Effects of Vertical Ground Motion on Highway Bridges

Due to the high probability of earthquake occur-rence in Iran and existence of large amount of faults near most of its cities, the probability of a near source earthquake with considerable vertical ground motion is high. This was indicated in Bam (2003) and Tabas (1978) earthquakes. Most of current earthquake design guidelines such as Iran bridge design provision either neglect the effects of vertical ground motion or use simplistic methods such as constructing vertical design spectra with 2/3 ratio of horizontal design spectra. However, recent research indicate that the consideration of vertical ground motion in design and analysis of structures particularly in near fault is necessary. A bridge designed with Iranian bridge design guideline is analyzed under near fault excitation and structure responses such as variation of axial forces, vertical moment at face of bent cap and vertical of death at midspan. For this propose, a finite element model of the mentioned bridge is modeled SAP2000 and dynamic analysis is conducted. Results indicate significant variation in responses.