PSI - Issue 70

Surabhi Saxena et al. / Procedia Structural Integrity 70 (2025) 169–174

170

1. Introduction Bridges are the significant, prominent and major part of the transportation system. It becomes an important job for the engineers/designers to analyze the structural integrity of the bridge. The designing aspects of the bridges are judged with respect to the design codes. In the 1980s, it was observed that bridges faced more vulnerability due to improper design parameters and inadequate ductility. It was critically important to gauge the seismic vulnerability of bridges after the damage caused by major earthquakes such as, 1994 Northridge, and 1989 Loma Prieta earthquakes. The objective of seismic design of bridges is essential as transportation channels need to be in operational stage, depending upon three levels, where return period is 50 years, 150 years, and lastly more than 150 years of bridge’s lifespan (Thakkar et al., 2023). There are various methods to understand the seismic behaviour of bridges such as dynamic analysis and static analysis. Time history analysis gives the most accurate results as it depicts the time dependent response of the structure, but it is time consuming and demands more computational effort. With the past few years, fragility analysis has gained popularity among the different methods by the researchers and analysts. Although procedure for non-linear, static methods such as pushover analysis is same for buildings and bridges, but the load application is not certain for the bridges. So, uniform load applications are taken into account. In analysis of bridges, higher modes are involved, that makes conventional pushover analysis less accurate. Adaptive pushover analysis gives more reliable results for the non-linear static analysis of bridges (Perdomo et al., 2022). 1.1. Fragility Analysis Fragility analysis clarifies the seismic behaviour of the structure. It tells the susceptibility of the failure of the structure, that means the fragility curve depicts the probability of failure at different damage states. There are various fragility analysis studies that were developed over the years by researchers such as expert based fragility curve, empirical fragility curve and analytical fragility curves. Fragility=P[DS|IM=y] (1) Where, P=conditional probability, DS= damage state of the structure, IM= intensity measure or ground motion (Muntasir Billah & Shahria Alam, 2015). In the present study, analytical fragility curves are developed for two-span RC bridge. Pushover Analysis is a non-linear and static method, that is performed to achieve the capacity curve of the structure. It tells the variation of base shear force with respect to the displacement. This analysis is prerequired to conduct the fragility analysis. In this study, uniform load applications are considered in the x-direction. The bridge deck is assumed to be elastic and for non-linearity, plastic hinges (PM2M3) are assigned to the top and bottom of the reinforced concrete pier. Stiffness of the superstructure does not affect the response of the bridge as per the seismic excitation. The curve is transformed into bi-linear curve using capacity spectrum method. Yield displacement and ultimate displacement are noted, and finally yield ratio is calculated. 2. Previous Studies The seismic fragility analysis of southern and central US was done. The vulnerability was accessed, and retrofitting necessity was discussed (Choi & Jeon, 2003) . A simplified method for fragility curves was analyzed. The importance of structural parameters and over strength ratio was focussed (Karim & Yamazaki, 2003). A probabilistic seismic fragility analysis of Northern California highway bridges was investigated by (Zhang et al., 2020). The effects of bridge characteristics and seismic hazard levels were examined, and fragility functions were developed for several bridge types. The findings indicated that the likelihood of surpassing damage states rises as ground motion intensity and bridge age increase (Zhao et al., 2021). (Cao et al., 2020)also performed a seismic fragility analysis of continuous 1.2. Pushover Analysis