Rotational Stiffness of Exposed Column Base Connections: Experiments and Analytical Models

Abstract

The rotational flexibility of column base connections is often ignored in structural simulation of moment frames in which the bases are assumed to be either fixed or pinned. Although structural response is sensitive to base flexibility, methods to properly characterize base flexibility are not readily available. Motivated by these issues, a new approach to characterize the rotational flexibility of exposed column base connections is presented in this paper. The method leverages existing design procedures for base connection design, such that the rotational stiffness may be calculated with modest effort once the design has been completed. The method is validated through comparison with nine experiments, which interrogate a range of parameters including base-plate size and thickness, level of axial load, anchor-rod strength, and concrete strength. The comparison between the test and the predicted values indicates that, on average, the method predicts the stiffness with accuracy, such that the average test-to-predicted ratio is 0.89. The method is particularly accurate for conditions in which the moment-to-axial-load ratio is large, whereas it overestimates the stiffness of connections with high axial load, relative to the applied moment. A detailed analysis of the results is presented, accompanied by a discussion of the limitations of the proposed approach.