Investigation on torsional amplification factor for irregular structures in plan

Hassan Bagheri¹ Seyed Mobin Hashemi² Kourosh Mirziea³

1) Port and Maritime Organazation Email:
2) Islamic Azad Univercity, Boushehr Branch
3) Islamic Azad Univercity, Boushehr Branch Email:

IOI Code : XEFB-HCFFA
Publication : 2nd International Congress on Civil Engineering, Architecture, Building Materials and Environment(caucong.com/2nd)
Abstract :
    According to the provisions of standard2800, when the maximum relative displacement at the end of structure, computed including accidental torsion with Ax=1, is more than 1.2 times the average of relative displacement at the two end of the structure, the structure is irregular in plan and has a low torsional stiffness. The past research and experiences indicate that the structures with low torsional stiffness don’t have an acceptable performance in earthquake. To decrease the influence of low torsional stiffness, Standard2800 suggest multiplying torsional amplification factor (Aj) to the accidental torsion. In this paper the torsional amplification factor (Aj) evaluated parametrically. The results of this study shows when structures are torsional flexible, the suggested formula for torsional amplification factor(Aj) does not give acceptable numbers.

Keywords : torsional flexible structures frequency ratio flexible & stiff edge torsional amplification factor eccentricity