Estimation of Fundamental Natural Period of RC Frame Buildings with Structural Walls

Abstract

The natural vibration characteristics of a structure play a significant role in estimation of seismic behaviour of a structure. The principal natural vibration characteristic, namely the natural period of vibration, is experimentally estimated by either carrying out ambient vibration studies or from the observed seismic behaviour of the building. The design guidelines of different countries also provide some estimate of the natural period by prescribing empirical expressions. Reinforced Concrete (RC) frame buildings with structural walls are commonly prescribed for highrise buildings in regions of strong earthquake shaking. Currently, the Indian Earthquake Code IS:1893 (Part 1): 2002 does not prescribe any expression for estimation of natural period of an RC frame building with structural wall. The present study is intended to prescribe such an expression based on parametric studies of structural walls in RC frame buildings. In the current study, a symmetrical plan RC frame building is modeled in the computer program SAP2000. The beams and columns have been modeled as frame elements and the slabs and shear walls have been modeled as shell elements. The building is assumed to be founded on rocky stratum with the restraint of all translational and rotational degrees of freedom of the nodes at the bottom of the columns. The investigations were carried out varying three parameters of the structural wall, namely (a) height, (b) modulus of elasticity of concrete, and (c) thickness. Modal analysis was carried out for each building model for obtaining the fundamental natural period of vibration. Based on the regression analysis of the results of parametric studies, an expression is proposed for obtaining the fundamental period of vibration of RC frame buildings with structural walls.