DIAGONAL ERECTION BRIDGING FOR OPEN WEB STEEL JOISTS WITH FLUSH FRAME CONNECTIONS

Open web steel joists are highly slender structural members that are susceptible to lateral-torsional buckling before bracing is installed. The stability of joists needs to be properly assessed to ensure safety and efficiency during erection. Current practice for joists is based on a strength equation derived by Minkoff in the 1970s. This equation was derived for the common case of joists with bearing seat connections. Flush frame connections for joists have been recently developed. These connections are similar in form to single-plate shear connections and can provide more restraint than bearing seat connections. With more restraint, less bracing may be required, however, the magnitude of the benefit is unknown. The objective of this research is to quantify the strength of unbraced open web steel joists with flush frame connections and to modify the Minkoff equation to improve its accuracy for joists with flush frame connections. Physical testing of four joists sizes and a variety of connection details, making up 60 different configurations, was conducted. The joists with flush frame connections supported more load than the joists of the same designation with bearing seat connections in almost all cases. Based on the experimental results, a modification to the Minkoff equation, specifically a new effective length factor for joists with flush frame connections, is proposed. The proposed modification will enable engineers to preserve the efficiency of open web steel joists while also ensuring safety during erection.