Seismic fragility assessment of unreinforced masonry churches in central Chile

The present thesis focuses on the seismic fragility assessment of unreinforced masonry (URM) churches in central Chile. The intrinsic value of this built heritage is due to its original features, synthesis of local and European architectural cultures. Due to the structural weaknesses of URM monuments, Chile’s high seismic hazard, the absence of design standards and guidelines, and the ineffective performance of recently implemented retrofits, this built heritage is at-risk. For these reasons, the broad scope of this study is to document, for the first time, an essential part of the heritage asset of Chile, and to highlight principal vulnerabilities through a proper safety assessment framework, with the aim to promote conservation policies compatible with heritage identity and meeting new safety requirements. Historical, typological and technological features of the selected churches, consisting of 106 churches, are outlined and consistent categories are formed. Churches of each class share stylistic and technological characteristics, but also and more importantly, the same structural weaknesses. Within this framework, two scales are adopted to investigate the seismic performance of these monuments: territorial and building. At territorial-scale, the selected 106 churches are organized in a database that collects essential information for fragility assessment and damage forecasting (e.g. expected 2010 Maule PGA, architectural, typological, and material parameters). As a result, the main variables that control the seismic fragility of these structures were determined. The main outcome obtained downstream from this survey is related the damage suffered by the entire stock following the 2010 (8.8Mw) Maule earthquake. The matrix of plots for the frequency distributions of the selected variables and damage level frequency diagrams enabled the identification of the following three homogeneous classes. These are: Colonial (CL), Neo-classical & Variant (NC&V) and Neo-gothic (NG). Probability Mass Functions (PMFs)and Empirical Fragility Curves (EFCs) have been obtained using validated models such as a lognormal distribution fitted by least squares, and a generalized linear model function fitted by maximum likelihood estimation. At building-scale, three case studies representative of fragility classes are identified. These churches are: San Francisco in Santiago, San Judas in Malloa, and San Salvador in Santiago. A methodology to assess the seismic performance of these URM structures is provided, and the seismic response and risk quantified. Finally, a new procedure is proposed to evaluate arbitrary structural retrofit interventions in view of more general ICOMOS principles. For each intervention, a conformity level in terms of alignment with conservation principles has been assessed. This methodology has been applied to evaluate the retrofit interventions proposed or implemented to reinforce the three selected case studies. This thesis provides useful predictive tools for seismic risk reduction plans of churches, which is directly usable as a framework to be employed by stakeholders and safety related decision-makers. Moreover, the main findings can be exported to all those contexts in which European architectural revivalisms have influenced local building techniques (e.g. Central and Southern America).