Modified Modal Response Spectrum Analysis of Plan Irregular Highly Torsionally-Stiff Structures Under Seismic Demands

Abstract

Modal response spectrum analysis is the common procedure used to estimate the maximum seismic response of structures for assessment and design. However, previous studies show that this procedure provides unconservative results for highly torsional stiff systems such as shear wall buildings that show inelastic behaviour under seismic demands associated with the ultimate limit state. This paper presents an artifice that allows to obtain improved estimations of design demands for torsionally stiff buildings with rectangular plan via modal spectral analysis of a modified elastic model. In this model, the centre of mass is displaced by a quantity termed additional mass eccentricity, which is a function of the plan aspect ratio, the actual eccentricity and the design behaviour factor. Equations to calculate additional mass eccentricity for seismic design applications are given.