Response Spectrum Analysis of Response of Building with Setbacks

Abstract

The past earthquakes have shown catastrophic effect on the buildings with irregularities. It was seen that the buildings with irregularities are more prone to earthquake then the regular building. The structure with irregularities are called irregular structures. Irregularities in a building can be due to the uneven distribution of mass, stiffness and geometry of the structure. In the present paper a special case of vertical irregularity i.e. setback is discussed. Seven types of buildings are taken for analysis, out of which one is regular building and rest are buildings with setbacks at different storey height. All six irregular structures are compared with the regular structure on the basis of shear force, axial force and bending moment at setbacks. It was found that the value of axial force in all beams and columns are increasing drastically as we move from regular to irregular structure. It was interesting to note that, however the mass of the building is reducing but forces at setbacks are increasing to a great extent. The analysis suggest that the setbacks introduced in a building can be proven disastrous at the time of earthquake hence it is not recommended to introduce setbacks in a building.