Vertical evacuation buildings: Sequential earthquake and tsunami assestment

Large earthquakes can generate tsunamis that affect cities located in coastal areas, and the most common strategy to reduce fatalities in these cases is to develop horizontal evacuations to sectors that are high and safe. However, in some cases, due to the topology and topography of the cities, the time needed to reach these safe places is too high. Thus, the vertical evacuation to buildings arises as an alternative, which can reduce significantly the evacuation time. For example, in the case of the city of Viña del Mar, in Chile, recent studies show that in the case of an extreme event, 38% of the population is not able to reach safe areas through horizontal evacuation, therefore, the vertical evacuation is an alternative that should be considered.

Vertical evacuation refuges have been considered and implemented in different countries, mainly in Japan, United States and Indonesia, with different typologies: (1) buildings specially constructed as vertical evacuation refuges (towers, buildings or elevated platforms above the expected level of flooding); (2) previously existing buildings, modified or adapted to improve their use for vertical evacuation; and (3) berms or artificial hills. Although there are current regulations in the world that allow the design of vertical evacuation shelters, research on the expected performance of these types of structures under multi-hazard scenarios is scarce. Few studies are available regarding the expected performance of buildings under the sequential seismic-tsunami actions, and even fewer studies consider the scenario in which the building is simultaneously used as a vertical refuge, concentrating large amounts of mass in some area of the building, in case of a strong aftershock.

Thus, the objective of this research is to analyze an existing building in Chile that can serve as a refuge for vertical evacuation. An evaluation of the performance of the structure is carried out by means of a non-linear model that incorporates the reduction of the capacity of the building through a plastic-hinge model based on the smooth histerical model (SHM) considering the sequential earthquake-tsunami action and considering simultaneously that the building is used as a refuge. Results of this research support the vertical evacuation as an alternative to mitigate the effects of a tsunami in Chilean coastal cities.