In conventional seismic design, the structure is often assumed to be fixed at the base. However, this assumption does not reflect reality. Furthermore, if the structure has close neighbors, the adjacent structures will alter the response of the structure considered. Investigations on soil–structure interaction and structure–soil–structure interaction have been performed mainly using numerical models. The present work addresses the dynamic response of adjacent single-degree-of-freedom models on a laminar box filled with sand. Impulse loads and simulated ground motions were applied. The standalone condition was also studied as a reference case. Models with different fundamental frequencies and slenderness were considered. Results from the impulse tests showed that the top displacement of the models with an adjacent structure was reduced compared with that of the standalone case. Changes in the fundamental frequency of the models due to the presence of an adjacent model were also observed. Results from ground motions showed amplification of the maximum acceleration and the top displacement of the models when both structures have a similar fundamental frequency.
The influence of soil on the dynamic response of soil-structure systems is usually studied on a stand-alone (SA) structure, even though closely adjacent structures form the vast majority of the population, especially in large cities. When structures are closely adjacent to each other, the wavefield in the soil, generated by the vibration of the footings, produces a complex interaction between them. Scant attention, especially by physical experiments, has been paid to this interaction. This work addresses the seismic response of a single degree-of-freedom structure (structure of focus) considering the influence of one and two closely adjacent neighbours. Experiments were performed using a large laminar box filled with sand sitting on a shake table. Results from utilising four recorded ground motions from the 2010-2011 Canterbury earthquake sequence are analysed. The effect of adjacent structures on the acceleration and displacement of the top mass of each structure, as well as the uplift of the footings, are discussed. Changes in the fundamental frequency due to the presence of neighbouring structures are identified. The use of the SA system, without consideration of closely adjacent structures, may result in a significant error in the estimation of the response of the structure of focus. In general, acceleration, lateral displacement and uplift reduced in comparison with that of the corresponding SA case. A footing settlement mechanism, resulting from uplift of the system that reflects the influence of adjacent structures, is also revealed.
Most of the experimental works on adjacent structures consider a short distance between them to analyze the interaction. Additionally, the majority of these studies focus on changes in the dynamic response of the buildings (e.g. acceleration, lateral displacement, or rocking) assuming that the fundamental frequency and the damping of the structures remain the same as those for the stand-alone case. This work intends to reveal the effect of distance on the interaction between adjacent structures and the effect of neighboring buildings on the dynamic properties of a structure. This was achieved by studying the dynamic response of single degree-of-freedom (SDOF) structures in a laminar box filled with sand sitting on a shake table. This study initially addressed the attenuation of the acceleration through the soil with the distance considering the structures at different distances. The second part of the study considers multiple configurations of adjacent structures to estimate the influence of the number of neighbors on the fundamental frequency and damping ratio of a subject building. An increasing fundamental frequency with an increasing number of participating structures was observed. An equation to estimate the influence of the number of neighboring buildings on the fundamental frequency of the subject structure is proposed. For the damping ratio, a considerable influence of the soil was observed. The lowest damping was obtained for an intermediate number of structures.
The seismic design of structures generally considers a fixed base assumption, thus neglecting interaction with the supporting soil. The main structural property considered is usually the fundamental period. However, when the influence of soil-foundation-structure interaction (SFSI) is taken into account, other parameters such as structural slenderness, may play an important role in the response. Current design codes, (e.g. FEMA-440 and FEMA-450), assume that SFSI always has beneficial effects in the form of a reduction in the fundamental period spectral acceleration or base shear. This assumption has been studied and discussed by several authors. Additionally, in major urban areas structures are generally closely adjacent, and this situation is more complex than that of a structure whose response may be considered independent of all others. This study sets-out to improve the understanding of the behaviour of a clustered structure-soil-structure system. A 2D numerical model is used to simulate the behaviour of single and multiple structures on sand considering a range of slenderness ratios. Linear single degree-of-freedom (SDOF) structures and nonlinear soil are considered. The role of key parameters, e.g. effective building period and slenderness ratio of the structure-foundation system, will be elucidated.
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