Base isolation for near‐fault motions

Abstract

Three analytical studies of base-isolated structures are carried out. First, six pairs of near-fault motions oriented in directions parallel and normal to the fault were considered, and the average of the response spectra of these earthquake records was obtained. This study shows that in addition to pulsetype displacements, these motions contain signiÿcant energy at high frequencies and that the real and pseudo-velocity spectra are quite di erent.The second analysis modelled the response of a model of an isolated structure with a exible superstructure to study the e ect of isolation damping on the performance of di erent isolation systems under near-fault motion. The results show that there exists a value of isolation system damping for which the superstructure acceleration for a given structural system attains a minimum value under near-fault motion. Therefore, although increasing the bearing damping beyond a certain value may decrease the bearing displacement, it may transmit higher accelerations into the superstructure.Finally, the behaviour of four isolation systems subjected to the normal component of each of the near-fault motions were studied, showing that EDF type isolation systems may be the optimum choice for the design of isolated structures in near-fault locations.

Performance of sliding systems under near-fault motions

“…This shows that all the three sliding isolation systems with their recommended parameters undergo almost the same peak displacement under near-fault motion. The corresponding average resultant displacement for a linear isolation system (with a period of 2.5 s and 10% damping) is 53.6 cm that is comparable with the resultant displacement of sliding isolation systems (Jangid and Kelly, 2000). Note that these displacement requirements under near-fault motion are relatively large to accommodate in the isolation system.…”

“…In the earlier code there were no near-fault factors but in the recent code, near-fault factors have been introduced that make it uneconomic to use isolation in such sites. Recently, there have been several studies for understanding the dynamic behavior of both isolated and fixed base structures under near-fault motion (Markis, 1997;Malhotra, 1999;Jangid and Kelly, 2000). It has been observed that the seismic response of structure under near-fault motion is quite different as compared to the corresponding response with farfault motion.…”

Passive and hybrid mitigation of potential near-fault inner pounding of a self-braking seismic isolator

“…NF ground motions are characterized by one or more intense long-period velocity and displacement pulses that can lead to a large isolator displacement [2,3]. Therefore, five NF ground motions of different intensities and various velocity and displacement pulses are considered to assess the performance of the RNC isolator damping and buffer mechanisms.…”

“…However, seismically isolated structures are expected to experience large displacements relative to the ground especially under near-fault (NF) earthquakes. The NF ground motions are characterized by one or more intense long-period velocity and displacement pulses, which lead to a large isolator displacement [2,3]. Such large displacements are accommodated by providing a sufficient seismic gap around the isolated structure.…”

Active neural predictive control of seismically isolated structures

“…[3] The pulse displacement is usually associated with the fault-normal direction, where high spectral acceleration components are observed in the long period range. [4] These long period spectral acceleration components tend to resonate with conventionally isolated structures, leading to an excessive base displacement that may destabilize the structure. To maintain the isolation deformations to within acceptable limits, two potential alternatives are to increase the effective stiffness of the isolation system or to provide additional damping mechanisms.…”