IOSR Journal of Engineering (IOSRJEN) www.iosrjen.org ISSN (e): 2250-3021, ISSN (p): 2278-8719 Vol. 04, Issue 01 (January. 2014), ||V6|| PP 18-27 International organization of Scientific Research 18 | P a g e Optimization of Viscous Dampers with the Influence of Soil Structure Interaction on Response of Two Adjacent 3-D Buildings under seismic load Ahmed Abdelraheem Farghaly (Faculty of Industrial Education, Sohag University, Egypt) Abstract: - 3D two adjacent buildings with different heights founded in different kinds of soil connected with viscous dampers, with especial arrangement in plane, were investigated. The soil for three different kinds of soil (stiff, medium and soft) were model as 3D Winkler model to give the realistic behavior of adjacent building connected with viscous dampers. The investigation is carried out to study the structural responses of two adjacent buildings connected with viscous dampers under various earthquake excitations taking in the account the effect of different kinds of soil beneath the buildings. The introduction of soil-structure interaction requires a mathematical model for the foundation and surrounding soil, use SAP2000n to model the system. A range of soil properties and soil damping characteristics are chosen which gives broad picture of connected structure system behavior on influence of soil-structure interaction. Its conclusion that the response of connected structures system founded on soft soil are more critical than those founded on stiff soil. The behavior of connected structures is different from those with fixed base bigger by nearly 20%, and the efficiency of viscous dampers connecting the two adjacent buildings is reduced by nearly 25% less than those founded on stiff soil. Key words: - 3D analysis – Adjacent buildings – Viscous damper – Couple buildings – SSI – Connecting adjacent building with viscous damper – optimum number of dampers. I. INTRODUCTION Many researchers have concerned with the performance of connected adjacent buildings subjected to earthquake, it studied using different kinds of dampers and compared its efficiency. Most of researches models exercise 2D two connected adjacent buildings with fixed base; so that the reality of its results is doubtful, to overcome these problems the 3D models with taking in consideration soil structure interaction must be analyzed, to get the closest to reality performance of connected two adjacent building with dampers system. In this study a real 3D two adjacent buildings connected with viscous dampers taking in consideration the soil structure interaction and its effect on the performance of the system subjected to earthquake. The damages observed from seismic pounding, i.e., heavy and repeated collision of buildings, are devastating and particularly frequent in dense urban centers [13]. Several studies have investigated the use of damper connectors in order to reduce pounding induced damage and to increase the seismic resistance of a structure [2]. Hwang et al. (2007) [6] employed viscous dampers at the connection between the exterior and interior structures to enhance earthquake resistant performance of the factory structures. Viscous damping involves taking advantage of the high flow resistance of viscous fluids. When the damper is installed in a building, the friction converts some of the earthquake energy going into the moving building into heat energy. The force depends on the size and shape of the orifices and the viscosity of oil. Strong temperature dependence is observed. The forces developed in a viscous damper are proportional to the velocity of its deformation. Fluid viscous dampers put out virtually zero force at the low velocities associated with thermal motion. Fluid inertial dampers have several inherent and significant advantages: linear viscous behaviour, insensitivity to stroke and output force; easy installation; almost free maintenance; reliability and longevity. Fluid viscous dampers allow the structure to re-centre itself perfectly at all times. Kasai (1992) inserts a viscoelastic or viscous dampers in the closely spaced adjacent buildings thereby increasing their damping properties substantially. The dampers placed inside the adjacent buildings have the potential to reduce significantly the effect of pounding due to the following reasons: • They reduce the maximum displacement of the buildings; • They promote the in-phase motion of both buildings; • Should the pounding occur the impact is absorbed by the dampers in the vicinity of pounding level, thereby preventing propagation of its effect to other storey levels.