Seismic assessment of plain concrete arch bridges by three dimensional simulation using geometrical and mechanical properties

There are numerous old arch bridges in Iran that have been used as railway bridges for more than seventy years. Since most of these bridges are not designed for earthquake excitation, seismic vulnerability of these structures is uncertain. This fact necessitates the investigation of the earthquake resistance of these kinds of bridges. To evaluate complex behavior of these bridges, results of field tests are required. Since it is not possible to perform field tests for all arch bridges, these structures should be simulated correctly by computers for structural assessment. Several parameters are employed to describe the bridges, such as number of spans, length, geometrical and material properties. In this study, results of field tests are used and adapted for 32 three dimensional finite element models with various physical parameters. Modal deformations of bridges at longitudinal and transverse directions is perceived from nonlinear computer simulations. Furthermore, Seismic performance of these bridges is assessed by pushover analysis in two directions and the capacity curves of the structures and linear demand spectrum are obtained using nonlinear static analysis method suggested by the Iranian standard. The crown is selected as a control node in the pushover analysis and its influence on seismic performance of plain concrete arch bridges is considered. Finally, the demand levels of the bridges based on 475 return period earthquakes are determined and compared with capacity curves. The results show that the performance of longitudinal direction is better than transverse direction, but the earthquake resistance of these kinds of bridges totally depends on the material properties and geometry of the structures.