Probabilistic seismic fragility and loss analysis of concrete bridge piers with superelastic shape memory alloy-steel coupled reinforcing bars

Concrete bridge piers with conventional steel reinforcing bars are vulnerable to strong earthquakes by inducing significant residual deformations, which substantially weakens the seismic resilience of bridges. Superelastic shape memory alloy (SMA) bars showing superior self-centering capacities are desirable substitutes to steel reinforcements to minimize the seismically-induced residual deformations of piers. Nevertheless, high cost, difficult machining, and lack of sufficient energy dissipation are the primary restraining factors to a wide implementation of SMA reinforcements. This study proposes a novel SMA-steel coupled reinforcement for concrete bridge piers, which is intended to achieve the balance between self-centering and energy dissipation capacities. Probabilistic seismic fragility analyses are conducted on the prototype bridge with either pure steel, SMA-steel coupled, or pure SMA reinforcements to evaluate their probability of damage at different limit states. Seismic loss analyses are further performed to compare the relative cost-effectiveness of different patterns of reinforcements. The results indicate that an optimal amount ratio between SMA and steel bars can be found for the coupled reinforcements, which shows lower vulnerabilities and higher resilience under earthquakes than the other reinforcement patterns. The direct repair loss and the indirect downtime loss after earthquakes are considerably reduced when the SMA reinforcing bars are introduced. The coupled reinforcement with the optimal SMA-steel amount ratio shows the most effectiveness in mitigating the long-term economic impacts induced by seismic hazards within the lifetime of the bridge.