This paper evaluates the effect of Structure-Soil-Structure Interaction (SSSI) between two buildings under seismic excitation given different parameters of the buildings, inter-building spacing, and soil type. An extended simplified reduced-order model, that enables higher mode interaction between structures, is proposed. This enables the exploration of the interaction between buildings with a very large difference in height. A database of strong ground motions records with Far-Field, Near-Field Without Pulse and Near-Field Pulse-Like characteristics are employed. Over 3 million system/ground motion cases are analysed in this extensive parametric study. The results suggest that the extended model captures significant interactions, in displacement responses, for the cases of a small building closely flanked by a much taller one.
During an earthquake, civil structures interact with the surrounding soil beneath their foundations. These structures are typically analysed (dynamically) as singleton structures, i.e. without any consideration of their neighbouring structures. This phenomenon is widely known as Soil-Structure Interaction (SSI), and the importance of including its beneficial or adverse structural effects has been the focus of attention for more than 40 years. Nevertheless, the existence of a high density of buildings in large cities inevitably results in the possibility of seismic interaction of adjacent buildings through the underlying soil. This problem is better known as Structure-Soil-Structure Interaction (SSSI) and has received more attention in recent years. The pioneering works of Luco and Contesse , Kobori et al. , Lee and Wesley , Murakami and Luco , Wong and Trifunac , Lysmer et al. , and Roesset and Gonzales  have emphasized the complexity of the problem and have investigated the importance of considering the dynamic coupling between several structures. Some early experimental studies at real or small scaled conducted by Mattiesen and MacCalden , and Koroby et al.  have also captured the SSSI effects. More recent investigations have been developed based on numerical two or three-dimensional Finite Element Method (FEM), Boundary Elements Method (BEM) or a combination of these two FEM/BEM procedures. For example, the works of Qian and Beskos , Betti , Karabalis and Huang , Karabalis and Mohammadi , Lehmann and Antes , Qian et al. , Bard et al. , Yahyai et al. , Padron et al. , Bolisetti and Whittaker , among others. These studies have identified key factors that control the seismic interaction behaviour such as: (i) the inter-building distance, (ii) the direction of the alignment between foundations, (iii) the relative height and dynamic characteristics of adjacent buildings, (iv) the aspect ratio (the building height to width ratio), and (v) the soil class. Discrete soil/foundation-spring models have been successfully applied in the evaluation of SSSI problems, where Mulliken and Karabalis [20,21] calculated the interaction between adjacent two and three identical rigid surface foundations supported by a homogeneous halfspace soil, and subjected to impulsive, moment, sinusoidal and random loads. Recently, Alexander et al.  proposed a set of rotational springs to model the interaction between adjacent closely spaced buildings. These models were validated using finite element analyses. Aldaikh et al. [23,28] and Knappett et al.  extended the validation of these proposed interaction-spring models with both physical shake table and centrifuge tests. Additionally, Aldaikh et al.  proposed an alternative closed-form analytical expression for these interaction springs based on a Boussinesq approximation of the surficial displacement fields. These alternative formulae where shown to be completely consistent with those initially proposed and validated in [22,23,28]. Vicencio and Alexander  extended these previous models further by permitting the soil to exhibit nonlinear hysteretic behaviour. Results indicate that SSSI effects can increase with soil nonlinearity