Many steel buildings, especially those with special moment-resisting frames (SMRFs), suffered failures at their column base connections during the 1995 Kobe, Japan, and the 1994 Northridge, and 1989 Loma Prieta, California, earthquakes. These failures prompted a need to investigate the reliability of current column base designs.
A parametric study was carried out on a typical low-rise building in Berkeley, California, featuring a SMRF with column base rotational stiffness varying from pinned to fixed. Pushover and nonlinear time history analyses carried out on the SMRFs indicate that the seismic demand in SMRFs with stiff column base connections approaches that of SMRFs with fixed column supports. Reduction in the connection’s stiffness resulted in damage concentration that could induce an undesirable first-story soft-story mechanism. System reliability analysis of the base plate connection was carried out to evaluate the system’s safety with respect to its diverse failure modes, as well as the adequacy of the limit-state formulation based on the AISC Design Guide No. 1-2005 procedure.
This study illustrates the importance of an accurate evaluation of the mechanical characteristics, the reliability, and the failure modes of the column base connection, and provides guidance for formulating performance-based design criteria, including impor tant considerations of the economic feasibility of the structure.
Keywords: Semi-Rigid; Pushover; Time-History; Performance-Based; Seismic.
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