it has been known since the 1950s that under certain conditions, earthquake ground motions can consist of a limited number of strong acceleration pulses. These types of ground motions have come to be referred to as "pulse-type" ground motions. However, it has only been recently, following the Northridge earthquake (1994), that their importance for the earthquake resistant design of civil engineering structures has been recognized and introduced into the seismic provision of building codes through the introduction of the near-source factor [UBC, 1991-1997]. In an earlier paper [Anderson and Bertero, 1987] it was shown that the deflections, including lateral displacement, interstory drift and inelastic rotation, in a mid-rise steel buildings were increased significantly when the moment frame was subject to ground motions recorded in the near fault region during the Imperial Valley earthquake (1979) It has been shown that these types of ground motion can be particularly severe on the lower story levels causing increase drift demands and concern over increased second order P-Δ effects. Following the Northridge earthquake concerns were expressed for the safety of highrise buildings which may be subjected to pulse-type motions. Thus it was decided to conduct the current study of medium to tall buildings, both traditional strategies and innovative procedures for improving the performance of these structural systems were investigated.
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