A procedure for the identification of the seismic vulnerability at territorial scale. Application to the Casbah of Algiers

One of the objectives of the PERPETUATE EU-FP7 project was to determine a sound approach to the quantification of the seismic vulnerability of historic centres at territorial scale. The procedure presented herein provides a ten steps guideline from how to select building samples in the area of study, to how to compute the buildings’ seismic performance and finally how to evaluate rehabilitation decisions to reduce the seismic fragility of the studied typologies over an entire district or city. The procedure is illustrated in this paper by way of application to The Casbah of Algiers, a world heritage site composed of building clusters from the Ottoman to the French period. Pre-existing seismic damage, decay due to lack of maintenance and environmental factor and a urban irregular and complex lay-out make this application particularly challenging. A total number of around 150 houses, characterised by the most representative features of the Algerian historic construction, have been selected in collaboration with the Directorate of the Office for Management of Cultural Property of the Ministry of Culture,. The seismic Vulnerability Assessment Method (VAM) underpinning the 10-step procedure is is FaMIVE (Failure Mechanism Identification and Vulnerability Evaluation), a mechanical approach based on limit state analysis and kinematics, which allows computing collapse load factor, deriving capacity curves and determining fragility functions. As the approach identifies also the collapse mechanisms, it provides a base for choosing and evaluating the effects of strengthening interventions, which are rolled out at territorial level to improve the seismic performance of the whole sample. The effectiveness of the present procedure for the identification of the seismic vulnerability at territorial scale is discussed in the conclusions.