### Abstract

In order to appropriately determine the seismic response of a structure founded on soft soil, it is important to understand the effects of soil structure interaction (SSI) on the vibrational input to the structure. In the near field, the vibrations of structures may modify the free-field ground accelerations and hence the

resulting input motion to the structure at foundation level. This is expected to be especially true for urbanized areas where the effects of multiple adjacent structures will be superposed. This paper presents the results of two-dimensional finite element analyses to investigate the effect of both a single structure and multiple adjacent structures, founded on soft soil, in modifying the structural input motion at foundation level and the resulting seismic performance of the superstructure. The structures are modeled as simple single degree of freedom oscillators with dynamic properties representative of low-rise constructions and founded on shallow raft foundations. It is demonstrated that the effects of SSI on soft soil, which increase the magnitude of the accelerations beneath the structure may be improved or worsened with additional surrounding structures. It is further shown that for a symmetrical problem (i.e. identical adjacent structures and symmetrical harmonic ground motion), the co-seismic performance of the superstructure is worsened for the case of adjacent structures, and this effect is stronger as the interbuilding spacing is reduced. The post-earthquake (permanent) response of the structures is also shown to

be highly asymmetric and non-negligible, meaning that linear elastic soil models are inappropriate for seismic response analysis within heavily urbanized areas.

resulting input motion to the structure at foundation level. This is expected to be especially true for urbanized areas where the effects of multiple adjacent structures will be superposed. This paper presents the results of two-dimensional finite element analyses to investigate the effect of both a single structure and multiple adjacent structures, founded on soft soil, in modifying the structural input motion at foundation level and the resulting seismic performance of the superstructure. The structures are modeled as simple single degree of freedom oscillators with dynamic properties representative of low-rise constructions and founded on shallow raft foundations. It is demonstrated that the effects of SSI on soft soil, which increase the magnitude of the accelerations beneath the structure may be improved or worsened with additional surrounding structures. It is further shown that for a symmetrical problem (i.e. identical adjacent structures and symmetrical harmonic ground motion), the co-seismic performance of the superstructure is worsened for the case of adjacent structures, and this effect is stronger as the interbuilding spacing is reduced. The post-earthquake (permanent) response of the structures is also shown to

be highly asymmetric and non-negligible, meaning that linear elastic soil models are inappropriate for seismic response analysis within heavily urbanized areas.

Original language | English |
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Title of host publication | 5ICEGE - Proceedings of the 5th International Conference on Earthquake Geotechnical Engineering |

Place of Publication | Santiago, Chile |

Publication status | Published - 2011 |

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## Cite this

Knappett, J., Stropios, E., Kaponis, C., & Yakub, H. (2011). Modification of ground and structural response due to seismic structure-soil-structure interaction. In

*5ICEGE - Proceedings of the 5th International Conference on Earthquake Geotechnical Engineering*http://www.sochige.cl/download/9.2.MOGKN.pdf