Response of middle-rise steel frames with and without passive dampers to near-field ground motions

This study analyses the response of middle-rise (6-stories) steel moment-resisting frame (MRF) with rigid joints subjected to near-field ground motions and also to artificial motions based on equivalent pulses. The near-field ground motions, recorded during the earthquakes in Northridge (1994), in Kobe (1995), and in Chi-Chi Taiwan (1999), show velocity and displacement peaks higher than the far-field ones. Indeed, in near-field areas other parameters are the key to defining the severity of the seismic input instead of the peak acceleration value. The ground motion velocity of fault-normal component is more severe than the velocity corresponded to fault-parallel component and presents large-amplitude pulses. The main objective of the present study is to acquire quantitative knowledge on near-field ground motion effects, to emphasize how these effects influence the structural response, and to point out the necessity to take into account the near-field effects in seismic design. Moreover, the responses of the aforementioned middle-rise frames equipped with shear link (SL) devices and subjected to near-field ground motions are discussed.