Effect of Column Base Flexibility on the Hysteretic Response of Wide Flange Steel Columns

Recent experiments on wide flange steel columns subjected to multi-axial cyclic loading underscore the influence of the member end boundary conditions on strength and stiffness deterioration due to coupling of local and lateral torsional buckling. Field observations complemented by recent tests indicate a similar sensitivity of response modes to the base flexibility. This paper investigates the effect of the column base flexibility on the hysteretic behavior of first story steel columns in moment resisting frames (MRFs). This is accomplished through rigorous finite element (FE) simulations, validated by full-scale column member and column base tests. Recent studies on embedded steel column base connections are used to infer the base flexibilities used in the FE simulations; these are representative of those commonly observed in first story interior columns of mid- to high-rise steel MRFs. The FE simulation findings indicate that column base flexibility delays the onset of local buckling, and subsequently reduces the axial shortening by about 50% compared to the fixed-base case. In contrast, the column base strength itself is insensitive to the column base flexibility.