A first level vulnerability assessment of buildings on a flood-risk area

Floods are natural phenomena with a catastrophic impact on the communities. Buildings are in many cases highly exposed to such events that produce different grades of damage and collapses. When structures are located in areas characterized by high levels of exposure to potentially disastrous flood events, methods for the territorial analysis of their vulnerability would be necessary. The Authors propose a method for estimating the vulnerability of buildings to floods. The proposed strategy is attributable to the methods of estimating the Vulnerability Index (VI), widely used in the analysis of other types of risks, such as seismic, volcanic, climate change. It proposes a linear combination of scores assigned to a some structural features that play a significant role during the flood.

Through the VI, the proposed method provides the most probable Damage Level (DL) for an assigned intensity of the event described by the flow velocity and height. The damage scale changes from 0, which means no damage, to 100 which represents a structural collapse.

The method is calibrated on the results of numerical simulations, carried out on a large population of randomly generated structures. The numerical simulations are first employed to detect the significant parameters by evaluating their sensitivity on the structural resistance. For each selected parameter, intervals are identified to assign a vulnerability class variable from high vulnerability (A) to low vulnerability (D) and a corresponding score. Subsequently, the best fit between the DL estimated by the proposed method and that evaluated through the numerical simulations is found.

The resulting method defines a rapid tool to estimate the DL of a building on the basis of few structural features easily obtained by an external survey. A case-study is proposed to assess the feasibility of the proposed approach. Results have highlighted how many buildings and many event scenarios can be analyzed in short time to produce risk maps for emergency plans and to set up wise vulnerability reduction strategies.

The proposed method, in its present form limited to masonry and reinforced concrete structures, can be readily extended to other typologies and its accuracy can be further increased by combining the results from observed damages.