Inelastic displacement ratios for evaluation of structures built on soft soil sites

Abstract

SUMMARYThis paper summarizes the results of a comprehensive statistical study aimed at evaluating peak lateral inelastic displacement demands of structures with known lateral strength and sti ness built on soft soil site conditions. For that purpose, empirical information on inelastic displacement ratios which are deÿned as the ratio of peak lateral inelastic displacement demands to peak elastic displacement demands are investigated. Inelastic displacement ratios were computed from the response of singledegree-of-freedom systems having 6 levels of relative lateral strength when subjected to 118 earthquake ground motions recorded on bay-mud sites of the San Francisco Bay Area and on soft soil sites located in the former lake-bed zone of Mexico City. Mean inelastic displacement ratios and their corresponding scatter are presented for both ground motion ensembles. The in uence of period of vibration normalized by the predominant period of the ground motion, the level of lateral strength, earthquake magnitude, and distance to the source are evaluated and discussed. In addition, the e ects of post-yield sti ness and of sti ness and strength degradation on inelastic displacement ratios are also investigated. It is concluded that magnitude and distance to the source have negligible e ects on constant-strength inelastic displacement ratios. Results also indicate that weak and sti ness-degrading structures in the short spectral region could experience inelastic displacement demands larger than those corresponding to non-degrading structures. Finally, a simpliÿed equation obtained using regression analyses aimed at estimating mean inelastic displacement ratios is proposed for assisting structural engineers in performance-based assessment of structures built on soft soil sites.

Estimation of peak displacements in steel structures through dimensional analysis and the efficiency of alternative ground-motion time and length scales

“…In this respect, many studies have focused on the prediction of maximum displacements in steel structures employing generic multi-storey frames [17,30] as well as equivalent single-degree-of-freedom (SDOF) systems [3,32,37]. Although the idealization of a multi degree of freedom structure as a SDOF system entails the neglection of a number of dynamic phenomena such as the contribution of higher modes, it has been recognised that equivalent SDOF models can provide a good basis for the estimation of global demands in building structures [27,31,35].…”

“…Even those studies that include varying levels of pinched response remain typically interested in reinforced concrete structures where important levels of strength deterioration are normally observed [14,33,37]. However, such levels of concurrent pinching and deterioration differ notably from the pinched hysteresis of typical PR steel systems where no significant deterioration in strength is evident up to considerably high levels of deformation demand [11,20,26].…”

Inelastic Displacement Ratios of Degrading Systems

“…The effect of strength softening was investigated by Miranda and Akkar (2003). Finally, RuizGarcia and Miranda (2004Miranda ( , 2006 developed inelastic displacement ratio plots for structures on soft soils. It is worth mentioning that in all the research work conducted by collapse potential was not considered.…”

Estimation of inelastic displacement demands of flexible-based structures on soft soils

“…Xu and Xie (2004) and Ziotopoulou and Gazetas (2010) proposed that the periods of an acceleration response spectrum should be normalised with respect to the spectral predominant period (corresponding to peak ordinate) in order to capture the peak spectral response. Similar suggestions have been made to improve the velocity (e.g., Mavroeidis et al, 2004;Xu and Xie, 2007) and displacement (Maniatakis and Spyrakos, 2012) response spectra, and also to modify the ductility reduction factor (e.g., Miranda and Bertero, 1994;Miranda and Ruiz-Garcia, 2002;Gillie et al, 2010), and inelastic displacement ratio (e.g., Miranda, 2000;Ruiz-García and Miranda, 2006;Iervolino et al, 2012) for nonlinear systems. However, all of these studies were restricted to fixed-base building systems and, therefore, the effects of soil-structure interaction (SSI) were not considered.…”