Investigating the Reliability of Nonlinear Static Procedures for the Seismic Assessment of Existing Masonry Buildings

Abstract

This paper presents, firstly, an overview of the nonlinear static procedures (NSPs) given in different codes and research studies available in the literature, followed by the results achieved by the authors to evaluate the reliability of the safety level that they guarantee. The latter is estimated by adopting the fragility curve concept. In particular, 125 models of a masonry building case study are generated through a Monte Carlo process to obtain numerical fragility curves by applying various NSPs. More specifically, among the NSPs, the N2 method (based on the use of inelastic response spectra) with different alternatives and the capacity spectrum method (CSM)—based on the use of overdamped response spectra—are investigated. As a reference solution to estimate the reliability of the nonlinear static approach, nonlinear dynamic analyses (NLDAs) are carried out using the cloud method and a set of 125 accelerograms; the results are post-processed to derive fragility curves under the assumption of a lognormal distribution. The focus of this investigation is to quantify the influence that the NSP method’s choices imply, such as the criteria adopted to calculate the displacement demand of a structure or those for the bilinearization of the pushover curve. The results show that the N2 methods are all non-conservative. The only method that provides a good approximation of the capacity of the analyzed URM structures as derived from NLDAs is the CSM. In particular, bilinearization is proven to have a relevant impact on the results when using the N2 method to calculate displacement capacities, whereas the CSM method is not affected at all by such an assumption. The results obtained may have a significant impact on engineering practice and in outlining future directions regarding the methods to be recommended in codes.

Seismic Resilience of G+6 Irregular RC Building: A Fragility Analysis

“…Recent studies have estimated the seismic fragility of building structures using a variety of techniques. In the domain of earthquake engineering, non-linear static procedures (NSPs), sometimes referred as pushover analysis, are frequently employed to evaluate the seismic performance of structures (Giusto et al, 2024). A series of nonlinear dynamic analysis are carried out for a range of progressively higher intensity levels of seismic ground motion using the incremental dynamic analysis approach (Mibang et al, 2022).…”

“…The outcomes demonstrate that none of the N2 approaches are conservative. The CSM approach is the only one that offers a reliable estimation of the examined URM structures capacity as determined from NLDAs (Giusto et al, 2024). When comparing the fragility curves produced by the nonlinear static procedure with those obtained from time-history analysis, Masanobu Shinozuka et al, claim that while there is excellent agreement when the damage is at least minor, it is not as good when the damage is major and nonlinear effects are obviously important [7].…”