Nonlinear Response Analysis of Plan and Vertical Asymmetric Reinforced Concrete Buildings under Directional Seismic Loadings

Abstract

A Nonlinear dynamic analysis of plan and vertical asymmetric RCC structure is performed when the buildings are subjected to seismic forces. The time history analysis is employed to investigate the behavior of the buildings. A MATLAB program is developed to using Newmark’s beta method and Newton-Raphson iteration technique. Three different earthquakes, i.e., Irpinia, 1980; Loma Prieta, 1989 and Chi-Chi, 1999 with magnitudes 6.2, 6.9 and 7.7 respectively are considered. The earthquake angles of 0°, 30°, and 45° are studied. The plan-asymmetry in the building is introduced by imposing uni-axial eccentricities of 6m, 12m, and 18m by shifting the location of the core. The vertical mass and stiffness asymmetry at different building levels is introduced by varying the mass or stiffness in the vertical direction. The peak displacement and the inter-storey drift ratio (ISDR) are evaluated. From the study it is observed that the plan asymmetric structural response has been increased with the increase in eccentricity from 6m to 12m. The eccentricity beyond 12m has not showed any increase in the structural response due to coupling effect. In comparison to stiffness and mass vertical asymmetric buildings, stiffness asymmetry at bottom floor and mass asymmetry at top floor have shown larger response and ISDR in all the earthquakes and angles of study. All the peak responses in plan and vertical symmetric structures are observed at the earthquake angle of 0^o. The peak displacements are in the order of 35m in X direction and 80m in the Y direction for the plan asymmetric structures. The vertical stiffness asymmetric structures showed peak response of 140mm and 300mm in the X and Y directions, which showed the displacement beyond the elastic limit. The building with mass asymmetry at top showed about 400mm in the X direction and 550mm in the Y direction. This behaviour clearly shows the material failure. Hence a detailed analysis is recommended in the analysis and design of the asymmetric structures especially to predict the material failure.