Flexibility of exposed column bases: Models and effects on seismic response of steel moment frames

Column base flexibility in Steel Moment Resisting Frames (SMRFs) is often not simulated, suchthat the bases are assumed to be fixed or free. This is attributable to the lack of reliable modelsfor simulating base flexibility, with the implication that the effect of base flexibility on seismicresponse of SMRFs is largely unknown. This paper addresses these issues by (١) presenting amodel for characterizing base flexibility, and (٢) applying this model through NonlinearResponse History Analysis (NRHA) to examine the effect of base flexibility on the seismicresponse of SMRFs. The model, which is based on the physical response of base connections, isdetermined to be accurate for a range of configurations when validated against experimentaldata. The model is applied within NRHA of ٢-, ٤-, and ٨- story SMRFs. The primary finding isthat the flexibility of base connections produces a soft first story, resulting in a reduction ofcollapse capacity relative to the fixed base simulation. Implications and limitations of theresearch are discussed.