Selection of the "best" seismic upgrading solution for a RC building by MCDM

Multi-Criteria Decision Making (MCDM) is made of stepwise procedures useful for complex problems allowing to rank the overall performances of a finite set of alternatives in respect to certain criteria of interest. They help the Decision Maker (DM) to identify the ‘best’ feasible solution which is defined as the one which more closely matches all the relevant goals. MCDM is common in several fields such as resources allocation planning, medical treatment choices, natural resources’ management. This paper presents an application of this methodological framework to the seismic retrofit of an under-designed RC structure. In fact, several traditional, as well as innovative, upgrade strategies are available for the achievement of the retrofitting goals, each of those scoring different points in respect of different criteria such as installation and maintenance costs, required application time, performances, durability and invasivity. The selection of the most suitable solution depends on the peculiarities of the case under exam and is, often, not straightforward. Due to the several noncommensurable and conflicting criteria, generally there is no solution satisfying all of them simultaneously [1] calling for MCDM. The TOPSIS method [2] is considered being one of the most widely adopted. The eigenvalue approach [3] is used, instead, to express the relative importance (weights) of the criteria. The application is described in detail; it refers to a three-storeys, irregular, pre-code RC structure built and tested at the European Laboratory for Structural Assessment (ELSA) of the Joint Research Center (JRC) in Ispra, Italy, for the EU project SPEAR [4]. The building is assumed to be located in Pomigliano d’Arco (Naples, Italy) which has been classified as a seismic zone only in 2003 (peak ground acceleration 0.25g) and hence the upgrading needs are actually strongly felt. For this structure three different retrofitting alternatives, improving the seismic capacity by three different structural performance objectives, were designed: (a) columns’ confinement by Glass Fiber Reinforced Plastics (GFRP); (b) steel bracing; (c) concrete jacketing of columns. The considered criteria are technical and social/economical. The destination of the building is chosen to be residential and the DM is assumed to be the owner.