apex points of the upper chord of a bowstring truss should be so arranged as to lie upon some regular curve, for evident aesthetic reasons. If this curve be a parabola the truss enjoys the remarkable property that under uniform load the diagonals are unstrained and the lower chord stresses are the same in all panels. To prove this let d be the center depth and / the span. Then for a uniform load of w pounds per linear foot the lower chord stress at any distance x from the left support is, wlx--wx y Fig. 49. in which y is the lever arm for the lower chord at the section. To find the value of y consider that the equation of the parabola with reference to its vertex is l-x) = md-y), I' and since x = o when y = o, the parameter m equals---y Hence, Inserting this in the expression for S, we find _ ivf SSd and because this is constant the lower chord stresses are all the same. Now referring to Fig. 48, it is seen that the diagonals can have no stress under uniform load, for the horizontal component of the stress in any diagonal equals the difference of the chord stresses in adjacent panels. If the span and center depth be given the above formula for y determines the depth at each panel point, so that the upper apex points may lie on a parabola. For instance, if / = 90 and d = 13, as in Fig. 48, we...show more

## Product details

• Paperback | 34 pages
• 189 x 246 x 2mm | 82g
• Miami Fl, United States
• English
• black & white illustrations
• 1236634667
• 9781236634665