Finite element study of knee element on the behavior of moment resisting frame in steel shear wall

Steel shear walls are an innovative system that resist to lateral loads such as wind and earthquakes. In this paper, the effect of knee element on the behavior of moment resisting frame with steel shear wall has been numerically investigated by changing parameters such as the number and types of link beam (bending, bending-shear and shear behavior), shear wall thickness and span length-to-height ratio. The results showed, the most effective one that affect the bending behavior of the frame is the case with 4 link beams with shear behavior dominated. Also, by changing the length of the link beam from bending to bending-shear and then shear behavior, the values of stiffness, bending strength and dissipated energy have increased. Failure mode in this system depends on how the shear plate is connected to the boundary members. In the absence of knee element, stress is notably concentrated at the interface of beam to the column connection, Conversely, with the inclusion of 4 link elements, the damage and stress concentration are dispersed away from the links and widely distributed in the filler plate thus the maximum plastic capacity of steel shear plate is used. The results demonstrate that incorporating four shear-dominated link beams provides the most balanced improvement, enhancing the lateral stiffness, ultimate strength, and cumulative energy dissipation by up to 143%, 102%, and 112%, respectively, compared to an unreinforced wall. The performance of moment-resisting frames without link beams is characterized by a less effective distribution of stress and inelastic strain compared to other samples and in contrast, the presence of link beams has been associated with a re-hardening effect in the force-displacement response of steel shear walls, resulting in improved bending performance.