Uplift-restraining Friction Pendulum seismic isolation system

Abstract

SUMMARYThis paper extends the scope of seismic isolation by introducing an innovative uplift-restraining Friction Pendulum system. Termed the XY-FP isolator, the new isolation device consists of two orthogonal opposing concave beams interconnected through a sliding mechanism that permits tension to develop in the bearing, thereby preventing uplift. Owing to its distinct conÿguration, the XY-FP isolator possesses unique properties for a seismic isolator, including uplift restraint, decoupling of the bi-directional motion along two orthogonal directions, and capability of providing independent sti ness and energy dissipation along the principal horizontal directions of the bearing. The study concentrates on introducing the concept and establishing the underlying principles of operation of the new XY-FP isolator, formulating the mathematical model for the XY-FP isolator, and presenting its mechanical behaviour through a displacement-control testing program on a single XY-FP isolator.

A Review of Seismic Isolation for Buildings: Historical Development and Research Needs

“…In certain situations uplift in the bearings could occur, e.g., bearings on the perimeter of slender structures or those located under braced frames. For these situations resistance to uplift is considered desirable and a tension-capable sliding bearing, based on the principles of the single FP bearing, was developed [50,51]. The tension-capable device, referred to as the "XY-FP" isolator, consists of two orthogonal concave sliding rails connected through a sliding device that couples the rails in the vertical direction, allowing for the development of tensile forces in the bearing.…”

Comparison of Friction Models for the Curved Surface Sliding System in the Nonlinear Seismic Analysis of Base-Isolated Buildings

“…The axial load acting on a CSS bearing can be modified in accordance with the following expression which also accounts for the verticalhorizontal coupling [18] …”

Nonlinear Dynamic Behaviour of Base-Isolated Buildings With the Friction Pendulum System Subjected to Near-Fault Earthquakes

“…In particular, at any given moment during an earthquake, the weight (W) of the superstructure acting on a FP bearing can be modified in accordance with the following expression [9] ,…”

“…Specifically, fling-step and forwarddirectivity in near-fault areas can produce long duration pulses of intense velocity in the horizontal direction [4,5], amplifying the displacement and inducing torsional and re-centring problems [6,7]. On the other hand, since the response of the FP system during the sliding phase is strongly influenced by the axial load, amplification of torsional demand and residual displacement and uplift of the FP bearings may also be induced by the high frequency vertical component of near-fault earthquakes [8][9][10]. This vertical motion is characterized by peak ground acceleration higher than the horizontal one and closer in time for decreasing values of distance from the fault [11,12].…”