Seismic Assessment of Six-Meter Spans Plain Concrete Arch Bridge

There are a large number of old arch bridges in Iran that have been serving as railway bridges for more than seventy years. Field load testing of an old railway bridge in km-24 of Tehran-Qom railway has revealed important characteristics of the bridge and has proven that there is still a large capacity under service load. It is known that most of these bridges are not designed for earthquake and their seismic vulnerability is uncertain. This fact necessitates the investigation of earthquake resistance of these kinds of bridges. In this paper, an attempt has been made to assess seismic performance of the bridge. The bridge is a plain concrete arch structure with five six-meter spans, which has built 70 years ago. The results of dynamic load test have used to calibrate a finite element model of the bridge in which a plain strain analysis has been carried out. Vertical displacement of the arch is used as the calibration criterion. To investigate the seismic performance of the bridge, a nonlinear static analysis (pushover analysis) method is applied. Choosing several points as a control ones, the choice of control points in the pushover analysis of masonry arch bridges and its influences on seismic evaluation is investigated. The capacity curve of structure and damage levels is drawn and the creation of hinges due to the lateral loading are studied. Finally, the capacity curves and the nonlinear demand spectrum are drawn and the performance of the structure is determined. The results show that these kinds of structures are still strong under seismic exciting.