Influence of site effects on inelastic displacement ratios for SDOF and MDOF systems

Abstract

Lateral displacements' control of structures subjected to earthquake ground motion has now been recognized as a key factor in the assessment of system performance, leading to design approaches that use displacements rather than forces as the starting point for the seismic evaluation of structures. In fact performance-based approaches offer significant advantages in comparison with traditional force-based approaches, since the former are capable of focusing on nonlinear behaviour and consequent damage to the structure, in contrast to the latter. Lateral displacement demand, particularly in structures that exhibit nonlinear behaviour, can be significantly affected by the features of strong ground motion, i.e., amplitude, frequency content and duration. Such characteristics are in turn profoundly influenced by the irregularity and changeability in earthquake ground motions, which should therefore be taken into account appropriately. The great number of strong motion records gathered throughout the last decades in the most widely varying soil-site conditions has made accounting for soil-site effects in the characterization of elastic and inelastic displacement demands feasible. The aim of this paper is to present the results of numerical investigations on the response of both single-degree-of-freedom (SDOF) and multiple-degree-of-freedom (MDOF) systems, through nonlinear time-history analyses performed on the basis of a wide data set of strong motion records. Constant ductility spectra of the ratios of the maximum inelastic displacement to the corresponding maximum elastic demand were derived for this purpose. In particular, the influences of earthquake magnitude, source-to-site distance, local soil-site conditions, ductility and hysteretic behaviour were quantified. Finally, simplified expressions for the ratio of the maximum inelastic to the maximum elastic displacement were established, in order to allow the evaluation of inelastic displacements for new or rehabilitated structures for which the global displacement ductility can be estimated, directly from the knowledge of the corresponding elastic demands. (c) 2007 Elsevier Ltd. All rights reserved

Inelastic displacement ratios for SDOF structures subjected to repeated earthquakes

“…(11)- (14) and Table 5. Similar expressions can be provided for any possible combination of local site conditions, seismic sequence, critical damping and post-yield stiffness ratios.…”

“…However, Miranda [7], Decanini et al [8], Ruiz-Garcia and Miranda [9,10] and Chopra and Chintanapakdee [11] showed that the inelastic displacement ratio can diverge significantly from unity in the moderately high to high frequency spectral regions. Recent investigations have shown that current standards used as the starting point for the seismic design of new structures, as well as of the seismic assessment of existing ones, can be significantly improved through an explicit account of lateral displacement demands [12][13][14][15]. The influence of various parameters on the inelastic displacement ratio is also examined in the abovementioned works.…”

Application of Wavelet Transforms on Characterization of Inelastic Displacement Ratio Spectra for Pulse-Like Ground Motions

“…Many research works have examined the evaluation of inelastic demands for structures under farfield ground motions [Miranda, 1993[Miranda, , 2000[Miranda, , 2001Chopra and Goel, 2000;Miranda and Jorge, 2002;Riddle et al, 2002;Decanini et al, 2003;Ruiz-Garcia andMiranda 2003, 2006;Mollaioli and Bruno, 2008]. It is well known that characteristics of ground motions close to the earthquake source can be considerably different from those of far-field motions in that they often contain a velocity pulse and permanent ground displacement [Somerville and Graves 1993].…”

Displacement damping modification factors for pulse-like and ordinary records

“…see [1][2][3][4]). In the performance-based philosophy, in fact, the design criteria are expressed in terms of achieving different performance objectives for different levels of seismic hazard [5,6].…”