The Town Effect: Dynamic Interaction between a Group of Structures and Waves in the Ground

	The Town Effect: Dynamic Interaction between a Group of Structures and Waves in the Ground Koji Uenishi Research Center for Urban Safety and Security, Kobe University, Kobe, Japan

Summary

In a conventional approach, the mechanical behavior of a structure subjected to seismic or blast waves is treated separately from its surroundings, and in many cases, the dynamic coupling effect between multiple structures and the waves propagating in the ground is disregarded. However, if many structures are built densely in a developed urban area, this dynamic interaction may not become negligible. The first purpose of this contribution is to briefly show the effect of multiple interactions between waves and surface buildings in a town. The analysis is based on a recently developed, fully coupled, rigorous mathematical study, and for simplicity, each building in the town is represented by a rigid foundation, a mass at the top and an elastic spring that connects the foundation and mass. The buildings stand at regular spatial intervals on a linear elastic half-space and are subjected to two-dimensional anti-plane vibrations. It is found that the buildings in this model significantly interact with each other through the elastic ground, and the resonant (eigen) frequencies of the collective system (buildings or town) become lower than that of a single building with the same rigid foundation. This phenomenon may be called the "town effect" or "city effect." Then, second, it is shown that the actual, unique structural damage pattern caused by the 1976 Friuli, Italy, earthquake may better be explained by this "town effect," rather than by investigating the seismic performance of each damaged building individually. The results suggest that it may also be possible to evaluate the physical characteristics of incident seismic/blast waves "inversely" from the damage patterns induced to structures by the waves.

Keywords

Collective behavior, Earthquake hazard, City effect, Town effect, Dynamic interaction.

Related Publications

Uenishi, K. (2010). The Town Effect: Dynamic Interaction between a Group of Structures and Waves in the Ground. Rock Mechanics and Rock Engineering, 43(6), 811-819.
Uenishi, K. (2013). "Unexpected" Failure Patterns and Dynamic Collective Behaviour of an Assembly of Buildings Subjected to Horizontal Impact. Engineering Failure Analysis, 35, 125-132.

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