Seismic Behaviour of Typical Mass Eccentric Buildings

Abstract

Buildings, which are symmetric in mass and stiffness also display torsional coupling due to the asymmetric distribution of mass over the floor slabs, are called mass eccentric systems. When the otherwise translation only modes are coupled with torsional effects, it can result in unpredictable deformations and the failure of the entire structure during a seismic event. Mass eccentricity mainly occurs due to the presence of concentrated mass elements such as water tanks, machineries etc. in certain floor levels. Failures of mass eccentric buildings reported in past earthquakes indicate the inadequacy of the existing codal procedures. As a first step of investigation, the present study focusses on the behavior of typical mass eccentric buildings with regard to free vibration and time history responses. It is observed that natural period of the structure steadily increases with eccentricity of the mass. Also the shear forces in the columns adjacent to the center of mass are found to undergo increasing trend but those located far away undergo a decreasing trend. When eccentricity is provided in opposite directions in adjacent storeys of a two storey building, the shear forces are found to be reduced.