Evaluation of The Earthquake Behavior of Single Span Simply Supported Steel Railway Bridges by Fragility Curve

Fragility analysis is widely used in determining the earthquake performance of bridges. Determination of earthquake performances of railway bridges in Turkey which is located in the active earthquake zone is of great importance for preventing earthquake loss and material loss for possible earthquake scenarios. When the railway bridges in our country are examined it is seen that they are generally constructed in the late 19th century and early 20th century. Turkish Railway administration’s bridge inventory contains steel, masonry and reinforced concrete bridges, some of which are historical bridges. It is clear that detailed studies should be carried out to evaluate the seismic performance of bridges considering their long period service life and changes of technology and construction methodologies between their construction days and nowadays. In this study, a single-span steel railway bridge with simple support, which is frequently used in railway lines in Turkey is investigated. In order to make nonlinear analysis of the bridge, 30 different real earthquake records are selected in A, B and C ground classes. These earthquake records are scaled to 10 different shaking intensity values between 0.1 g and 1.0 g, and 300 nonlinear time-history analyzes are performed. The mathematical model of the bridge is constructed in accordance with the shop drawing with the help of commonly used finite element software. When the fragility curves are obtained, the maximum probability approach is used and the fragility curves of four different classes of damage are obtained for each bridge element. The results obtained are elaborated in detail. As a result of the analyzes, it is determined that the bridge supports are the weakest elements of the bridge. Intensity measure which causes 50% probability slight damage on bridge supports is 0.086g. The intensity measure, which causes 50% probability of damages for bridge superstructures, is 0.32 g. Redistribution of loads is not possible after plastic behavior is start in superstructure, for this reason the superstructure shows brittle behavior and moderate, extensive and complete damage are observed immediately after slight damage is reached. Considering the serviceability limit state, the analysis shows that increase in the use speed, increase the probability of failure. For the high risk seismic region use speed of Railway Bridge need to be restrained.