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Earthquakes and Structures
  Volume 26, Number 5, May 2024 , pages 349-361

Using an appropriate rotation-based criterion to account for torsional irregularity in reinforced concrete buildings
Akshara S P, M Abdul Akbar, T M Madhavan Pillai, Rakesh Pasunuti and Renil Sabhadiya

    Excessive torsional behaviour is one of the major reasons for failure of buildings, as inferred from past earthquakes. Numerous seismic codes across the world specify a displacement-based or drift-based criterion for classifying buildings as torsionally irregular. In recent years, quite a few researchers have pointed out some of the inherent deficiencies associated with the current codal guidelines on torsional irregularity. This short communication paper aims to envisage the need for a revision of the displacement-based guidelines on torsional irregularity, and further highlight the appropriateness of a rotation-based criterion. A set of 6 reinforced concrete building models with asymmetric shear walls are analysed using ETABS v18.0.2, by varying the number of stories from 1 to 9, and the torsional irregularity coefficient of various stories is calculated using the displacement-based formula. Since rotation about the vertical axis is a direct indication of the twist experienced by a building, the calculated torsional irregularity coefficients of all stories are compared with the corresponding floor rotations. The conflicting results obtained for the torsional irregularity coefficients are projected through five categories, namely mismatch with floor rotations, inconsistency in trend, lack of clarity in incorporation of negative values, sensitivity to low values of displacement and error conceived in the mathematical formulation. The findings indicate that the irregularity coefficient does not accurately represent the torsional behaviour of buildings in a realistic sense. The Indian seismic code-based values of 1.2 and 1.4, which are used to characterize buildings as torsionally irregular are observed to be highly sensitive to the numerical values of displacements, rather than the actual degree of rotation. The study thus emphasizes the revision of current guidelines based on a more relevant rotation-based or eccentricity-based approach.
Key Words
    displacement-based criteria; floor rotations; plan irregularity; structural irregularity; torsional irregularity
Akshara S P, M Abdul Akbar and T M Madhavan Pillai: Department of Civil Engineering, National Institute of Technology Calicut, Kozhikode-673601, India
Rakesh Pasunuti: L&T Construction, Mount Poonamallee road, Manapakkam, P.B. No. 979, Chennai, India
Renil Sabhadiya: KEC International, RPG centre, 30, Forjet street, near Bhatia hospital, Tardeo, Mumbai, India

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