Influence of base-plate connection stiffness on the design of low-rise metal buildings

Abstract

The objective of this research is to evaluate the influence of column base-plate connection rotational stiffness on the design of low-rise metal building systems. Currently, low-rise metal buildings are designed based on a zero rotational stiffness (pinned connection) assumption at the column-bases. Although prior research indicates that the assumption of zero rotational stiffness of the column base-plate connection could result in a significant underestimation of the overall lateral stiffness of horizontally loaded moment frames (leading to less economical designs), there has been no systematic study to investigate this issue. This paper first presents the details of an experimental research program that was conducted to quantify the rotational stiffness of “pinned” column base-plate connections that are commonly used in the low-rise metal building industry. Eight full-scale column base-plate connections with varying base-plate dimensions, numbers of anchor rods, anchor rod diameters, and gage distances were tested. Then, the data obtained were used to investigate the reduction in the total weight of gabled frames used in metal building construction. Finally, a piecewise nonlinear spring model was fitted to the test data to represent the rotational stiffness of the joints beyond the elastic range. Analyses of example frames indicate that consideration of the rotational stiffness of the pinned connections reduces frame deflections between 11 and 67% and has the potential to make metal building systems more economical by decreasing the frame weight between 0 and 12%, which is considered a substantial cost saving for the metal building industry where profit margins are relatively low.