Static and Dynamic Analysis of Coupled Shear Wall in Highrise Structure

Abstract

Taipei 101, Petronas twin Towers, Sears Tower and World Trade Centre are just a few examples testifying to the human aspiration to build increasingly highrise structures. The basic structural behavior of highrise structure is similar to the cantilever coming out of the ground. The lateral forces generated from wind and earthquake is critical in highrise structures. Therefore to resists these lateral forces, lateral load resisting structural systems are required. The examples of lateral load resisting structural systems are rigid frame, braced frame, shear wall and coupled shear wall.

From the past seismic events like, it observed that structural wall subjected to brittle kind of failure due to insufficient ductility to control its behavior. Then the researchers came up with new idea by connecting the walls through the framing beams, which is known as coupled shear wall. In CSW, the forces are redistributed through out the entire structure instead of concentrating at base of walls, which is happened in case of structural wall. The performance index of the coupling action is the degree of coupling. The degree of coupling (DC) depends on the geometry of CSW. The geometry of CSW includes wall length, wall height (or number of storey) depth and span of coupling beam. Therefore a parametric study is carried out to study the behavior of CSW. The behavior of CSW includes elastic static, elastic dynamic and inelastic static behavior.

From the elastic static behavior of CSW, it is observed that as the depth of coupling beam increases the degree of coupling increases at the lower storey and DC increases for the lower depth of coupling beam at higher storey. The time period of CSW is studied and compared with current codal provision of IS 1893 : 2002, Wallace and Moehle’s formula and O. Chaallal’s formula. From the analysis results of ETABS, it is observed that the time period is closer to the Wallace and Moehle’s formula and there is considerable difference between codal provision and analysis results. In the present scenario, the codal provision needs to incorporate the dimensions of CSW elements in the time period formula for CSW building. As far as inelastic behavior is concern, the failure pattern of CSW is studied considering different parameters. The guideline for well proportioned CSW is proposed in terms of span to depth ratio of coupling beam. When the degree of coupling beam increases the formation of plastic hinges also increases. More the coupling action more will be the dissipation of energy. Therefore response reduction factor in case of CSW building can be increased in compared to structural wall building.

The seismic design of CSW and its foundation for different parameters is carried out. The effect of soil condition on the responses of CSW and its foundation are also studied. As the allowable bearing capacity of soil decreases the axial force decreases and moment increases in the wall rapidly at lower storey. For the implementation of CSW concept, the response of CSW in a 51-storey building is studied. At present, the construction of 51-storey building is going on in Mumbai.