Inelastic Link Element for EBF Seismic Analysis

A formulation for modeling links in eccentrically braced steel frames (EBFs) subjected to random inelastic cyclic loading is presented. The formulation is plasticity-based, and includes shear and flexural yielding. In addition, combined isotropic and kinematic shear strain-hardening effects are accounted for, as well as flexural strain hardening. The formulation is shown to accurately predict the behavior of test specimens involving short links. Inelastic seismic analysis of EBFs with short links was conducted to illustrate the effect of link-modeling assumptions on EBF response. The analysis results show that link strain hardening can have a pronounced effect on EBF response, leading to larger member forces in braces and columns attached to the links. Furthermore, combined flexural and shear yielding occurred in the links adjacent to columns, indicating the need to include these types of inelastic deformations in the link-modeling formulation. Finally, the use in the analysis of viscous damping in the link was found to cause excessive axial forces to develop in braces and columns adjacent to yielded links. To reduce this effect, a form of nonproportional viscous damping is illustrated.