Effect of two horizontal components of earthquake on nonlinear response of torsionally coupled base isolated structures

Abstract

SUMMARY Torsion in base‐isolated structures using bilinear rubber isolators effected by two horizontal components of earthquake simultaneously is investigated under various principal parameters including number of storeys; ratio of uncoupled torsional frequency to lateral frequency in the superstructure; ratio of uncoupled torsional frequency to lateral frequency in the isolation system; mass eccentricity in the superstructure and isolation system; and, in addition, the direction of eccentricity. Structure was supposed a shear structure and it was modeled by using concentrated mass and springs. Isolators are modelled by using nonlinear springs considering the interaction of isolator behaviour in two directions. The effect of variation in considered parameters on the behaviour of the superstructure and isolation system is investigated under seven ground motions. It is demonstrated that the parameters affect asymmetric structure behaviour with respect to symmetric one. The results of our investigations help us to understand the asymmetric structure behaviour under bidirectional earthquake by comparing it with a symmetric one. These results demonstrate that asymmetry in the superstructure or isolation system could have a significant effect on the torsional behaviour of isolated structures. In addition, the results show that the use of rigid superstructures and calculation of dynamic torsion by multiplying eccentricity by the dynamic base shear are unacceptable assumptions. Torsional effect on the isolated structural behaviour is amplified by considering two horizontal components of earthquake and comparing them with just one horizontal component. Copyright © 2010 John Wiley & Sons, Ltd.

Spatial seismic modeling of base‐isolated buildings pounding against moat walls: effects of ground motion directionality and mass eccentricity

“…In contrast to 2D simulations, structures analyzed in 3D can be subjected simultaneously to two orthogonal ground motion components, which is a more realistic way of representing actual seismic events in structural analyses. In the scientific literature, there are a number of studies that consider the coupling in both orthogonal horizontal directions subject to bidirectional excitations . Relevant analyses showed that the maximum horizontal displacement of a seismic isolator subjected to coupled bidirectional ground motion analyses can be higher compared with the uncoupled ones .…”

Torsionally Seismic Behavior of Triple Concave Friction Pendulum Bearing

“…In order to exert eccentricity in base isolation system (e b ), CM of base slab has been shifted with respect to CS of base isolation system. In parametric study, Ω tb is supposed to be one in all the models because of less effect of Ω tb on parameters such as the base displacement and the base shear (Khoshnoudian and Imani Azad 2011;Panchal and Jangid 2012) and uncoupled frequencies of base isolation system are calculated using the following equations:…”

“…Khoshnoudian & Azizi and Khoshnoudian & ImaniAzad (Khoshnoudian and Azizi 2007;Khoshnoudian and Imani Azad 2011) investigated the influence of various essential parameters on the seismic torsional behavior of base-isolated structures mounted on elastomeric bearings. It was noted that the superstructure in the torsionally coupled base-isolated structure doesn't behave as a rigid body which is a common assumption in the isolated structure design.…”

“…In addition, investigations on the effects of implementing isolation systems on asymmetric structures in comparison with symmetric ones illustrate that the torsion in asymmetric buildings makes the isolators' efficiency decreases respect to symmetric structures. The efficiency of isolators decreases significantly due to enhancing the eccentricity in superstructure and yield strength of isolators (Jangid and Datta 1994;Jangid and Datta 1995;Khoshnoudian and Azizi 2007;Khoshnoudian and Imani Azad 2011;Tena-Colunga and Escamilla-Cruz 2007;Tena-Colunga and Gómez-Soberón 2002;Tena-Colunga and Zambrana-Rojas 2006).…”

Behaviour of uni-axially loaded concrete-filled-steel-tube columns confined by external rings

“…There are different methods for the design of tall buildings subjected to extreme loadings (e.g. earthquake attack), which includes base-isolation methods (Khoshnoudian and Azad, 2011;Mehrparvar and Khoshnoudian, 2011;Yamamoto et al, 2011); installation of semi-active dampers (Ribakov, 2011a(Ribakov, , 2011b, active dampers (Ribakov and Agranovich, 2011a), passive dampers (Chung et al, 2009;Lee et al, 2009;Ribakov and Agranovich, 2011b) and tuned mass dampers (Heo et al, 2009;Marano and Greco, 2009;Mohebbi and Joghataie, 2012) and by reinforcement details such that a plastic hinge region can be formed to dissipate energy through inelastic deformation without structural collapse (Pam and Ho, 2009;Yan and Au, 2010). Amongst these measures, the last method is generally applicable to medium-rise and tall buildings for performance-based design approach (Sabol and Nishi, 2011), while the former methods are only cost-effectively for very tall buildings.…”