Connectivity-based seismic design strategy for bridge networks by controlling fragility correlation among individual bridges

The seismic connectivity of bridge networks, crucial for post-earthquake relief and reconstruction, is strongly affected by the fragility correlation among bridges, which is largely attributed to their similar dynamic characteristics. Previous research merely evaluated the effect of this correlation without addressing its control. This study proposes a connectivity-based seismic design strategy that adjusts design parameters to enhance and reduce fragility correlation on the same and different paths, respectively, while ensuring the bridge safety against the design seismic action. A design method is established, which involves identifying network information, deriving fragility and correlation models regarding bridge design parameters and site-specific earthquake conditions, and designing bridges within the network using these models. This method is demonstrated on a hypothetical network including bridges with isolation bearings. The results show that the fragility correlation mainly arises from the correlated demand related to dynamic characteristics, and impacts connectivity more than the bridge performance. The fragility and correlation of bridges are affected by seismic input angles and bearing parameters, and can be controlled by altering the latter based on the corresponding models. Compared to the network design focusing on fragility reduction, the proposed strategy effectively achieves higher connectivity reliability with lower costs for bridge improvements.