Quantitative assessment of seismic design provisions for buildings with torsional irregularities

ASCE/SEI 7 design requirements for seismic-induced torsion in buildings are evaluated to determine their effectiveness for resisting seismic-induced collapse of torsionally irregular buildings. The ASCE/SEI 7-16 provisions are found to be generally conservative for most torsionally irregular building configurations—exceptions are some buildings that rely heavily on lines of lateral resistance orthogonal to the design earthquake force to resist torsional moments, and also some torsionally flexible buildings designed using modal response spectrum analysis. Modifications to provide better consistency in collapse resistance over a large range of building configurations and degrees of torsional irregularity are recommended. The study also demonstrates that buildings classified as extremely torsionally irregular may not need to be prohibited from Seismic Design Categories E and F, as long as the lateral system is proportioned properly.