Stability of laterally unsupported shear links in eccentrically braced frames

Abstract

I-shaped links in eccentrically braced frames (EBFs) are susceptible to lateral or lateral torsional buckling when subjected to cyclic link rotations. Lateral bracing should be provided at the ends of the I-shaped links in order to prevent these failures. Requirements for such braces are available in widely used design specifications such as the AISC Seismic Provisions for Structural Steel Buildings (AISC341-16) and EC8. These requirements limit the use of I-shaped links in bridge piers and elevator shafts. A combined experimental and numerical study was undertaken to investigate the behavior of laterally unsupported I-shaped links under cyclic loading. The experimental study consisted of testing of six nearly full-scale EBFs where the link length, link length ratio, and presence of lateral supports were considered as the prime variables. The test results demonstrated that short links with link length ratios less than 1.22 can experience inelastic link rotations greater than the codified limit of 0.08 rad even without lateral bracing. A numerical parametric study was conducted to develop more generalized design recommendations for laterally unsupported I-shaped shear links. Stability of one-story one-bay EBFs was studied using geometrically and materially nonlinear finite element analysis including imperfections. The numerical results showed that I-shaped links without lateral bracing can provide a stable response when the link length ratio is less than 1.15. In addition to this limit, the ratio of the elastic critical buckling capacity to the plastic shear capacity should be greater than 3.5 and 2.5 for links with and without axial force, respectively.