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Structural Engineering and Mechanics
  Volume 74, Number 5, June10 2020, pages 699-709

Determination of torsional irregularity in response spectrum analysis of building structures
Fatemeh Aliakbari, Sadegh Garivani and Ali Shahmari

    Torsional irregularity is one of the most probable types of horizontal irregularity and existence of this irregularity in most of the structural loading codes is determined by calculating the ratio of the maximum to the average story drift. No specific method has been previously recommended by the codes to calculate the mentioned ratio in the response spectrum analyses. In the current investigation, nine steel building structures with different plan layouts and number of stories have been analyzed and designed in order to evaluate the efficiency of three methods for calculating the ratio of the maximum to the average story drift in the response spectrum analyses. It should be noted that one of these methods is the approach used by current version of ETABS software andother ones are proposed in this paper. The obtained results using the proposed methods are compared with the time history analysis results. The comparisons show that one of these methods underestimates the mentioned ratio in all studied models, however, the other two methods have shown similar results. It is also found that the plan layouts and irregularities can affect how these methods estimate the ratios compared to those obtained by the time history analysis. Generally, it can be concluded that all of these methods can properly predict the ratio with acceptable errors.
Key Words
    response spectrum analysis; Irregular structures; Horizontal irregularity; Torsional irregularity; Extreme torsional irregularity
Fatemeh Aliakbari, Sadegh Garivani: Faculty of Engineering, University of Bojnord, Bojnord 94531-55111, Iran
Ali Shahmari: Faculty of Civil and Environmental Engineering, Tarbiat Modares University, Tehran 14115-143, Iran

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