Accidental Torsion and Amplification of Accidental Torsion

This chapter examines issues related to torsional loading: torsional irregularities, accidental torsion, torsional amplification, and application of accidental torsion to structures analyzed using the equivalent lateral force or modal response spectrum (MRS) approaches. Systems with rigid and semirigid diaphragms are considered. Accidental torsion need not be considered for systems with flexible diaphragms. A three-dimensional analysis is needed to determine if a torsional irregularity exists and whether the accidental torsion must be magnified. To determine if a torsional irregularity exists, interstory drifts (not displacements) are monitored at the extreme edges of the building under a loading that consists of the design lateral forces and (plus or minus) accidental torsion. The chapter discusses the application of accidental torsion in systems with somewhat flexible semirigid diaphragms. It concludes with a discussion of the application of accidental torsion and torsional amplification in MRS analysis.