Correlation of fragility curves for vernacular building types: Houses in Lalitpur, Nepal and in Istanbul, Turkey

Traditional urban housing in developing countries has been substantially eroded in the past 20 years, owing to supposedly better and safer housing conditions offered by new typologies, such as concrete frame apartment blocks. The vernacular historic buildings fall prays not only of socio-economic advancement, but also of the lack of proprietary analytical models, that professionals can reliably use to evaluate the actual safety of these buildings with respect to seismic hazard. This phenomenon is common to many countries worldwide, notwithstanding the evidence of time, i.e. the fact that the building type might have survived many destructive events in the past. The paper proposes a critical analysis of few vernacular construction types in regions of high and medium seismicity, highlighting how specific structural details are included in the construction process to better qualify their behavior against earthquakes. It then shows the application of a numerical procedure to evaluate the vulnerability of such buildings to two typologies, one common to the Katmandu Valley, Nepal and the other found in the historic districts of Istanbul. On the basis of the vulnerability analysis carried out on samples of 50 buildings for each case, fragility curves for each typology are derived and compared to typical fragility curves for modern construction.