Investigating effects of various base restraints on the nonlinear inelastic static and seismic responses of steel frames

This paper deals with effects of various base restraints on the nonlinear inelastic static and seismic response of plane and space steel frames. The inelastic behavior is captured by a plastic fiber beam-column method, in which the beam-column member is monitored by integration points along the member length, and the cross-section is meshed into several sub-sections. The second-order effects are considered through the use of stability functions and the geometric stiffness matrix. The effect of shear deformation is also taken into account. The column-base restraint is simulated by using a multi-spring connection element developed by authors. The independent hardening model is employed for performing hysteretic loops of rotational springs under seismic loadings, whereas mathematical models are adopted for representing moment-rotation curves of those springs under static loadings. The accuracy and efficiency of the proposed program are compared with an experimental test, numerical examples of previous studies or SAP2000 commercial software. The results show significant differences of steel frames with various base restraints. Nonlinear semi-rigid base restraints perform strongly damping ability due to energy dissipation through moment-rotation hysteretic loops.