New Building Damage Assessment Method Based on Numerical Tsunami Simulation and Analytical Force Estimation: Case study of the 2011 Tohoku tsunami

Abstract

 Macro scale assessment of building damage by tsunami can be performed using two classical methods namely, fragility functions and weight factors based on their vulnerability. However, these methods do not consider the actual performance nor strength of the buildings and damage might occur before either of flow depth and flow velocity reach maximum values. This study aims to investigate if instead analytical force estimation of tsunami forces and building strength is able to predict building damage. About 20,000 damaged wooden buildings data in Ishinomaki City from the 2011 Great East Japan tsunami were used for this analytical experiment. The impact of floating debris was also added based on weight. Building strength from bearing wall is estimated from building design standard which is mainly based on floor area and building height. Resistance reduction coefficient was also added for aged buildings. Two damage (collapse) patterns (washed away and destroyed) were analytically assessed using sliding and overturning mechanisms. As results, it was found the proposed method could reproduce the actual damage condition with very high accuracy for both collapse patterns. Almost destroyed and washed away buildings occurred when the flow velocity is higher than 2 m/s regardless of flow depth. Besides, it was found using the maximum flow depth and flow velocity could underestimate the damage by up to 2-4 times. This new method will be useful for building damage assessment in areas that have no actual tsunami damage experience.