Bolt Shear Design Considerations

In this paper, bolt shear capacities are reviewed using the Load and Resistance Factor Design (LRFD) philosophy. Only bolt-shear limit states are addressed, although one aspect of slip critical limit states is addressed incidentally. This paper does not consider bolt bearing limit states. Test data used to justify the adoption of ASTM A325 and A490 high-strength bolts was obtained from previous research programs. The data also included various types of rivets and Huck bolts for general comparison. First, the test data is used to evaluate the current American Institute of Steel Construction (AISC, 2005) and Research Council on Structural Connections (RCSC, 2004) bolt shear provisions and to determine the current reliability, beta, which is found to be conservative when based on a resistance factor, phi, of 0.75. The appropriateness of the phi-factor for bolt shear is addressed. Canadian (CSA S16-01) and Eurocode (EN 1993) provisions are also evaluated and shown not to be compatible with the test results. Two design equations are developed—one linear, one a step function—that result in a beta value slightly greater than 3.0, appropriate for a manufactured product. The single-step function (with a step at 38 in.) is recommended for inclusion in updated design specifications. This design provision increases the design strength by 12.5% for short connections and by 17.2% for long connections. The test data indicate that there is no need for a bolt strength reduction due to the length of the connection, provided that the connection material gross and net section areas exceed certain ratios. That ratio is a function of the connection material yield and tensile strength, the total bolt shear area and the bolt tensile strength.