Structural Design of Sea Gates against Tsunami Loads considering Ultimate Strength

Abstract

A series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake is termed as a Tsunami or a tidal wave or a seismic sea wave. It is normally triggered by the factors like volcanic eruptions, earthquake, underwater explosions, landslides, glacier calving, meteorite explosions etc. The wavelength of the Tsunami waves is much larger when compared to the normal sea waves. Unlike the normal sea waves which appear as a breaking wave, tsunamis appear initially like a rapidly rising tide comprising of a series of waves, with their periods ranging from minutes to hours. Japan is a country known for its record history of Tsunamis. The Great East Japan earthquake off the Pacific coast of Tohoku, 2011 with a magnitude of 9-9.1(Mw) initiated some influential tsunami waves that stretched elevations of up to 40.5 metres (133 ft.) in Miyako in Tōhoku's Iwate Prefecture and which travelled up to 10 km inland , in the Sendai area. The death counts recorded were around 15,896 along with destruction to nuclear power plants, roads, railways, buildings etc. It was declared as the costliest natural disaster in history with the estimated economic cost of US$235 billion by the World Bank. Based on the studies conducted by the joint Tsunami survey teams under the main survey group, as an aftermath of the 2011 Tohoku Tsunami, many conclusions were implemented on the characteristics of the tsunami wave. The unrivalled scale and the low frequency of occurrence are believed to have led to the complex behaviour of the wave. The performance of the Tsunami counter measures available then, before the tsunami were evaluated based on the survey and other experiments numerical analyses. This actually paved the way for the understanding of the limitations of the countermeasures used till then and made the government think of new possible ideas/technologies that could be implemented in future for better protection.