Parametric Studies on Overturning Moment Ratio of Buildings with Shallow Foundation for Tsunami Loading

As reported in literature number of buildings including five reinforced concrete and one steel framed buildings in the town of Onagawa and two buildings in the city of Miyako have failed by overturning during past 2011 Gear East Japan Tsunami. During Tsunami, exceedance of the instantaneous overturning moment due to buoyancy force and hydrodynamic force above the resisting moment due to self-weight of the building has been found to cause the overturning failure of building. In the present study, residual air space ratio (C_b), inundation depth (R) and height of the building (h) are identified as important parameters which influence the action of overturning. Residual air space ratio is defined in such a way that C_b equal to 1 means no water enters into building and C_b equal to 0 represents entire building is filled with water. The variation of overturning ratio of building w.r.t. the identified parameters are studied for four inundation depths, five heights of building and five air void ratios for the chosen 8mx8m plan of building. From the limited studies made, it is observed that when C_b is equal to 1 i.e. when no water enters the building, there is a maximum possibility for overturning. O_R is found to increase linearly with C_b. Similarly, when the inundation depth is more, there is a maximum possibility of overturning of building, however the variation of O_R with R is not linear. Based on the parametric study a model has been proposed for calculation of overturning ratio.