A Superelastic Retrofitting Method for Mitigating the Effects of Seismic Excitations on Irregular Bridges

Irregularities in bridge pier stiffness concentrate the ductility demand on short piers; while not operating on the longer and more flexible ones. The existence of non-uniform, ductility demand distribution in bridges significantly influences seismic response. As such, this paper proposes a new approach for balancing the ductility demand in irregular bridges by utilizing shape memory alloys (SMAs). An irregular, single column bent viaduct with unequal pier heights is modeled and used as a reference bridge. To enhance seismic behavior of the bridge, a fixed bearing at the top of the short pier is replaced by a sliding bearing and two groups of SMA bars. SMAs are designed to keep their maximum strain within the super-elastic range. The seismic response of the controlled bridge is compared with a reference bridge through parametric studies using a set of suitable ground motion records. Study parameters include SMA lengths, short pier reinforcement ratios, design strain of SMA elements, and the heights of the medium and long piers. The proposed method successfully reduced the response of the short pier and, hence, improved the overall seismic behavior.