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Earthquakes and Structures
  Volume 9, Number 1, July 2015, pages 145-171

Ratio of Torsion (ROT): An index for assessing the global induced torsion in plan irregular buildings
Chrysanthi G. Stathi, Nikolaos P. Bakas, Nikos D. Lagaros and Manolis Papadrakakis

    Due to earthquakes, many structures suffered extensive damages that were attributed to the torsional effect caused by mass, stiffness or strength eccentricity. Due to this type of asymmetry torsional moments are generated that are imposed by means of additional shear forces developed at the vertical resisting structural elements of the buildings. Although the torsional effect on the response of reinforced concrete buildings was the subject of extensive research over the last decades, a quantitative index measuring the amplification of the shear forces developed at the vertical resisting elements due to lateraltorsional coupling valid for both elastic and elastoplastic response states is still missing. In this study a reliable index capable of assessing the torsional effect is proposed. The performance of the proposed index is evaluated and its correlation with structural response quantities like displacements, interstorey drift, base torque, shear forces and upper diaphragm’s rotation is presented. Torsionally stiff, mass eccentric singlestory and multistory structures, subjected to bidirectional excitation, are considered and nonlinear dynamic analyses are performed using natural records selected for three hazard levels. It was found that the proposed index provides reliable prediction of the magnitude of torsional effect for all test examples considered.
Key Words
    torsional effect; mass eccentric; torsionally stiff; center of rigidity; nonlinear dynamic analyses
Chrysanthi G. Stathi, Nikolaos P. Bakas, Nikos D. Lagaros and Manolis Papadrakakis: Institute of Structural Analysis & Antiseismic Research Department of Structural Engineering, School of Civil Engineering, National Technical University, Athens 9, Iroon Polytechniou Str., Zografou Campus GR-157 80, Athens, Greece

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