Seismic performance of low-to-middle rise steel moment resisting frames with varied exposed column base

In low- to mid-rise weak-beam-type steel moment-resisting frames (MRFs), the lower ends of the first-story columns (column bases) are susceptible to yielding. Local buckling at the column base results in rapid deterioration, causing the column to lose its restoring force and thereby increasing the risk of complete MRF collapse. This issue is particularly pronounced when column bases are fixed (embedded). However, the rapid deterioration and MRF collapse can be mitigated by designing column bases to be either elastic or weaker than the respective columns. This study elucidates the influence of the elastoplastic behaviour of exposed column bases on the seismic performance of low- to mid-rise weak-beam-type steel MRFs. Response analyses were conducted on MRFs employing three types of exposed column bases – strong (elastic), weak anchor bolt, and weak base plate. The study findings are as follows: 1. In MRFs, no significant changes were observed in the maximum story drift angle in the first story and damages of the second-story beam utilizing weakly exposed column bases compared to those using elastic column bases. 2. The residual story drift angle in the first story is significantly smaller for MRFs using weakly exposed column bases than those using elastic column bases.