Physical vulnerability models for assessing building damage by debris flows

A catastrophic debris flow occurred in Zhouqu County, Gansu Province, Northwestern China, at midnight on 7 August 2010, resulting in damage to > 390 buildings. Assessment of the vulnerability of buildings to debris flow hazards is essential to quantify the risk of debris flows. This paper presents a new family of physical vulnerability curves to assess the damage to buildings by debris flows based on extensive observed data of building damage and simulated debris flow intensity. A database of damaged buildings in the affected area of the Zhouqu debris flow was reconstructed. Numerical simulations using FLO-2D were conducted to determine the intensity of debris flows. A series of physical vulnerability empirical models for assessing the building damage has been proposed using various hazard intensity measures. Since buildings of different structural types have different resistances to debris flows, the vulnerability functions were developed for two typical types of structures, i.e. brick-concrete structures and reinforced concrete-frame structures. The proposed vulnerability functions are comparable with those for debris flows in Switzerland, Italy and Austria. The buildings may be completely destroyed when the debris flow depth is more than one half of the building height for both types of building structures