Seismic fragility evaluation of box deck concrete bridge equipped with shape memory alloy under bi-directional earthquake loading

Bridges are one of the most important elements of the transportation system in all countries. The collapse of a bridge or the time required for the repair of a damaged bridge can lead to traffic disruption and relief operation suspension that in turn results in the increased earthquake cascading tertiary effects. Therefore, reducing the vulnerability of bridges has always been the focus of engineers. The use of shape memory alloys (SMA) is one of the new solutions that have been presented and received attention in this field. The purpose of this research is to investigate the effects of using SMAs on the seismic behavior of straight box deck concrete bridges. For this purpose, a typical box deck concrete bridge is considered, and in the area of the plastic hinges of the bridge piers, the longitudinal steel bars are replaced with nickel-titanium SMA bars. The studied bridge is analyzed in two cases with and without the use of SMA under the effect of 3 categories of acceleration time histories, consisting of 120 strong ground motion records. Finally, the fragility curves for the maximum drift ratio and residual drift ratio values are calculated. The results show that the use of nickel-titanium SMA bars increases the maximum drift ratios and reduces the residual drift ratios. In this way, the permanent deformations will be decreased.