An initial subsystem stiffness-integrated seismic performance optimization approach for super high-rise frame-core tube structures using generalized models

Complex super high-rise frame-core tube (FCT) structures often present numerical challenges during seismic optimization due to their numerous components and high lateral stiffness requirements. In response to these challenges, this study proposes an efficient initial subsystem stiffness-triggered optimization and performance control strategy, developed through newly created nonuniform flexure-shear coupled models (FSM-MS) and hybrid rocking models (HRM). A physically rational link is established for the estimate of subsystem stiffness of FCT structures by HRM and FSM-MS via the distributions of overturning moments and shear forces. The variations in dynamic properties resulting from stiffness degradation in concrete core tubes and exterior columns, as well as the vertical displacement ductility demand of steel outriggers, are utilized to assess the damage of each subsystem within the four-level performance-based seismic design framework. The subsystem damage is incorporated into the formulation of a multi-objective optimization problem, with structural cost and collapse margin ratio as the objectives, and constraints defined from three distinct aspects. The convergence, computational efficiency and stability of the proposed optimization strategy is systematically demonstrated on the case study of a 60-story FCT structure. It is observed to be superior to the case of randomly-generated initial samples and practically applicable for the seismic optimization of super high-rise FCT structures.