Effect of Column Base Flexibility on Earthquake-Induced Residual Deformations of Steel Columns

Post-earthquake residual deformations often control decisions regarding potential demolition of earthquake-damaged buildings. While residual deformations are typically assumed to be lateral, the column residual axial shortening has similar implications for such decisions. This paper investigates the effect of column base flexibility on residual axial shortening of columns in steel moment resisting frames (MRFs). The mechanistic reason for this dependency is that higher base flexibility reduces plastic rotation demands in the column, in turn mitigating local buckling-induced shortening. To investigate this issue, parametric finite element (FE) simulations interrogate various column sizes used in conventional mid-to high-rise steel MRFs. The simulations suggest at 1-2% story drifts, the base flexibility virtually eliminates the column axial shortening.