۱- Introduction

۲- Case studies

۳- Global seismic performance-based assessment

۴- Fragility and loss assessment

۵- Cost-benefit analysis

۶- Final remarks

References

Abstract

This study discusses the cost-benefit analysis resulting from the application of traditional seismic retrofitting strategies on four case studies considered representative of both rural and urban stone masonry building stock of Faial Island, in Azores (Portugal). The seismic performance-based assessment was carried out by applying the N2 Method procedure, and the global seismic capacity of each case study estimated by using a three-dimensional model based on the macroelement approach, which combines both the in-plane and out-of-plane response of masonry buildings, to perform nonlinear static analyses. Fragility and loss estimation was evaluated according to the HAZUS methodology. In general terms, the cost-benefit analysis has demonstrated that the studied retrofitting strategies are indeed capable of reducing substantially the seismic vulnerability of the considered case studies, and also that they represent, in fact, a limited amount of the total replacement cost, not compromising, therefore, their economic viability.

Introduction

The recent upsurge on the revitalisation of historical centres in Portugal, is contributing to the mischaracterisation phenomenon of urban cultural heritage (UCH) assets, as traditional construction techniques and materials are massively being replaced by modern solutions, totally disrupting the aesthetic value of existing assets, and often jeopardising the seismic vulnerability of such assets [1]. One of the preferred arguments used to underpin the phenomenon of both architectural and constructive mischaracterisation is that, allegedly, structural renovation works compliant with existing materials and traditional building techniques are not viable from the economic viewpoint. Another often cited argument is that such traditional materials and building techniques do not comply with the regulatory requirements in force in terms of seismic performance. Hence, and as a follow-up of the research published by Maio et al. [1], the current study aims not only at investigating the authenticity of the arguments mentioned above but also to demystify the generalised idea that traditional strategies for the seismic retrofitting of UCH assets have a significant impact over the total renovation cost. In literature, the term “traditional techniques” usually refers to enhancing measures of the buildings’ structural integrity/stability by using compatible and local materials such as earth and wood, and solutions as ring beams, wooden ties interconnecting parallel walls, corner keys, or the addition of buttresses, for example. However, “traditional” has in this study an additional meaning, in the sense that these strategies are quite common and have been widely applied in the framework of the reconstruction process of Faial island (in Azores, Portugal), after the 1998 Azores earthquake [2]. The validation of the former hypotheses is going to be investigated by assessing the Cost-Benefit Analysis (CBA) of two of these strategies. One of the first cost-benefit models for the seismic retrofitting of buildings was issued by the Federal Emergency Management Agency in 1994 [3,4], which encouraged the development of several studies in this topic ever since [5,6]. In the past few years, several compelling studies within this particular research field have been published, focusing either on residential [7,8] or public-school buildings [9,10]. It is worth noting that despite being widely acknowledged worldwide as a significant decision-supporting tool commonly used for evaluating the efficiency of projects, CBA does not provide an absolute answer about whether or not to undertake the seismic retrofitting of a given asset. This because the decision-making process usually depends on many factors beyond the boundaries of benefit-cost analysis, such as the definition of life safety and post-earthquake performance levels [3].