Numerical Modelling of Exposed Base Plate Connections and Their Influence on System-level Seismic Response

Abstract

Gravity columns with exposed base plate connections are often assumed as pinned in both analysis and design. However, past experiments have shown that base plate connections can provide a significant level of flexural strength and stiffness. This study investigates the influence that the effect of base plate flexural strength and stiffness have on the global seismic response of steel structures. To capture the nonlinear response of exposed base plate connections, a detailed and simplified approaches to model exposed base plate connections are developed. To validate the proposed modelling approach in ABAQUS and OpenSees, it is compared with available experimental data in the literature. The results show that both developed modelling approaches can capture the nonlinear cyclic response of exposed column base connections and that the simplified model is suitable for conducting nonlinear time-history analysis. To investigate the influence of column base fixity on the system-level response of steel structures, the nonlinear dynamic response of a set of prototype single-story steel concentrically braced frames with flexible roof diaphragms was studied. The buildings are designed for a site in Vancouver, British Columbia and considered structures in regions with different hazard levels, soil classes and building dimensions to provide insight into the influence that the level of seismic demand and building geometry has on their response. Finite element models of each prototype structure were developed in OpenSees and were subjected to a series of ground motion records representative of the regional seismicity in Western Canada. Each prototype structure is subjected to the series of earthquakes with three different assumptions for the degree of base fixity: (1) pinned, (2) fixed, and (3) a realistic base plate connection. The results of the study show that the degree of column base fixity does not have a significant influence on the system-level response of the prototype structures, including maximum drift, residual drift, and maximum ductility demand on the bracing. These results suggest that a pinned base connection is a suitable assumption for single-storey steel braced frame structures.