Decision making tool for seismic retrofit of existing structures based on marginal costs and actualized costs of the retrofitting operations

The loss estimation analysis of a structure subjected to seismic hazard is used to determine the expected costs to be sustained due to seismic damages in the structure life-time. In this work a procedure is developed and applied to an existing structure in L'Aquila, Italy damaged by the April 2009 earthquake, in its as-built and retrofitted configuration. The method consists in a seismic hazard analysis, damage analysis and loss estimation. The loss evaluation is performed considering the probabilistic distribution of construction costs in Italy. The structure is divided into eight assemblies: foundations, external partitions, doors/windows, plumbing system, structural elements elevation, floors, retrofit system. Four limit state for each assembly are considered {very light, light, moderate, severe}. Then, the procedure is reiterated for different increasing retrofitted configurations of the structure, generating increasing initial costs, but a reduction of the expected costs. The results are elaborated in terms of actualized expected costs to face during the lifetime of the structure and marginal cost of the retrofit interventions.