The Theory and Practice of Modern Framed Structures, Designed for the Use of Schools and for Engineers in Professional Practice Volume 3 (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. 1916 Excerpt: ...of bearing of the chords are nearly opposite each other, so that the resulting pin moment is still mainly dependent upon the difference in chord stress, or maximum diagonal stress, as in the other case. (See Chapter VIII for examples of pin calculation.) The maximum bending moment being known, the pin diameter is determined from the usual formula for fibre stress in beams, / = Mc/1. In this case c--radius of pin = r, and I = ir r/4-Expressing the result in terms of the diameter D we have / = 10.2 M/D and D = V 10.2 Ml = 2.17V AT//. Tables of resisting moments for various unit stresses and pin sizes are given in the handbooks. The allowable bending stress in pins may be taken fairly high, 24,000 lbs. per sq. in. in the Specifications, Appendix A. This is for the reason that the assumption of concentrated loads made in the calculations gives higher values than the true moments, and for the further reason that any slight bending of the pin results in some readjustment of the forces acting thereon, which tends to reduce the moments. The pin is also not subject to large additional stresses of a secondary nature, as is the case with the members themselves. The unit stresses employed are the result of many years, experience of bridge engineers in the behavior of bridges long in service. (3) Bearing Stresses.--The bearing stress on pins is taken, as in the case of rivets, at so many pounds per square inch on the area found by multiplying the thickness of the bearing by the diameter of the pin. For riveted members the necessary bearing area is provided by adding pin-plates to the member until the requisite thickness is secured. For eye-bars the bearing stresses may be limited to the desired value by a general provision limiting the ratio of pin diameter to the width...