Seismic risk assessment at the urban scale through the development of fragility curves: the case of Chlef City (formerly El Asnam), Algeria

The seismic vulnerability of a building stock can be assessed by developing fragility curves, thereby creating a portfolio. These curves are a commonly used tool in seismic studies. Given its historical seismicity, Chlef City, located in northern Algeria, requires such an evaluation. Consequently, aiming to assess the buildings' seismic vulnerability at Chlef city's scale, this study categorizes the city's building stock into different typologies. A total of 33,717 houses within 22,053 buildings are considered. This stock is classified into seven typologies, based on three criteria: (1) the seismic code level; (2) the construction material and structural system (massive masonry, RC moment frames with brick infill, reinforced concrete, and RC dual systems); and (3) the building's purpose (residential/facility). The fragility curves were developed using the Vulnerability Index Method (VIM) of the RISK-UE methodology, which requires the seismic action to be defined in terms of macroseismic intensity. In this study, the European Macroseismic Scale <italic>EMS-98</italic> is used. Therefore, the seismic intensity of the 1980 El Asnam earthquake (<italic>IX</italic>−<italic>X</italic>) is considered. The study's findings reveal that the massive stone and the regularly brick-infilled walls typologies, encompassing 8,242 buildings in total, are the most vulnerable and represent a rehabilitation priority. Two other typologies, covering 4,082 buildings, fall in the second range and are moderately vulnerable. Thus, together these four typologies represent 55.88% of the city's building stock. The study outcomes represent a valuable tool for local urban authorities, enabling them to prioritize the rehabilitation of the urban stock in this seismically prone city.