آنالیز اثر استراتژیک مقاوم سازی لرزه ای در مقیاس بزرگ با استفاده از آسیب پذیری ساختمان های سنگی قدیمی Analysis of the impact of large scale seismic retrofi tting strategies through the application of a vulnerability-based approach on traditional masonry buildings

1 Introduction and scope Risks are associated to dangerous events that have an estimable probability of occurring and some potentially severe consequences. In the case of earthquake risk, it is a compound concept determined by the combination of the local seismic hazard, exposure and intrinsic vulnerability of either a singular structure or a building stock. From an engineering point of view, risk mitigation is generally concerned in reducing the structural vulnerability through the implementation of seismic retrofi tting strategies, within a cost-effectiveness framework. For management purposes, it is recognised that earthquake risk requires a multidisciplinary evaluation that must take into account the expected physical damage, the number of casualties and economic losses. These risk analyses outputs have to improve decisions in order to contribute to the effectiveness of risk management, concerning the action and identifying the weakness of the exposed element and their evaluation in time (Carreño et al., 2007). Thus, the comprehensive seismic vulnerability assessment of an old urban centre, with the view to mitigate earthquake risk, assumes great importance due to the evident potential of physical, human, economical and patrimonial losses associated to such areas. In this context, this paper addresses the topic of the seismic retrofi tting of traditional masonry buildings in urban environment through a vulnerability-based approach from which a series of vulnerability, loss and economic outputs are critically discussed. In order to improve their interpretation, the results are mapped using a commercial GIS software, ArcGis® 10.2 (2012), wherein geo-referenced graphical information was combined and connected to a relational database containing the main structural characteristics of the assessed buildings. Various modules with different objectives were developed and integrated into the GIS, including vulnerability assessment, damage and loss estimation (number of collapsed buildings, casualty rate, number of unusable buildings and repair costs) for different macroseismic intensities, allowing for the construction of multiple physical damage and loss scenarios. With this discussion, the authors intend to demonstrate how vulnerability index methods can be used to analyse the impacts resulting from the implementation of large scale retrofi tting programs and to give a contribution to clarify the common idea that seismic retrofi tting interventions are not viable from an economic point of view, particularly in Portugal wherein these kind of interventions to reduce the seismic vulnerability of old building stock have been neglected as inherent to rehabilitation and retrofi tting actions during the last decades.