Torsional Amplification of Peak Floor Accelerations in Torsionally Irregular RC Buildings with Different Lateral Systems

This study investigates torsional amplification of peak floor accelerations in low- to mid-rise reinforced concrete buildings. Linear time-history analyses are conducted using 24 ground motions matched to the Montreal uniform hazard spectrum for site class C, considering torsionally irregular moment-resisting frames and shear wall systems. Results indicate that the torsion-based amplification factor increases linearly up to mid-height and remains nearly constant toward roof. Maximum flexible-side amplification correlates linearly with torsional irregularity index and is independent of structural system and building height. A height-dependent formulation is proposed for integration into the NBCC 2025 height amplification factor and validated against numerical simulation.