Selection of optimal seismic retrofitting strategy for existing RC building

The selection of the retrofitting strategies has a fundamental technical and social role. Nevertheless, the adopted strategies have often been devoid of objective criteria. Because of the number of buildings that require seismic retrofitting and the reduced economic availability, researchers, professional engineers, and administrators must prepare interventions that represent the best solution to avoid waste. The paper would to introduce some objective tools for professional practice; it highlights several topics (as disruption of use, safety conditions and operational step in construction site) usually neglected in the retrofitting strategies. The retrofitting strategy has been defined through a global vision based on strongly different topics that should be considered. In the paper the main phases of the procedure to define the optimal retrofitting strategy of existing RC buildings are described. The structures under examination were designed and constructed in the ‘80s, in according to the old Italian seismic code. They have showed a general good condition but the assessment has revealed a generalized deficiency of the structures with regard to the required seismic resistance in the new code; thus a retrofitting is necessary. The main design phases have been: (i) structural assessment against seismic and gravity loads, (ii) definition and comparison of some retrofit strategies, (iii) selection of a retrofit strategy based on the results of the structural assessment, architectural and economic considerations, functional strategies defined by owner of the buildings, and quantitative assessment of the workplace health and safety. Different strategies have been considered and compared with Multi Criteria Decision Making (MCDM) in order to select the optimal solution. On the basis the current use of the buildings, the problem of disruption of occupancy has been a fundamental topic. The remarkable importance of the utilization requirements have been considered and particular attention has been devoted to the operational steps.