Journal of Civil Engineering and Environmental Technology p-ISSN: 2349-8404; e-ISSN: 2349-879X; Volume 3, Issue 6; April-June, 2016, pp. 553-557 © Krishi Sanskriti Publications http://www.krishisanskriti.org/Publication.html Seismic Vulnerability Assessment of an Existing Railway Bridge Shashikant G. Kothalkar 1 and Sachin B. Kadam 2 1 S.Y. M.Tech (Structure), Walchand college of Engineering, Sangli 2 Walchand College of Engineering, Sangli E-mail: 1 shashi2665@gmail.com, 2 sachin.kadam@walchand sangli.ac.in Abstract—Bridges plays a very important role in transportation network of any country, as in India, fifty percent area of country is susceptible to damaging earthquakes so the serviceability of bridges is a challenging issue for transportation. Seismic assessment of existing bridges comparative to existing buildings is less. So it is important to evaluate the seismic risk associated with an existing bridges and anticipate the possible damages that will occur in it under damaging seismic events. From the seismic assessment of an existing bridges, we will be able to take a rational decision whether an existing bridge can be left as it is or need retrofitting for future earthquakes. In the present study, a two span 18.3m P.S.C. Girder Bridge existed at chainage 74110m in railway route from Amravati–Narkhed (Amravati, Maharashtra, India) across Sukhi river is taken as a case study. Non-linear pushover analysis method can be used to evaluate the structural behaviour of bridges in the inelastic range and to get the failure pattern in different components of bridges when subjected to damaging seismic events. But in pushover analysis, only fundamental mode is considered as dominant. So this limitation of the pushover analysis method increases our attention towards seismic vulnerability assessment and development of fragility curves. So fragility curves are also developed for four different damage states ranging from slight damage to complete damage along with pushover analysis for the case study. Keywords: Prestressed Bridge, Seismic Vulnerability, Fragility curves, Nonlinear Static (Pushover) Analysis, SAP 2000 1. INTRODUCTION Indian Railways have many bridges and most of them are not designed according to modern seismic design codes. And also older structures show insufficient capacity like low deformation capacity. So it is requisite to do seismic assessment of an existing bridges. In the linear method of analysis, bridge action is within elastic range and results of the method like force and displacement are quite high. So it will make uneconomical bridge design. That’s why nowadays non-linear analysis like pushover analysis method can be used to know the non-linear behavior of the structure as well as to draw the failure pattern for different components of the bridges. So the first step of the project work is to carry out pushover analysis for the case study. But the main assumption of pushover analysis method is the response of the structure is mainly controlled by its fundamental mode. This force us to give attention on seismic vulnerability assessment and development of fragility curves. Modal analysis of a 3D bridge model reveals that it has many closely-spaced modes. Participating mass ratio for the higher modes is very high. Therefore, pushover analysis with single load pattern may not yield correct results for a bridge model. Fragility curves of bridges can be developed empirically as well as analytically. Empirical fragility curves are usually developed based on the damage reports from past earthquakes. Since earthquake damage data are very scarce in developing countries like India, analytical development of fragility is the only feasible approach of development of fragility curve. Analytical fragility curves are developed from seismic response analysis of bridges, and regression analysis of simulated response data to establish the probabilistic characteristics of structural demand as a function a ground motion parameter. 2. SCOPE AND OBJECTIVES: In this paper, an attempt is made to study and compare the effects of earthquake on an existing railway bridge using SAP2000 and to check its vulnerability. By using methodology of Hazard–US (HAZUS) (MH-MR1, 2003) variability in demand and capacity will be estimated and to obtain the fragility curves for the existing railway bridge by analytical approach. 3. NONLINEAR STATIC (PUSHOVER) ANALYSIS: Pushover analysis is a simplified, static, nonlinear analysis under a predefined pattern of permanent vertical loads and gradually increasing lateral loads. Typically, the first pushover load case is used to apply gravity load and then subsequent lateral pushover load cases are specified to start from the final conditions of the gravity pushover. Typically, a gravity load