Keywords: structure-soil-structure interaction, discrete model.

Buildings in urban areas are often surrounded at small and large distances by other structures which may either be similar in design or very different. While it is common practice to determine seismic response of structures in isolation, the high density of buildings in cities inevitably results in the possibility of interaction and coupling of adjacent buildings via the underlying soil. Furthermore, it is less clear how a new construction modifies the dynamics of the existing structure. Can it result in changes in dynamics of this existing building that proves to be less favourable?

An analytical dynamic two-dimensional structure-soil-structure interaction formulation using simple discrete models for structures and soil, and including a rotational spring as a key buildings interaction mechanism is proposed. This system is derived from an energy based approach that leads to a completely non-dimensional low order system. It is shown that even for a relatively simple configuration case, the complexity of the analysis is high due to a large number of system parameters. Various empirical formulae are used to derive an alternative set of system parameters. Finite element analysis is also employed to determine the inter-building stiffness of the elastic medium as no empirical formulae are found in the literature. Following this series of simplifying assumptions, the dynamic problem is conveniently reduced to a meaningful set of four parameters. There are three non-dimensional geometric parameters: (i) building aspect ratio (height / width) (ii) inter-building heigh ratio (height of building two / height of building one) (iii) inter-building distance ratio (inter-building distance / building width) and one material parameter that is a soil class. We consider a generic range of soil properties: loose, medium and dense sand.

The analyses performed are in the frequency domain. We employ a Kanai-Tajimi type seismic event that excites the entire two building-soil system. Wave passage effects are not considered as the buildings are assumed to be relatively closely spaced. In the analysis we consider a general building one that is subject to this seismic event in (a) the presence of a neighbouring building and (b) without any neighbouring building. We show that the total response power of building one can be greatly effected by the presence of building two. We can ask by how much can the total seismic response power of a building one be modified by the presence of a close new building two? Results indicate, from this model, that a large range of ±50% is possible. The larger range seems to occur for less stiff soil.

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