Composite Action of Precast Panel Bridge Decks in Negative Moment Regions

A one third scale composite steel concrete bridge model with a precast deck was tested under negative moments to investigate the behavior of the structure before and after cracking of the deck. The model was simply supported and an upward concentrated load was applied at midspan to develop negative moments while the supports were restrained against uplift. The experiment included loading sequences before and after cracking of the concrete deck. The first was used to determine the section properties of the model, and the second to study the loss of composite action due to cracking of the concrete deck. The results show that the effects of the epoxy grouted joints between the deck panels on the stiffness of the structure are not significant, and that the behavior of the model under positive moments is different from that under negative moments due to the lower modulus of elasticity of concrete in tension. Cracks in the deck were observed first at the joint locations even though these were not the most highly stressed regions. A loss in composite action was observed in a region of length equal to about 18 deck thicknesses due to the development of a crack (a).