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

Abstract

SUMMARYThis experimental investigation deals with the earthquake behaviour of a nominally symmetric and a mass-asymmetric three-storey structural model isolated with the frictional pendulum system (FPS). Both accidental and natural torsion are evaluated in the structure by using recorded accelerations in all building oors and measured deformations at the isolation level. A 3D-shaking table was used to subject the model to ÿve di erent ground motions, including impulsive as well as far-ÿeld subductionzone type earthquakes. Results show that the analytical predictions of the earthquake behaviour of the isolated structure, as obtained from a physical model of the FPS, are in close agreement with the true complex inelastic measured behaviour of the FPS. Besides, experimental results also validate previous observations about the importance of accounting for the variability of the normal loads in modelling the earthquake behaviour of FPS isolators. Measured torsional deformation ampliÿcations at the base of the building vary, in the mean, from 2.5% to 6% for the symmetric and asymmetric structural conÿgurations, respectively. In relation to the ÿxed base structure, the reduction factors for the base shear of the isolated structure are, in the mean, about 3.9 for both conÿgurations. Finally, it is concluded that the FPS is capable of controlling the lateral-torsional motions of mass-asymmetric structures quite e ectively by aligning the centre of mass of the superstructure with the centre of pendular and frictional resistance of the isolation system.

Characterizing rotational components of earthquake ground motion using a surface distribution method and response of sample structures

“…14 and 15), which is attributed to the significant fluctuations of the vertical load on each isolator due to the rocking components of ground motion. This observation is consistent with that of De-La-Llera and Almazan [11].…”

“…15. All combinations involving rocking input (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15) show fluctuations of lateral forces in the hysteresis loops (see, for example, panels d-f in Figs. 14 and 15), which is attributed to the significant fluctuations of the vertical load on each isolator due to the rocking components of ground motion.…”

Semi-active control of a torsionally-responsive structure

“…{rms(x POFF i )} (13) wherex is inter-story drift and isx the absolute acceleration of a floor. Here the superscript POFF denotes the case where the MR dampers are operated in the passive-off mode and no command voltage is sent to the dampers.…”

“…Here a 9 m tall, 3-story, 2-bay reinforced concrete structure with an eccentric stiffness derived from a shear wall is investigated by means of physical tests. Three 1.5 kN MR dampers An experimental investigation by de la Llera and Almazán [13] considered passive isolation devices to minimize the torsional responses of symmetric and asymmetric floor plans. Parametric studies determined optimal positions of employed friction isolation devices.…”

Seismic isolation analysis of FPS bearings in spatial lattice shell structures

“…Previous studies have been concerned with the simplifi ed model and experimental validation of the FPS performance (Zayas and Mahin, 1990;Mokha et al, 1991;Mokha et al, 1996) and other important aspects such as modeling of constitutive relationships and refi nement of the model of multi-story frame structures isolated by FPS (Almazan et al, 1998;Almazan and De la Llera, 2002;De la Llera and Almazan, 2003;Gilberto et al, 2004). However, studies on the seismic isolation of spatial structures with FPS have not been widely reported up to now.…”