Tsunami Force on Elevated Buildings

Abstract: Tsunami is a natural hazard that frequently hit Indonesia. Statistic indicates that the frequency of tsunami occurrence in Indonesia increased sharply during the last two decades. This phenomenon should be anticipated fully as many Indonesian cities or towns are located close to the shore line which may be prone to tsunami attack. Tsunami force on building can be much larger than the hydrostatic force due to inundation and depend largely on the tsunami surge speed. Existing studies suggest that tsunami force on a vertical wall varies from as small as 1.4 times of the hydraulic force to more than 10 times of the hydrostatic force of water depth equal to the tsunami surge height. Such force is larger than a normal building can withstand. Hence, it might be appropriate to elevate building especially near the coastline to reduce tsunami forces against them. Research on tsunami force on elevated buildings was carried out in a flume of 1.45m width. The building was represented by a small box of 20cm x 20cm x 20cm. The height of the floor from the ground was varied from zero to 6cm. Based on a model scale of 1:100, the maximum height of the elevated floor was approximately 6m or approximately a half of the tsunami surge height of Aceh in December 2004. The simulation was conducted at Hydraulic and Hydrology laboratory, Research Center for Engineering Science Gadjah Mada University Indonesia. The result shows that there is a significant reduction of tsunami force on elevated buildings. Force reduction depends on the ratio between tsunami surge height (h) and elevation of the floor above the ground level (he). A simple equation is proposed to calculate tsunami force on elevated buildings. Keywords: Tsunami force, elevated building, porosity, simulatio