SEAOC 2011 CONVENTION PROCEEDINGS 1 High-Strength Brace Connectors for use in SCBF and OCBF Carlos de Oliveira, President and CEO Cast Connex Corporation Toronto, Canada Constantin Christopoulos, Associate Professor Dept. of Civil Engineering, University of Toronto Toronto, Canada Jeffrey A. Packer, Professor Dept. of Civil Engineering, University of Toronto Toronto, Canada Abstract Innovative cast steel high-strength connectors for round hollow structural section brace members have been developed at the University of Toronto for use in Special and Ordinary Concentrically Braced Frames (SCBF and OCBF). The standardized connectors, now available through Cast Connex Corporation under their High-Strength Connector line of products, have been applied in the construction of various seismic-resistant steel braced frame buildings in the United States and Canada. At one end, the connectors are designed with a circular shape and preparation to allow for complete joint penetration shop welding to a range of round tubular braces of a given outer diameter for the full development of their expected strength. At the other end, the connectors are shaped such that a bolted double shear connection or longitudinal fillet welds can be used for connecting the shop-welded brace-connector assembly to conventional gusset plates in the field. This paper describes the mechanical properties of the cast steel material comprising the connectors, provides an outline of the design rationale for the connectors meeting the AISC Seismic Provisions’ requirements for SCBF and OCBF brace connections, and provides a summary of the full-scale structural testing that has been conducted to validate the connector design philosophy. Introduction Special and Ordinary Concentrically Braced Frames (SCBF and OCBF) are an efficient and popular choice for the lateral force resisting systems of mid- to low-rise seismic-resistant steel building frames. When lateral forces are applied to these structures, the diagonal bracing members of the braced frame are subjected to predominately axial loading. As Hollow Structural Section (HSS) members are the most economical structural shapes for carrying compressive loading, and given the wide range of section sizes that are readily available in the United States, it is not surprising that HSS are the typical brace member of choice in these buildings. Statically loaded HSS braces are typically connected to the beam, column, or beam-column intersection via slotted HSS- to-gusset connections, and the braces are typically welded in the field to the single gusset plate at each end of the brace. Design of these connections for static axial loading accounting for shear lag effects has been studied by a number of researchers (British Steel, 1992; Korol et al., 1994; Zhao and Hancock, 1995; Cheng et al., 1996; Zhao et al., 1999; Wilkinson et al., 2002; Ling, 2005; Willibald et al., 2006; Martinez-Saucedo et al., 2006; Martinez-Saucedo et al., 2008; Martinez-Saucedo and Packer, 2009); these statically loaded connections can be readily detailed according to prevailing design standards. However, during a design level seismic event, the brace members in SCBF and OCBF are intended to cyclically yield in tension and buckle in compression, and as such the connections at each end of the brace must be appropriately capacity designed and detailed to ensure this behavior. If brace end connections are inappropriately designed, detailed, or fabricated, the connections can be prone to premature failure, as witnessed during post-earthquake reconnaissance and in laboratory testing (AIJ, 1995; Bonneville and Bartoletti, 1996; Tremblay et al., 1996; Yang and Mahin, 2005; Fell et al. 2006). Failures in these types of connections in earthquakes typically occur due to a concentration of inelastic strain at the reduced section of the HSS-to-gusset connection. As a result, AISC