Investigation of the Rocking Motion of RC Buildings Dual Shear Wall-Frame Structures

The foundation is usually assumed to be rigid, in the design of buildings and the impact of soil type on the flexibility of the foundation is not directly applied in simulations. However, considering the interaction between soil and structure can affect the structure's response. On the other hand, shear walls are widely used in concrete buildings today. When these walls are affected by severe earthquakes, elevation and oscillating movements can be seen at the base of these systems. As a result, the foundations of these systems are lifted from the ground under certain conditions. In this study, the support conditions of columns and shear walls in concrete RC buildings with dual shear wall-frame were investigated. For this purpose, at first, an 8-storey concrete building with a dual RC shear wall-frame system was analyzed and designed in accordance with the national building regulations of Iran using SAP2000 software. In the next step, the outer frame of the structure was simulated using finite element method and ABAQUS software under two different boundary conditions. In the first case, the effect of the foundation was evaluated as rigid and in the second case, the effect of the foundation was evaluated with the possibility of lifting (creating a rocking motion). In order to consider the possibility of lifting the foundation and local-nonlinearity of the soil (creating a rocking motion) springs depending on the type of soil were defined with Bowles stiffness values. The variables include the type of boundary conditions, the strength of the concrete (C21, C40, and C60) and the type of soil (Clay, loose sand and dense sand). The results showed that considering the possibility of lifting the structure by a rocking motion depends on the characteristics of the soil under the foundation, so that the type of soil can play a role in stress, lateral displacement and base shear of the structure. Also, in frames where the boundary conditions of the column and shear walls were considered to be flexible, the change in soil type caused the maximum stress changes of the frame to reach about 60%.