Stresses in the Negative Moment Region of Composite Steel Bridges

Summary

In a simply supported composite bridge girder the concrete is in compression over the full length of the bridge, whereas in a continuous multispan bridge some regions of the bridge are subjected to negative bending moment, in which case the concrete goes into tension. With respect to fatigue behavior of stud shear connectors, one key difference between placing studs in the positive and negative moment regions is the stress state of the base metal of the beam flange. The fact that the beam flange is in tension at the base of the studs in the negative moment region raises questions about whether this affects their fatigue endurance. This report summarizes the research behind the fatigue design provisions for shear connectors in the negative moment region in the American Association of State and Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Specification.