The seismic performance of existing buildings can be improved significantly through the installation of various retrofit technologies. Decision support systems can be used for the selection of an optimal retrofit alternative when several important decision variables (DVs) need to be considered. Typically, the decision-making process considers a range of economic, social and technical aspects that are of interest to decision-makers; however, less or no consideration is given to the environmental impact (EI) of the retrofit alternatives. This study investigates how including the EI of possible retrofit alternatives as an additional DV in a multi-criteria decision making (MCDM) process can affect the choice of the optimal retrofitting scheme for a reinforced concrete school building in Italy. An assessment methodology for determining the life cycle EIs for the case-study structure, based on environmentally extended input-output life cycle analysis, is described. Then, a set of five retrofit alternatives is developed using response estimates from non-linear static analyses and their performance is assessed using non-linear time-history analysis and the PEER-PBEE framework. Several decision assessments are conducted, using the MCDM framework, each considering a subset of 13 possible DVs, including EI, to select an optimal retrofitting alternative. The results of the MCDM assessment and their implications are discussed in detail. The main conclusions were: (1) in some instances the expected annual EI may be a suitable proxy for the total life cycle EI when used in the MCDM framework; (2) the use of aggregated performance metrics such as the Life Cycle Performance Metric should be carefully considered when the MCDM procedure is used for the decision analysis, and; (3) the most significant factor affecting whether or not the inclusion of EI will affect the choice of optimal alternative is the weights of the DVs assigned by the decision-maker.
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