Fragility Analyses of Bridge Structures Using the Logarithmic Piecewise Function-Based Probabilistic Seismic Demand Model

Abstract

Seismic fragility analysis is an efficient method to evaluate the structural failure probability during earthquake events. Among the existing fragility analysis methods, the probabilistic seismic demand model (PSDM) and the joint probabilistic seismic demand model (JPSDM) are generally used to compute the component and system fragility, respectively. However, the statistical significance behind the parameters related to the current PSDM and JPSDM are not comparable. Aside from that, when calculating the system fragility, the Monte Carlo sampling (MCS) method is time-consuming. To solve the two flaws, in this paper, the logarithm piecewise functions were used to generate the PSDM and the JPSDM, and the MCS was replaced by the univariate conditioning approximation (UCA) method. The concepts and application procedures of the proposed fragility analysis methods were elaborated first. Then, the UCA method was illustrated in detail. Finally, fragility curves of a steel arch truss case study bridge were generated by the proposed method. The research results indicate the following: (1) the proposed methods unify the data sources and statistical significance of the parameters used in the PSDM and the JPSDM; (2) the logarithmic piecewise function-based PSDM sensitively reflects the changing trend of the component’s demand with the fluctuation of the seismic intensity measure; (3) under transverse seismic waves, major injuries happen on the side bearings of the bridge, while slight damage may occur on each pier, and as the seismic intensity measure increases, the side bearings are more likely to be damaged; (4) for the severe damage and the absolute damage of the studied bridge, the system fragility curves are closer to the upper failure bounds; and (5) compared with the MSC method, the accuracy of the UCA method can be guaranteed with less calculation time.

Seismic Fragility Assessment of an Existing Multi-Span RC Bridge Equipped with Risk Mitigation Systems

“…While these retrofit alternatives proved to have minor impacts on BDs, particularly for SL and MO performance limit states, additional retrofit alternatives are recommended to be combined with BRBs to control both the CD and BD demands of pre-seismic code multi-span simply supported bridges. As indicated in the assessment results of the as-built bridge, the lateral capacity and seismic performance in the transverse direction were significantly affected by CD demands (Figures 12,13,19,and 20). The adopted retrofit techniques for the considered benchmark bridge in this direction were effective under both considered seismic scenarios, particularly the far-field earthquakes that highly impact civil engineering structures in the UAE [37,49].…”

“…The adopted retrofit techniques for the considered benchmark bridge in this direction were effective under both considered seismic scenarios, particularly the far-field earthquakes that highly impact civil engineering structures in the UAE [37,49]. As indicated in the assessment results of the as-built bridge, the lateral capacity and seismic performance in the transverse direction were significantly affected by CD demands ( Figures 12,13,19,and 20). The adopted retrofit techniques for the considered benchmark bridge in this direction were effective under both considered seismic scenarios, particularly the far-field earthquakes that highly impact civil engineering structures in the UAE [37,49].…”

“…When the gap at the expansion joint or the stopper undergoes a relative movement in the negative direction (joint close) exceeding the gap width, the joint element begins resisting further opening (collisions). It is also noteworthy that other modeling approaches can be adopted, as recommended in previous studies [20]. The bridge bearings have lengths of 40 cm in the longitudinal direction and 25 cm in the transverse direction.…”

“…Recent studies have addressed evaluation approaches of existing bridges under earthquake loads, considering material degradation [18]. Recent studies have also conducted fragility analysis for the seismic performance assessment of complex structures, such as truss and cable-stayed bridges [19,20].…”

Analysis of time-varying seismic fragility of rigid frame pier of offshore bridge

“…The study of the performance of structures under ground motions has been a hot issue in recent years, and much work has been carried out by scholars on this subject. The vulnerability calculation method has been improved by the emerging technologies, such as artificial neural networks and so on (Morfidis and Kostinakis, 2019;Pang et al, 2021;Yuan et al, 2022;Zhao et al, 2021). Some researchers have conducted a series of explorations on the seismic characteristics and performance of frame results in environments such as far-field earthquakes, near-field earthquakes and strong earthquakes (Bhandari et al, 2019;Sharma et al, 2020a, b, c;2021a, b, c).…”