Effect of Brace Locations and Accidental Eccentricity on the Response of Asymmetric Structures

The first objective of this paper is to consider asymmetric location of braces in steel structures. For this purpose, eccentricity effect of the center of stiffness toward the center of mass and the torsion caused by that is considered. For that, a building, which has been constructed in the past, is investigated by changing the arrangement of braces and the amount of steel consumption, as an important economic indicator, is considered in each items. Then the displacement parameter, which is the suitable criterion for detection of structural damages, was evaluated. Finally, changes of base shear toward eccentricity are examined. It is shown that with closing the center of mass and stiffness and reducing the eccentricity using the appropriate location of braces, how much base shear and structure weight (steel consumption) is reduced. Then, the sensitivity of the asymmetric structure under torsion to analysis type is investigated. For this purpose, two types of analysis included pseudo-static and dynamic spectral analysis are studied. As well, in the second objective, the effect of considering the accidental eccentricity is evaluated in designing phase of buildings. For this purpose, two asymmetric structures in plan are designed with and without considering the accidental eccentricity (ea) equal to ۵%. Whereas according to Iranian Seismic Code No. ۲۸۰۰, considering ea is not necessary for the structures. These structures are analyzed by nonlinear time history and results indicate that ea can reduce the response of structure considerably.

Keywords:

Asymmetric structures , Brace locations , Accidental eccentricity , Nonlinear dynamic analysis , Pseudo-static analysis , Dynamic spectral analysis