Elastic stiffness and bearing mechanism of eccentrically braced steel frames

Eccentrically braced steel frames have great ductility and energy dissipation, but their elastic stiffness is influenced by the length of the braces. The stiffness of these frames is important for computing story drifts and link rotations, which have prescribed limits. The yield and ultimate bearing capacity of eccentrically braced steel frames can be predicted by analyzing their individual components. This paper proposes a method to calculate the elastic stiffness and bearing capacity of K-type, D-type, and V-type eccentrically braced steel frames. To calculate the elastic stiffness of these frames, the displacement of a story can be obtained by summing the deformations of the individual components. The link shear and brace axial force of a story are also considered using structural mechanics. This allows for estimating the elastic stiffness of eccentrically braced steel frames in the early design phase. Based on the virtual work principle and the ideal failure mode of these frames, the yield and ultimate bearing capacity of eccentrically braced steel frames are proposed using frame drift angle and verified by experimental results. The theoretical stiffness of these frames is compared with finite element models. The finite element analysis and experimental results show that the elastic stiffness, yield bearing, and ultimate bearing are very close with only about 10% error, verifying the high accuracy of the formula suggested in this paper.