Prying Action- A General Treatment

Abstract

The 8th Edition AISC Manual uses a model for predicting the prying force which was recommended in the book by Fisher and Struik. Unlike the approach taken in the 7th Edition Manual, this method is not restricted to specific bolt-plate combinations, since all major parameters which influence the prying action are included in the model. The Q denotes the prying force per bolt and is assumed to act as a line load at the edge of the flange. Test results have shown this to be a reasonable assumption for conditions near ultimate, as long as the edge distance a is within certain limits. The tensile load in the fastener is Bc, and the corresponding applied load per bolt is equal to T. The bending moment at the interface between the web and the flange is taken as Mc, and the moment at the bolt line due to prying force Q is taken equal to daMc where d is equal to the ratio of the net area (at the bolt line section bb)and the gross are a (at the web face section aa) of the flange. The a represents the ratio between the moment per unit width at the centerline of the bolt line and the flange moment at the web face. When a = 0, it corresponds to the case of single curvature bending, i.e., no prying action, and a = 1 corresponds to double curvature bending and maximum prying action. Note that, from physical considerations, 0 <= a <= 1.