Pushover analysis of symmetric and asymmetric reinforced concrete buildings

Abstract

It has been observed that conventional elastic design methods don’t give realistic basis to control seismic performance of structures in severe earthquakes. Inelastic time-history methods are very powerful but computationally, being very expensiveand complex, are not feasible for most of the practical applications. The pushover method of analysis, being a nonlinear static method, considers inelastic response characteristics and it can be used to estimate the dynamic demands imposed on the structures during seismic excitation. In reinforced concrete buildings, irregularities are introduced to meet various functional requirements and architectural demands. These irregularities add an additional effect of torsion or sudden change in stiffness which affects the demands of the structure. In the present paper, 3 storey and 6 storey symmetric buildings have been analyzed using pushover analysis. The plan of the same buildings is modified and plan asymmetry is created by introducing eccentricities of magnitudes varying from 5 to 20 % about both the principal axes. Various vertical irregularities of soft storey and extreme soft storey are also introduced by increasing the height of the ground storey. All the above models have been analyzed using pushover method. The capacity curve and performance point are obtained for all the models. Based on analytical results, comparisons between symmetric, plan asymmetric and vertically asymmetric buildings have been drawn. SAP 2000 has been used to carry out the pushover analysis. It has been observed that beyond elastic range, developed base shear increases with increase in plan asymmetry and decreases with increase in vertical asymmetry. Same trend is followed for ultimate base shear. Also, the performance point lies in elastic range and it is relatively on left side for 3 storey buildings when compared with 6 storey buildings, indicating 3 storey building to be safer.