Aziz Hosseinnezhad - Faculty of Engineering, Department of Civil Engineering, University of Mohaghegh Ardabili, P.O. Box ۵۶۱۹۹-۱۱۳۶۷, Ardabil, Iran.
Amin Gholizad - Faculty of Engineering, Department of Civil Engineering, University of Mohaghegh Ardabili, P.O. Box ۵۶۱۹۹-۱۱۳۶۷, Ardabil, Iran.

Long-span bridges, as vital structures, play an important role in economic development. Previous studies revealed that the seismic responses of such structures, under non-uniform excitations, are different from the same result due to uniform excitations. Furthermore, the results of several earthquake-damaged bridges showed that their seismic behavior was different from that predicted under uniform excitation and, in some cases; the responses were more than predicted results. Therefore, the damaged bridges under non-uniform excitations were re-analyzed and the obtained results were in good agreement with the recorded outcomes. Considering current bridge designing codes it is clear that almost all of them ignored it and just the Euro Code ۲۰۰۸ prepared some recommendations. It is found that the main reason for the differences in results from the uniform and non-uniform excitations is the spatial variation of earthquake ground motions. Based on the papers three phenomena were introduced for spatial variability of ground motion: the wave-passage, the incoherence, and also the site-response effects. The responses of structures under non-uniform excitations obtained from the superposition of dynamic and pseudo-static components. This paper investigated the seismic behavior of a long-span structure under non-uniform movements to evaluate the most undesirable conditions. So, different soils and load combinations considered and soil-structure effects included. The effect of wave-passage, incoherence, and site-response on the structure was measured and the results were compared with the uniform excitation. The results indicate that the variation in soil condition significantly affects the seismic responses under non-uniform excitations. Also, it is found that the results from uniform excitations with considering soil-structure interactions are remarkably increased. Moreover, the outcomes of analysis under-considered load cases and soil conditions showed that ignoring the spatially varying ground motions may lead to a non-conservative design.

Long-Span Bridges, SVGM, Pseudo-Static Response, SSI