Effect of Bolt-Hole Clearance on the Ultimate Strength of Eccentrically Loaded Bolt Groups

Abstract

The instantaneous center of rotation method is presented in the AISC Steel Construction Manual for the design of eccentrically loaded bolted connections. Tabulated values for normalized strengths of bolt groups are provided, and per the classical approach, bolt hole clearance is neglected in the formulation of the results. This study extended the method to consider the effect of bolt hole clearance on the ultimate strength of the bolt group. For vertically applied loads, accounting for the standard hole clearance resulted in, on average, a 2% reduction in the predicted strength of a bearing-type connection when using bolts of diameter less than 25 mm (1 in.) and a 6% reduction for bolts 25 mm (1 in.) diameter or greater. Accounting for the clearance from oversized holes resulted in, on average, a 9%, 14%, and 19% reduction in predicted connection strength for vertically applied load for bolts of diameter less than, equal to, and greater than 25 mm (1 in.) diameter, respectively. The results indicated that neglecting the hole clearance may be unconservative when considering the bearing strength of an eccentrically loaded bolted connection. Based on a probability study, potential factors are proposed to modify the AISC published ultimate strengths. A simplified approach to modeling the slip behavior of individual fasteners using an incremental analysis demonstrated that the slip-capacity of a fastener does not influence the ultimate strength of the connection.