Structural optimization of vertical isolated rocking core-moment frames

Dual earthquake-resistant archetypes suffer residual damage following a severe earthquake leading to socio-economic drawbacks. A vertical isolated rocking core-moment frame (VI-RCMF) provides a resilience technique to curtail the seismic vulnerability using the isolation of subsystems. Viscous dampers, installed at each floor level of the VI-RCMF archetype, separate moment frame (MF) from rocking-core (RC). The self-centering RC performs as a passive strong-back core, which can uplift on its toes. Although the VI-RCMFs have exhibited superior performance compared to non-isolated dual frames, there are analytical challenges to come up with the optimal design due to the complex interaction of subsystems. This paper presents an optimization framework for quantifying the optimal design parameters of VI-RCMFs. Accordingly, the simultaneous perturbation stochastic approximation (SPSA) method is employed as the optimization algorithm. The objective function is defined to minimize the displacement of MF and the design vector includes mass, stiffness, and damping ratios. The SPSA optimization analyses are conducted for a set of archetypes using OpenSees software. Optimal normalized responses of subsystems are computed for 44 far-field ground motions and aleatory uncertainties are quantified for optimal design variables. The results demonstrate the effectiveness of the proposed procedure for optimizing VI-RCMFs. The derived optimal design vector can be used for the preliminary design of low-to mid-rise archetypes.