Question: Standard design practice as exhibited

Standard design practice, as exhibited by the solutions to Probs. 8–39 to 8–43, is to assume that the bolts, or rivets, share the shear equally. For many situations, such an assumption may lead to an unsafe design. Consider the yoke bracket of Prob. 8–35, for example. Suppose this bracket is bolted to a wide-flange column with the centerline through the two bolts in the vertical direction. A vertical load through the yoke-pin hole at distance B from the column flange would place a shear load on the bolts as well as a tensile load. The tensile load comes about because the bracket tends to pry itself about the bottom corner, much like a claw hammer, exerting a large tensile load on the upper bolt. In addition, it is almost certain that both the spacing of the bolt holes and their diameters will be slightly different on the column flange from what they are on the yoke bracket. Thus, unless yielding occurs, only one of the bolts will take the shear load. The designer has no way of knowing which bolt this will be. In this problem the bracket is 8 in long, A = ½ in, B = 3 in, C = 6 in, and the column flange is ½ in thick. The bolts are ½ in UNC SAE 5. Steel washers 0.095 in thick are used under the nuts. The nuts are tightened to 75 percent of proof load. The vertical yoke-pin load is 3000 lbf. If the upper bolt takes the entire shear load as well as the tensile load, how closely does the bolt stress approach the proof strength?

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  • CreatedNovember 10, 2009
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