Experimental Tests of Truss Bridge Gusset Plate Connections with Sway-Buckling Response

The collapse of the Interstate 35W bridge in Minneapolis, Minnesota, in 2007 brought into question the strength of large-size gusset plates in steel truss bridges. To provide new data on the behavior and strength of large-size bridge-type gusset plates, experimental tests were performed and are described in this paper. The research program focused on sway-buckling behavior and test variables included plate thickness, compression diagonal flexural stiffness, initial out-of-plane imperfection, and member load combinations. Unique to this test program was the direct consideration of different compression diagonal out-of-plane flexural stiffnesses on plate buckling behavior and capacity. Results showed that sway-buckling behavior and ultimate capacity were affected by initial out-of-plane imperfections of the plate and the out-of-plane bending stiffness of the truss compression diagonal. Results also showed that the effective length factor, $K$, a parameter used in present load rating guides, did not accurately predict sway-buckling capacity, and the Whitmore section approach may not be the best approximation for use in plate sway-buckling behavior. A stepped-column approach was shown to illustrate and predict the effect of the plate-member stiffness interaction on buckling capacity.