Multi-criteria decision support framework for optimal multi-hazard design of passively damped structures
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This dissertation develops a new multi-criteria decision support framework for conducting multi-hazard design and retrofit of seismic- and wind-excited structures with passive energy dissipation (PED) devices. In addition to designing in compliance with the relevant codes of practice, it is important to note that the performance of PED devices for reducing the structural responses depends on the type, size, and distribution of dampers. The proposed framework provides a genetic algorithm (GA) based methodology to address these optimization issues of structural control systems within the context of nonlinear structures. Steel buckling restrained braces, viscous fluid dampers and solid viscoelastic dampers are all considered as possible design alternatives within this framework. In the proposed algorithm, passively damped structural designs evolve toward configurations that limit damage associated with inter-story drift and absolute peak floor acceleration, while considering essential conflicts in dynamic response demands of the structures under different hazard environments, involving earthquakes and strong windstorms. Optimal design of passively damped structures in such uncertain hazardous environments requires not only choosing the most cost-effective approach from a series of alternatives but also defining project-specific constraints and the risk associated with each decision alternative. Thus, unlike previous work in PED optimization, the proposed framework introduces a newly developed multi-objective genetic algorithm to accelerate the convergence to the robust design solutions and to maximize the overall benefit of the structural control system. Additionally, a probability-based optimization approach is introduced to allow decision makers to achieve a specific performance objective, such as identifying the retrofitting investments that will result in minimum life-cycle cost impact on a building. This new approach uses weighted life-cycle cost as an objective function to permit consideration of risk aversion by accounting for uncertainty related to earthquake frequency, structural vulnerability, cost of structural damage and retrofitting, and mitigation benefits. The proposed optimization framework is applied to several example buildings designed or retrofitted with passive control devices to demonstrate the effectiveness of the optimization approaches. From the illustrative examples, it is positively concluded that the modular framework can be successfully used as a practical decision-making tool for cost-effective optimal multiple hazard design of passively damped structures. Also, it is shown that the probability-based optimization approach results in design or retrofit alternatives that combine well with the performance-based design concept, with usage of more realistic design criteria, such as expected life-cycle cost of meeting prescribed performance level.