A Framework for multi-hazard design and retrofit of passively damped structures

Multi-hazard consideration is gaining importance within the design and retrofit process of many important structures. The primary benefits for multi-hazard approaches to the structural engineer include: (1) identification of the mitigation alternatives that address either single or multiple hazards, and (2) optimization of these hazard mitigation strategies. However, this recent popularity of a unified multi-hazard approach for design or retrofit of structures could be attributed to the high cost of the required mitigation strategies compared to retrofit of the structure for a single hazard and the limited information on life-cycle cost. Thus, a conceptual framework is required for rational comparison of hazard mitigation strategies for structures experiencing multiple environmental hazards, incorporating life-cycle cost assessment. This paper presents a computational methodology for the optimal life-cycle cost of seismic and wind-excited structures retrofitted with passive energy dissipation devices such as metallic yielding dampers, viscous fluid dampers, and viscoelastic solid dampers. In addition to designing in agreement with the relevant codes of practice, it is important in design or retrofit of structures to consider that the performance of passive energy dissipation devices for reducing the structural responses depends on the distribution, type, size, and number of dampers in the structure. The proposed computational framework integrates a genetic algorithm (GA) based methodology to address these optimization issues of multi-hazard design within the context of nonlinear steel frame structures. Optimization objectives in this framework include minimizing both the damage to and life-cycle cost of a structure, which is vulnerable to one or two of the main natural hazards: earthquakes and strong wind loads. While considering the essential conflicts in dynamic response demands of the structures to these two natural phenomena, passively damped structural designs evolve toward configurations that satisfy prescribed constraints. Monte Carlo simulation models are generated to evaluate various retrofit strategies with different damage levels possible over the life-cycle. The life-cycle cost associated with each scenario is computed, with a discount factor, to obtain the optimum life-cycle cost for various retrofit strategies. The specifics of the computational framework are illustrated through example case studies to highlight the potential benefits of the proposed computational multi-hazard design approach.