On the dynamic interaction between the ground and a group of structures subjected to seismic disturbances

Abstract eng:
In a conventional approach, the mechanical behaviour of a structure subjected to seismic or blast waves is usually analysed individually, and in many cases, the dynamic coupling effect between structures through the ground is not taken into account. However, if many structures are built densely in a developed area, the dynamic interaction between structures and the ground may not become negligible. The interest in multiple interactions between the ground and structures in an urban environment appeared after the 1985 Michoacan earthquake that had generated severe damage to Mexico City. The difficulties of classical computational methods in matching the seismic records have given the idea that part of the seismic energy transmitted to the buildings may be redistributed in their neighbourhood through multiple interactions between structures and the ground. This phenomenon is called "site-city interaction," and recent simulations based on different models representing a city (or town) and various numerical techniques (Green functions, finite elements, etc.) seem to support this idea. The first purpose of this contribution is to briefly summarise the results of the rigorous theoretical study on a fully-coupled problem of multiple-interaction between the ground and buildings in a town. It will be found that the buildings significantly interact with each other through the ground and the resonant (eigen) frequencies of the collective system (buildings or town) become lower than that of a single building. This phenomenon may be called the "town effect" or "city effect." Then, secondly, from the actual structural damage patterns caused by the 2007 Noto Peninsula, Japan, earthquake, it will be shown that the generation of severe damage in the Doge area of the peninsula may better be explained by the "town effect," rather than by investigating the seismic performance of each damaged building individually. Also, it may be possible to evaluate the physical characteristics of incident waves "inversely" from the damage patterns induced to structures by the waves.

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