Coupled Lateral Torsional Response of Buildings to Ground Shaking: Fid-Bau Portal

Coupled Lateral Torsional Response of Buildings to Ground Shaking

C. L. Kan / A. K. Chopra

This study of earthquake response of buildings for which the lateral motions are coupled with the torsional motion is presented in three parts: (1) The elastic response of torsionally coupled one-story buildings to earthquake ground motion, characterized by idealized shapes for the response spectrum, is studied. Influence of the basic system parameters on the response is investigated. The relationship between the forces -- base shears and torque -- in a torsionally coupled system and the base shear in a corresponding torsionally coupled system and the base shear in a corresponding torsionally uncoupled system is established, and the effects of torsional coupling on earthquake forces are identified; (2) A simple procedure is developed for the analysis of the elastic response of a particular class of torsionally coupled multistory buildings to earthquake ground motion, characterized by smooth response spectra; (3) With the aid of perturbation analysis of vibration frequencies and mode shapes it is shown that any lower vibration mode of a torsionally coupled building may be approximated as a linear combination of three vibration modes of the corresponding torsionally uncoupled system (a system with coincident centers of mass and resistance but all other properties are identical to the actual system): one translational mode along each of the two principal axes of resistance and one mode in torsional vibration. This result provides the motivation for a simpler -- relative to the standard -- procedure for analyzing the response of torsionally coupled multistory buildings to earthquake ground motion.