One of the common issues in brace connections is the uneven stress distribution across the gusset edge (Richard 1986). In the case of a bracing connection welded to the flange of a member, which has significantly more rigidity than a connection to the web, the potential inability of the system to accommodate force distribution was observed (Hewitt and Thornton 2004). The development of a peak stress induced at some point across the welded connection might cause the weld to fail at the point where the stress is concentrated causing an unzipping of the weld and a progressive failure of the welded connection (Hewitt and Thornton 2004). Such a phenomenon has been confirmed in experimental studies as well (Lumpkin, Hsiao et al. 2012). To solve this issue, (Richard 1986) considered the ratio of peak over average of the stress distribution at the gusset-to-beam interface. Based on the results of this study, AISC required that the weld size be increased by 40 percent to ensure adequate force redistribution in corner gussets used for bracing members. This 1.4 factor used in weld design is called ductility factor. (Hewitt and Thornton 2004) performed a statistical analysis to Richard’s empirical results and reduced the ductility factor to 1.2. However, These studies are all limited to corner gussets in bracing members. This study evaluates the ductility factor value for chevron (middle) gusset plate connections. In order to do so, a group of 20 assemblies each consisting of a beam, rectangular gusset(s) with chavron V- and X-type bracing configuration, and the beam to gusset(s) weld connections are designed, and then modeled in a finite element software to check the stress distribution along the weld line. Finally, the value of the weld ductility factor for all of the assemblies is evaluated.
Key words: Braced frame, Chevron, Gusset plate, Connection stress distribution, Weld Ductility factor.
Hewitt, C. M. and W. A. Thornton (2004). "Rationale behind and proper application of the ductility factor for bracing connections subjected to shear and transverse loading." ENGINEERING JOURNAL-AMERICAN INSTITUTE OF STEEL CONSTRUCTION 41(1): 3-6.
Lumpkin, E. J., et al. (2012). "Investigation of the seismic response of three-story special concentrically braced frames." Journal of Constructional Steel Research 77: 131-144.
Richard, R. M. (1986). Analysis of large bracing connection designs for heavy construction. National Steel Construction Conference Proceedings.