Tsunami-deck: A new concept of tsunami vertical evacuation system

We introduce the concept of a new type of vertical evacuation shelter. It combines the function of pedestrian bridge and tsunami tower, which are then installed at intersection. The idea provides the ease of constructing and maintenance in addition to the loss of required land acquisition. We first evaluate the performance of pedestrian bridges during the 2011 tsunami in Japan by taking into account the exposure component in term of their position from the shoreline and the susceptibility component in term of the tsunami height around the bridge as the influencing parameters in determining damage probability. We developed fragility curves to show that pedestrian bridges lay on an area less than 500 m from the coastline (around 0.1 of the maximum inundation extent), or in the area where the tsunami flow depth are 1.5 of the height of the bridge’s deck have more than 50 % probability to be damaged by the tsunami. If the function of pedestrian bridge will be expanded into ‘Tsunami-deck’, the information about tsunami behavior at the intersection therefore becomes important. For that reason, we performed a set of numerical experiment of tsunami flow at the intersection to determine conditions that will allow the installation of tsunami-deck with a height similar to the average height of the existing pedestrian bridge. By doing so, we attempted to determine preliminary placement criteria for Tsunami-deck in order to ensure the safety of evacuee. The results gave an opportunity to have more distributed vertical evacuation shelter in flat and densely populated areas.