In historic city centers the mitigation of seismic risk is dependent on the possibility of implementing strengthening programs. Given the cultural and economic value attached to the historic structures, however, interventions should be tailored to suit aesthetic and structural requirements of each building type, and provide sufficient reliability of performance in future earthquakes. A simple analytical model is developed to calculate load factors associated with various collapse mechanisms of wall assemblies, and vulnerability functions are derived. An application shows the capability of the procedure to quantify reduction in vulnerability associated with strengthening implementations for different typologies.

Observations after strong earthquakes show that out-of-plane failure of unreinforced masonry elements probably constitutes the most serious life-safety hazard for this type of construction. Existing unreinforced masonry buildings tend to be more vulnerable than new buildings, not only because they have been designed to little or no seismic loading requirements, but also because connections among load-bearing walls and with horizontal structures are not always adequate. Consequently, several types of mechanisms can be activated due to separation from the rest of the construction. Even when connections are effective, out-of-plane failure can be induced by excessive vertical and/or horizontal slenderness of walls (length/thickness ratio). The awareness of such vulnerability has encouraged research in the field, which is summarized in this article. An outline of past research on force-based and displacement-based assessment is given and their translation into international codes is summarized. Strong and weak points of codified assessment procedures are presented through a comparison with parametric nonlinear dynamic analyses of three recurring out-of-plane mechanisms. The assessment strategies are marked by substantial scatter, which can be reduced through an energy-based assessment

The paper describes the output of a survey carried out in the district of L'Aquila, Italy, in May 2009 after the April earthquake and later in January 2010, and the consequent vulnerability assessment completed by the authors. Observations collected on site regard masonry buildings of the historic centre of L'Aquila and the towns of Paganica and Onna; particular focus was given to a number of buildings of interest, which better represent two locally recurrent building typologies: the mansion and the common dwelling. A description of the main structural features and their influence on damage mechanism is provided, stressing the importance of elements such as wall lay-out, quality of masonry and strengthening interventions. The gathered information is used as input for the application of the FaMIVE method (D'Ayala and Speranza in Earthq Spectra 19 (3): 2003), whereby feasible collapse mechanisms and the associate failure load factors can be identified. The procedure is briefly outlined and results are discussed from the point of view of the performance point: push-over curves produced by statistical elaboration of FaMIVE's output are compared both with the demand spectra obtained from EC8 and the response spectrum for the main shock as recorded by the closest station to the town. Conclusions are drawn on the reliability of the FaMIVE method with respect to its capability of predicting the damage mechanism identified on site.

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Building collapse is the dominant cause of casualties during earthquakes. In order to better predict human fatalities, the U.S. Geological Survey's Prompt Assessment of Global Earthquakes for Response (PAGER) program requires collapse fragility functions for global building types. The collapse fragility is expressed as the probability of collapse at discrete levels of the input hazard defined in terms of macroseismic intensity. This article provides a simple procedure for quantifying collapse fragility using vulnerability criteria based on the European Macroseismic Scale (1998) for selected European building types. In addition, the collapse fragility functions are developed for global building types by fitting the beta distribution to the multiple experts’ estimates for the same building type (obtained from EERI's World Housing Encyclopedia (WHE)-PAGER survey). Finally, using the collapse probability distributions at each shaking intensity level as a prior and field-based collapse-rate observations as likelihood, it is possible to update the collapse fragility functions for global building types using the Bayesian procedure.