Critical review of codal provisions on the torsional irregularity

Abstract

Buildings with irregularities have consistently been highly vulnerable to seismic events. The earthquake events have been showing the failure patterns of the reinforced concrete buildings with various irregularities. But the large number of buildings have been existing and being constructed with irregularities both in the urban as well as rural areas of developing countries. Various irregularities have been defined in international standards. But still, there is a need to study the combined irregularities of the building. In this study, the various country codal provisions on torsional irregularities in the reinforced concrete buildings have been reviewed and compared. Most of the codes have considered the edge displacements as the measure of torsional irregularity criteria. The amplification factorshave been used for structural eccentricity and accidental eccentricity to increase the design forces. The torsional flexibility based on the ratio of the natural period of torsional mode
and translational mode, stiffness eccentricity ratio, and the mass factor based on the radius of gyration of mass about the center of mass of the building have been introduced in the draft code IS 1893-2023, Part-2. The limiting value have been prescribed by the code for torsional flexibility factor to prevent the failure of buildings due to torsional flexibility. In this paper, various significant factors affecting the seismic performance of the buildings due to torsional irregularity have been reviewed.