Fragility evaluation of steel truss railway bridges in Turkey

The objective of this thesis is to investigate the probability of failure of existing steel railway bridges in Turkey. In order to accomplish that objective, two multispan continuous bridges with total length of 154.5 m and 103.8 m; one simply supported bridge with total length of 96 m were investigated. Finite element models of those bridges were constructed through SAP2000 software based on original design drawings that were provided by TCDD, and they referred to as original bridge models. Furthermore, original models were compared with field measurements if available. In absence of field measurements, comparison was done with dynamic parameters which were obtained from previous studies. In case of more than 1% difference between relevant parameters, it was decided to develop original models. Consequently, new model, which was named as updated model, was generated with updating process. Three different soil classes were studied and earthquake records were determined with intent to obtain general earthquake behavior within the scope of typically used earthquakes in literature and Turkey. Subsequently, original and updated finite elements models were subjected to nonlinear time history analyses with selected earthquake records. According to obtained results from these analyses, fragility analyses of original and updated bridge models were performed and vulnerability curves of these were obtained. Fragility assessments were carried out for both circumstances and results were compared to each other. This thesis is composed of five chapters. In Chapter 1, general information about the study and the aim of the study are represented. Chapter 2 includes history and general characteristics about steel truss bridges, specifications of fragility curve development methodologies and summaries of previous studies related to fragility evaluation procedures. Chapter 3 describes the generation of analytically derived fragility curves within the scope of this study. The principles of selection of ground motion records, nonlinear time history analysis and modal updating procedure are included. Chapter 4 presents fragility evaluation results of case studies on selected single span and multispan continuous bridges. Finally, Chapter 5 is devoted to summary and conclusion of the study. Recommendations based on the results and conclusions of the study are also given in this chapter.