Synthetic Seismic Design Strategy of Building Structures in Urban Area

Abstract eng:
Cities are syntheses of many individual buildings and infrastructures that support the function of the built environment. Current seismic design strategies focus on individual buildings, including the safety of their occupants, operation of the business they host, and the economic loss they may bring about to their owners if they are damaged during earthquakes. In such strategies, life safety is always the most important performance target than other concerns such as continuous operation and economic loss. This makes people tend to underestimate or even overlook the importance of the latter performance requirements. In big cities, earthquake damage to so many of the buildings at the same time may cause disasters for people who live in the cities, even if the extent of damage to each building is acceptable per the current seismic design codes for buildings. Seismic design of buildings in urban areas should not focus only on individual buildings themselves. Instead, the seismic performance target of individual buildings should conform to the performance target of the city. In this paper, the shortcoming of ductility-based seismic design strategy is first discussed from the viewpoint of demolition of damaged buildings. The important differences between individual buildings and cities are summarized in terms of their spatial scales and life spans. It is because of the huge spatial scales of modern cities that the discontinuity of their functions may make the cities unsuitable for people to live after major earthquakes, even if not a single building collapsed and caused direct fatality. Therefore, seismic damage control for functionality becomes a critical concern for the sake of cities, especially if the cities are too big to fail, such as Tokyo, Beijing and Los Angeles. It is because of the long life spans of cities that major earthquakes would sooner or later strike the city during its life span. Its buildings should therefore be seismically designed to remain functional under very rare earthquakes, which is compatible to the life span of the city rather than the buildings themselves. Several techniques among many others for seismic damage control are recommended at the end of the paper. These techniques have proved to be effective in protecting not only the safety, but also the functionality of buildings under major earthquakes.

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