NUMERICAL STUDY OF AXIAL LOAD EFFECT ON THE SEISMIC BEHAVIOR OF SHEAR LINKS IN ECCENTRICALLY BRACED FRAMES

Abstract

High ductility and stiffness of the eccentrically braced frames (EBFs) are provided by the isolated beam segments between two braces or between brace and column which is referred as links. The remarkable hysteresis behavior of shear links in EBFs is so appealing to seismic design that they have also been used in other types of structure applications such as fuse members that provides required ductility and energy dissipation. Therefore, using shear links is becoming more and more popular not only in buildings but also in bridges.

In order to assure that shear links provide required strength and ductility of the structure, studying the effect of key parameters on hysteretic behavior of shear links is of interest. High axial load is one of the key parameters which affect hysteretic behavior of shear links because premature flange local buckling might occur and results in deterioration in shear capacity, ductility, and energy dissipation of the links.

The effect of high axial load ratio on shear capacity and ductility of shear links is studied by numerical simulation in this research. Finite element (FE) model was calibrated using experimental data for two link beams, including one link subjected to high axial load ratio. Nonlinear FE analysis of twenty-two shear link specimens was carried out to determine the plastic shear capacity of shear links with different link length and axial load level. In comparison with the formula given in 2010 AISC Seismic Provisions, a reduction factor is proposed to modify the code-specified design equation. Furthermore, local buckling due to high axial load was observed in link specimens, which precludes the shear links from providing the code-specified rotation capacity. The detrimental effect of high axial load ratio on ductility of the shear links was also observed from cyclic loading analysis of six link specimens in this research.