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

Abstract

a b s t r a c tA seismic isolated structure is usually a long-period structural system, which may encounter a lowfrequency resonance problem when subjected to a near-fault earthquake that usually has a long-period pulse-like waveform. This long-period wave component may result in an enlargement of the base displacement and a decrease of the isolation efficiency. To overcome this problem, a rolling-based seismic isolator, referred to as roll-n-cage (RNC) isolator, has been recently proposed. The RNC isolator has a built-in buffer (braking) mechanism that limits the peak isolator displacements under severe earthquakes and prevents adjacent structural pounding. This paper addresses the problem of passive and hybrid mitigation of the potential inner pounding of the self-braking RNC isolator under near-fault earthquakes. Numerical results show that the RNC isolator can intrinsically limit the isolator displacements under near-fault earthquakes with less severe inner pounding using additional hysteretic damping and active control forces.

Influence of the characteristics of isolation and mitigation devices on the response of single‐degree‐of‐freedom vibro‐impact systems with two‐sided bumpers and gaps via shaking table tests

“…Seismic isolation systems are essentially designed to preserve structural safety and prevent occupants' injury and properties' damage. The major concept in base isolation is to diminish the fundamental frequency of structural vibration to a value lower than the dominant energy frequencies of earthquake ground motions …”

“…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 the isolator to undergo large displacements and—possibly—to be seriously damaged by exceeding the limit deformation and hence remaining permanently deformed or rupture can even occur. Such large displacements are accommodated by providing a sufficient seismic gap around the isolated structure.…”

“…Such large displacements are accommodated by providing a sufficient seismic gap around the isolated structure. In some cases, the width of the provided seismic gap is limited because of practical constraints …”

“…In rolling isolation systems proposed by Harvey and Gavin, Harvey et al and Harvey and Gavin, the limited rolling of steel spheres encapsulated between convex surfaces is employed in order to confine the displacement of the ball by means of a lip located at the border of every rolling surface. The roll‐n‐cage isolators limit the peak isolator displacements and prevent PADJS under strong seismic excitation by using a self‐braking mechanism, which contains the pounding inside the roll‐n‐cage isolator's frame. In friction pendulum isolators, if large displacements are attained, the slider element continues its motion on only one of the concave surfaces, when possible impact against the limiting ring prevents it to slide any longer on the other concave surface.…”

“…The major concept in base isolation is to diminish the fundamental frequency of structural vibration to a value lower than the dominant energy frequencies of earthquake ground motions. 1,2 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 the isolator to undergo large displacements [2][3][4] and-possibly-to be seriously damaged by exceeding the limit deformation and hence remaining permanently deformed or rupture can even occur.…”