The effects of earthquake induced pounding on the nonlinear response of torsionally coupled buildings resting on flexible soil are investigated in the current study. Three steel moment-resisting frame buildings with the same symmetric plan having 4, 7 and 10 stories are considered. Three-dimensional nonlinear models with different eccentricity ratios are created. The soil-structure interaction phenomenon is taken into account using the Winkler beam on nonlinear springs. The pair of adjacent structures spaced at different clear distances resting on a flexible soil are analyzed under a consistent set of ground motion records and the effects of seismic pounding, torsional eccentricity and soil-structure interaction are studied by comparison of nonlinear dynamic responses of buildings. The results show that the peripheral frames experienced the most critical conditions during earthquake-induced pounding and the combined effect of soil-structure interaction, torsional eccentricity and pounding results in the most severe nonlinear responses of the studied buildings in certain cases.

Introduction

Adjacent buildings may experience seismic pounding during strong ground motions leading to impulse force being imposed on these structures. Such an extra force can alter the design forces and performance level of structures. As the seismic pounding phenomenon is substantially complicated, the building codes just set a seismic separation distance provision to completely avoid occurrence of pounding. Many efforts have been made to clarify various aspects of the earthquake-induced impact between adjacent structures. A part of these works was devoted to develop different linear and non-linear models to simulate seismic pounding [1]. The non-linear viscoelastic model proposed by Jankowski [2] and a Hertz contact model with nonlinear damping developed by Muthukumar and Desroches [3], for instance, are the results of these researches. Soil-structure interaction and torsional eccentricity are important factors which may impress seismic response of neighboring buildings. The soil-structure interaction effect arises from transferring seismic waves between adjacent foundations which is called structure-soilstructure interaction, or SSSI. Reviewing the literature shows that oneor two-dimensional models without including torsional response and soil-structure interaction have been mainly utilized to investigate seismic pounding response of adjacent structures.