Considération de la torsion pour l'analyse sismique non-linéaire de noyaux en béton armé

Reinforced concrete (RC) cores are used in many residential multi-story buildings as the primary seismic force resisting system (SFRS). Due to architectural limitations, these buildings are often torsionally lexible. To assess the effect of torsion on the nonlinear seismic response of RC cores, a wide-column model with modules (WCMM) using fiber elements is proposed. The nonlinear warping and the nonlinear biaxial (P-Mx-Mx) cyclic behaviors of the WCMM are validated against experimental results and exhibit excellent agreement. According to modal and linear time history analyses, the proposed model can adequately capture the dynamic characteristics and seismic response of core structures, including torsion. The proposed WCMM is then extended to the nonlinear range to perform three-dimensional (3D) time history analyses of a typical RC building structure located in Eastern North America (ENA) that is subjected to high-frequency ground motions (approximately 10 Hz). Three different building configurations with increasing torsional flexibility (B=1.7, B=2.1 and B=2.5, according to the current National Building Code of Canada) are studied to investigate the effect of torsion on the seismic behavior. The nonlinear envelopes of key response parameters are similar to the design envelopes obtained from the linear response spectrum analysis of a shell elements model (B=1.7) with proper inelastic force modification factors. Aside from the story torque, the shear and moment demands remain relatively constant, regardless of the B value. The effective shear stiffness must be carefully selected in the WCMM to avoid large questionable rotations. A correlated delay can be observed between the translational and rotational peak displacements in the nonlinear time histories of the buildings analyzed.