Proposed Stiffener Spacing Requirements for Intermediate Length Links in Eccentrically Braced Frames

This paper assesses the stiffener spacing design requirements according to AISC-341-22 for intermediate length links in eccentrically braced frames (EBFs) through nonlinear continuum finite element simulations of 40 different intermediate length links. In approximately half of those, the current AISC-341 requirements do not ensure satisfactory performance prior to the targeted inelastic design rotation angle depending on the nondimensional link length. This is attributed to the inelastic deformations that tend to concentrate in the end panels, thereby leading to rapid strength deterioration of the link. Consequently, we propose an alternative stiffener spacing design requirement for intermediate EBF links. The new rule relies on the numerical solution of the inelastic plate buckling of a steel plate under shear thrusts coupled with normal stresses due to flexure, which is indicative of the stress state in webs of intermediate EBF link webs. The proposed rule is approximated by an empirical expression to retain simplicity as part of the design process. The proposed rule is then verified through complementary continuum finite element simulations of intermediate link geometries. Intermediate links featuring moderately ductile flange plates meet the established inelastic design rotation angle requirements according to AISC-341-22, conditioned by the concept that the proposed stiffener spacing rule is employed as part of the design process. The proposed rule attempts to prevent inelastic web buckling in the intermediate length link end panels. Limitations and suggestions for future work are discussed.