Robust optimisation of RC bridge seismic design considering ground motion suite variability

Robust design optimisation (RDO) of performance-based seismic design (PBSD) has been established as a rigorous approach for obtaining optimal solutions that are minimally sensitive to record-to-record (RTR) variability of ground motions used in nonlinear response history analysis (NLRHA). However, this method is not able to explicitly account for the suite-to-suite (STS) variability due to the epistemic uncertainties associated with ground motion selection, especially when each suite is selected and scaled based on the requirements of the seismic design codes currently in force. To account for this uncertainty, this paper proposes a novel formulation for robust optimisation, which explicitly accounts for ground motion suite variability. In this method, one objective is to minimise the dispersion in the probability of limit state violation due to STS variability and the other objective is to minimise the economic costs. To increase the computational efficiency of the proposed method, surrogate seismic demand models are developed and applied to assess the probability of limit state violation. The application of the proposed framework is demonstrated using a case study of a typical reinforced concrete (RC) highway bridge with cylindrical piers, and the ability of the RDO framework to account for the STS variability is discussed. Finally, the Pareto-optimal solutions obtained from the proposed approach are compared with those given by the conventional RDO approach.