Response of Coastal Structures against Earthquake Forces Considering Soil-Structure Interaction and Tsunami Run-Up Forces

The catastrophic tsunamis generated by the great Indonesia earthquake triggered on December 26 th , 2004, warned the coastal community on preparedness and constructing safe structures to resist against such events. Earthquake occurs suddenly without warning and bulk of destruction takes place within a short period of time. Similarly, when tsunami strikes, there will be a tremendous loss and damage in coastal regions. Apart from having a sound warning system in case of tsunamis, it is necessary to build Earthquake–Tsunami Resistant (ETR) shelters, where residents living in coastal plain regions cannot move to farther distances before tsunami arrives the coast. Hence it is necessary to establish analytical methods for obtaining the response of coastal structures subjected to earthquake forces considering soil-structure interaction and also against tsunami run-up forces. A three storied shelter building with four different cases of structural configurations and another typical structure, an elevated water tank of 6 lakh liters capacity are chosen for the analysis. A comparative study is made on the response of these structures against earthquake forces, when they rest on different soil/rock media. In the analysis, IS 1893-2002 seismic code for determining the base shear values against earthquake loads and FEMA 55 to calculate hydrodynamic and impact forces against tsunami impact are used. From the results, it is observed that the refuge shelters that are chosen are more vulnerable to high tide tsunami loads compared to earthquake loads. In general, it is noticed that Base shears and Displacements increase with the decreases in stiffness of the soil and this increase attributes more due to rocking effect of the soil. Buildings with open storey at bottom and upper stories with heavy mass give significant rise to time period of these structures causing early failures during an earthquake before tsunami arrives. In this study, a useful guideline is evaluated demarcating the heights below which earthquake forces and above which tsunami forces are predominant in the structure.