Seismic fragility evaluation of semi-rigid frames subjected to near-field earthquakes

Abstract The studies on the seismic fragility evaluation of semi-rigid (SR) steel moment frames are meager in the existing literature. The purpose of the present numerical study is to investigate the seismic fragility of SR frames subjected to near-field earthquakes. Specific characteristics of the fragility curves for near-field earthquakes are highlighted by comparing them with those for far-field earthquakes. A ten-story SR frame is analyzed subjected to four sets of earthquakes considering the moderate degree of semi-rigidity. The four sets of earthquakes, namely, far-field, near-field with high directivity, low directivity, and fling-step consist of ensembles of ten real ground motion records in each ensemble. The fragility plots are developed by considering a number of damage measures, namely, the maximum inter-story drift ratio, maximum base shear, maximum roof drift angle, maximum top-story acceleration with the peak ground acceleration (PGA) as an intensity measure. Threshold values for different damage states are decided based on the engineering judgment. For the near-field earthquake with directivity effect, the frequency repercussions on the fragility curves are investigated by varying the peak ground velocity (PGV) to PGA ratio with high ( > 160 cm/s-g), and low (