Improved Seismic Design and Nonlinear Modeling Recommendations for Wide-Flange Steel Columns

Abstract

This paper presents the findings of parametric finite-element (FE) simulations of more than 5 wide-flange steel columns under cyclic loading. The column sizes, which are mostly highly ductile according to the current design practice in North America, are those seen in new and existing steel seismic-resistant moment frames. The parametric study is based on a high-fidelity FE model, which is thoroughly validated with available full-scale steel column experimental data. In the FE simulations, variations in the employed lateral loading history, the applied axial load ratio was considered to assess and refine a number of provisions related to the seismic design of steel moment-resisting-frame columns. The assessment is based on a number of performance indicators, including the column axial shortening and corresponding plastic hinge length, the column plastic rotation capacity influenced by local and global geometric instabilities, and the lateral stability bracing force demands. Empirical expressions are proposed to estimate these performance indicators as a function of geometric and loading parameters. Based on these expressions, seismic design recommendations are proposed to maintain column stability. A comparison is also made with current standards with respect to nonlinear modeling provisions for steel columns, and specific recommendations are proposed to update the limits for force-controlled wide-flange steel columns.