Behavior of shear wall with base opening

Abstract

Shear wall, commonly used to provide lateral stiffness of buildings, and is an important element for seismic resistance of a stmcture. Shear walls are frequently pierced for doors, windows al)d corridor openings. Also provision of parking at basement or ground level may require opening to be kept at the base of a shear wall. As the entire lateral load acting in a shear wall is transmitted to the ground through the base, it is the most critical section of a shear wall. So openings at that level will affect its overall stiffness as compared to shear wall without opening. [n this research work, concentration is given to establish the range of base opening that may be allowed without significantly affecting the strength and stiffness of a structural wall. The behavior of both planar and box type shear wall (core wall) with varying percentages of base opening have been studied. With the above objective, finite element package ANSYS (2000) has been used for modeling the shear wall and study its behavior in tenns of stress pattem and stiffness variation due to incorporation of opening at base. The behavior of shear wall for different opening width have been studied and compared to that of a shear wall without opening. Three parametric ratios such as deflection ratio, maximum shear stress ratio and maximum flexural stress ratio have been studied. The ratios are calculated as the ratio of corresponding values of a shear wall with and without base opening. A set of non-dimensional graphs have been prepared featuring. important parameters which will guide the designer to choose appropriate opening width without hampering the lateral stiffness significantly. An investigation is also perfonned to show how the degradation of stiffness of shear wall with base opening can be compensated using additional portion of the shear wall. It is observed that these three parametric ratios increase with the increase of percentage of base opening. However, the rate of increase of these ratios has been found to be relatively low up to 60% base opening. Beyond 60% opening, these ratios increase rapidly, meaning strength and stiffness degradations are excessive beyond this limit. It is also observed that, with the introduction of compensating elements, it is feasible to fully compensate the deflection and flexural stress ratios and also bring about significant improvement in the shear stress ratio. Based on the findings of the study, it has been recommended that in high-rise construction a provision of base opening up to 50% of the length of the wall may be considered as a feasible option.