Effect of Uneven Standoff Distances on the Axial Force Resistance of Anchor Bolt Connections

Abstract

A stiffness-based approach founded on the moment-distribution method evaluated the effect of uneven standoff distances in double-nut anchor-bolt connections on the axial-resistive forces provided by the anchor bolts in response to connection loads. The uneven condition affected the intensity and distribution of resistive forces as determined when analyzed within the framework of the anchor-bolt group. The relative axial stiffness and proximity of the anchor bolts to the center of rigidity of the group were the major contributors. Comparisons with finite-element analysis showed close agreement for anchor-bolt configurations with even, uneven, and excessive standoff distances. The developed approach is comprehensive and applicable for various standoff distances, numbers, spacings, and sizes of anchor bolts. The approach is valid for fatigue-level (or greater) loads provided anchor-bolt stress does not exceed the elastic limit and the base plate supplies rigid diaphragm action.