Multi-performance design of dissipative bracing systems through intervention cost optimization

In recent years, the need of retrofit interventions on existing buildings is increasing, also due to the high economic losses recorded after the recent seismic events. The intervention techniques based on stiffening and energy dissipation are one of the most widespread among the several available. Despite the great diffusion of this kind of interventions, there are still no clear and shared rules about design principles and, above all, about the performance objectives to be followed within the design. In particular, there is a lack of design approaches based on optimization of intervention costs and cost-benefit assessment. This paper concerns the optimal design of dissipative braces for seismic retrofitting of existing reinforced concrete buildings in the context of a multi performance design problem. Topological and dimensional optimization of the braces is achieved by minimizing the real intervention cost through an innovative formulation of the objective function. The procedure is based on elastic linear analyses, keeping in count the inelastic behavior of dissipative devices and concrete frame through linear equivalent schemes. The reliability of such linearized schemes is discussed by a comparison with structural response obtained with Non-Linear dynamic analyses on a case study structure. Further, it will be shown how the procedure allows, besides the design of the braces characteristics, a critical assessment and choice of the performance levels in order to optimize the cost benefit ratio of the intervention, thus showing its effectiveness as decision-making tool for seismic risk mitigation.