ABSTRACT
The influence of spatial variations of mass eccentricities on the earthquake induced torsion in buildings is investigated using both analytical and numerical modeling results. The objective of this research was to provide practical design guidelines for minimizing the torsional response of building structures. An analytical solution is proposed, which identifies the optimum location of a key structural element for which the torsional response of a structure is minimized for any practical spatial variation of mass eccentricities. The analytical solution requires firstly the quantification of the structural element frequencies which are determined from the corresponding individual bents when they are assumed to carry, as planar frames, the mass of the complete structure and, secondly, the fundamental frequency of the uncoupled structure with fictitious floor masses. Both of which can be easily determined by any commercial structural software. The numerical modeling results show that for any spatial variation of mass eccentricities the top rotations and base torques have an inverted peak, which indicates an optimum location of the key structural element, for which the torsional response of the structure is minimized. The results demonstrate that by reversing the spatial distribution of mass eccentricities, the required optimum location of the key element is shifted to a symmetrical position with respect to its nominal location when no mass eccentricities are taken into account. The accuracy of the analytical solution is verified with reasonable accuracy by the numerical modeling results on 9 storey buildings with in plan and in elevation irregularities and spatially varying mass eccentricities.
