Modelling aspects of structures isolated with the frictional pendulum system

Abstract

SUMMARYDifferent modelling aspects of structures isolated using the frictional pendulum system and subjected to earthquake ground motions are studied herein. Although the vertical dynamics of these structures is given special emphasis, other effects such as large isolator deformations and bidirectional input motion are also considered. Different structural models of the FPS are developed and tested for single-storey structures and a real four-storey building frame; among them, an 'exact' formulation of the FPS force-deformation constitutive relationship is presented. Results show that global building responses can be computed within 20 per cent error in the mean using a simplified model that ignores the vertical motion of the building; however, structural member deformations and forces need to be computed using a model that considers such motion. This is of particular importance when there exist correlation between the horizontal and vertical components of ground motion. Further, a physical model of the FPS is introduced and used to determine the response of a real four-storey frame, including uplift and downward impact. Results from this analysis show that local column responses may vary substantially depending on the stiffness of the isolation storey and the presence of a mass at the isolation level. Such mass is capable of filtering the large increase in column shear that results from the impact of the structure after uplift. Uplift occurs at several instants of the response of the structure considered, leading to an increase in column base shear as large as 3 times the shear obtained by ignoring the vertical dynamics of the building.1998 John Wiley & Sons, Ltd.

An experimental study of nominally symmetric and asymmetric structures isolated with the FPS

“…If the normal forces in the isolators are known, the pendular component of the restoring force would be determined accurately. For the sake of brevity, the equations used to produce a good analyticalexperimental estimate of the normal force are skipped in this presentation [6]. Once the frictional component of the restoring force Q …”

“…Response values deÿned next are computed directly from recorded accelerations and displacements by using simple equilibrium and kinematic equations [6]. These responses are: (i) the lateral deformations between the CM of the base slab and the ground (platform), q x and q y ; (ii) the total restoring force of the isolation system, Q b ; (iii) the deformations of the x , and torque T ( j) .…”

“…It is intended also that the experimental results obtained from this study may serve as a benchmark for later analytical studies of lateral torsional coupling of structures with the FPS. Because similar results have been obtained for the cases of sti ness and mass asymmetry [6], this research will just focus in the case of mass asymmetry in the superstructure.…”

An Efficient Order Reduction Strategy in Earthquake Nonlinear Response Analysis of Structures

“…For additional information about friction pendulum systems the reader is referred to the relevant literature (e.g. [33], [34], [35], [36], [37] and [38]). More detailed examination of this topic would lead beyond the scope of this paper, which should focus more on the methodical extension of the new MOR strategy as well as the application on a complex realistic system.…”

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

“…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].…”