Assessment of design recommendations for torsionally unbalanced multistory buildings

Multistory models are studied to assess design recommendations for torsionally unbalanced multistory buildings. Structural systems are assumed as shear beams with nonlinear lateral-resisting elements oriented along two orthogonal directions and subjected to a bidirectional earthquake ground motion. Five-story rigid-diaphragm models with mass or stiffness eccentricity are considered in the study. Accidental eccentricity is not included in the modeling and, therefore, its related recommendations are not assessed. Design recommendations studied here are based on the simple static procedure and include two values and an expression for the amplification factor a to compute story eccentricities, three values of the torsion-shear reduction factor delta, an additional lateral force F-t to be applied at the building top level, and a minimal story eccentricity for the building. Design recommendations to control ductility demands of torsionally unbalanced multistory buildings are given.