Strength reserve-based seismic optimization for precast concrete frames with hybrid semi-rigid connections

To avoid premature yielding, excessive displacement, and unfavorable failure mode of precast concrete (PC) frames under strong earthquakes, a multi-objective seismic optimal design procedure for PC frames with hybrid semi-rigid connections is proposed. With the purpose of indicating the stiffness and inelastic displacement demands, the performance metric of yield strength reserve (YSR) is developed based on the strength reserve-related design concepts and the inelastic displacement spectrum. On this basis, the YSR is introduced as a performance objective for the optimization of PC frames, together with a customized objective of the structural cost. With specific consideration of the adaptability of hybrid semi-rigid connections, the non-dominated sorting genetic algorithm II is implemented to perform the inelastic seismic optimization. The feasibility and efficiency of the proposed approach are demonstrated on a 10-story PC frame. The widely dispersed Pareto front with diversified solutions obtained from the case study implies the prominent design flexibility of PC frames with hybrid semi-rigid connections. The seismic performance evaluation and comparison of selected optimal cases indicate that the structural performance was more closely associated with connection properties than the frame sections. Due to the existence of semi-rigid connections, a slight increase in the structural cost is observed to cause a significant increase in the YSR. More importantly, the structural response (e.g., inter-story drift ratio, connection rotation, and deflection mechanism) can be effectively controlled with a larger YSR.