Overview of the development of design recommendations for eccentrically braced frame links with built-up box sections

Among the new additions to the 2010 AISC Seismic Provisions are design requirements for eccentrically braced frame links with built-up box sections. Such links do not require lateral bracing in many cases because built-up box shapes have superior lateral torsional stability relative to wide flange sections. The 2010 Seismic Provisions include requirements for built-up box link flange width-to-thickness ratio and other important design considerations. However, the limits on web width-to-thickness ratio default to those used for built-up box beams or columns and are inadequate for links with large inelastic shear and compression strains. Such limits are important for preventing web buckling under shear and/or flexural compression. This paper presents an overview of research on the design and behavior of links with built-up box sections, including the development of recommendations for web width-to-thickness limits and corresponding web stiffener spacing requirements and flange width-to-thickness limits for these link sections. The highlighted research program included derivation of design requirements based on plate buckling considerations; a full-scale, single-story eccentrically braced frame test; a parametric study on the impact of link crosssectional parameters on link inelastic rotation capacity; and a series of large-scale tests on isolated links.