Seismic Behavior of Adjacent Structures with Soil-Structure Interaction

During the recent decades, many studies on the seismic response and damage of buildings show the importance of Soil-Structure Interaction effects.On the other side, with urbanization, city blocks contain clusters of closely spaced buildings. Under such circumstances, the dynamic interaction of adjacent structures should not be ignored. However, available evidences show that in the field of soil-structure interaction, little attention has been payed to adjacent structures. In addition, the vast majority of studies are subjected to consider two-dimensional models with plain strain behavior assumptions. Such simplifying assumptions lead to obtain not so accurate and reliable achievements. In this paper, the effects of soil structure interaction and adjacent structures interaction on the seismic response of structures through considering three-dimensional models by using OpenSees software were studied. In this regard, structures are divided in to two major groups, fixed base structures (structures resting on the rigid base) and flexible base structures (superstructures resting on the flexible base), whereas flexible base structures contains Soil-Structures and Structure-Soil-Structure systems. As respects, the common dynamic analysis focus on the fixed base assumptions; therefore, in this study, the evaluations and comparisons between results of flexible base structures and fixed base structures analysis have been paid attention to. Due to the modeling of superstructures for analysis and design processes, three reinforced concrete moment resisting frame, 5, 10 and 15 stories, two spans, resting on shallow foundations with different structural neighborhoods are selected in conjunction with a soil type III (according to ground type classification of Iranian building code), based on the direct method, considering of appropriate lateral boundaries and interfaceelements to simulate frictional contact and probable slip due to seismic excitation. Besides, for the design and analysis of superstructures according to the Iranian concrete code, gravity and lateral loads with considering Iranian national building code part 6 and Iranian seismic code 2800, respectively, is conducted by using ETABS software, then structural sections are designed according to Iranian national building code part 9. Nonlinear dynamic analysis using OpenSeessoftware under influence of three different earthquake records is conducted. The study of the response of acceleration, drift and shear force in the stories indicates that effects of soil-structure and structure-soil-structure interaction depend on dynamic characteristics of buildings, frequency content of seismic data and the height of adjacent structures. The results show that considering adjacent structures with common distance lead to increase or decrease about tens of percent of dynamic responses.Theresults indicate that when a short building (5-story) has two adjacent close tall buildings (15-story), maximum responses of acceleration, drift and shear force increase up to 10, 20 and 40 percent, respectively. Results show that a 10-story building withtwo adjacent 5-story buildings, up to 24% decreases in acceleration response; while with two adjacent 15-story buildings increase in responses of drift and shear force, 20 and 16 percent, respectively. In tall buildings (15-story in this study) with the same height adjacent structures, the acceleration up to 15% and drift up to 23% decrease with two 10-story adjacent structures and shear force increases up to 35% with two 5-story adjacent structures. On the other hand accepting the results of common structural dynamic analysis lead to unsafely design for tall buildings, and for short structures are not affordable.