Fatigue evaluation of longitudinal U-bar joint details for accelerated bridge construction

Continuous longitudinal U-bar joint details for accelerated bridge construction are investigated. Four pairs of full-scale slabs connected by a U-bar detail with one of the selected closure-pour materials were tested under static and fatigue loadings. The loading demand necessary in the slab fatigue testing is determined on the basis of 3D finite-element (FE) parametric studies. Test results were evaluated on the basis of flexural capacity, curvature behavior, cracking, and steel strain. The fatigue loading was found to have little influence on the U-bar joint behavior. In general, crack widths were small at the service load level. No debonding between the slab and the joint was noticed. The joint moment capacity can be calculated on the basis of the assumption that U-bars were continuous reinforcement through the joint zone (i.e., not staggered as in actual specimens) reaching their yield strengths at ultimate. The actual moment capacity depends on the interaction between the closure-pour material and steel as well as the steel arrangement. Because the closure-pour material is cast-in-place and has a relative short curing time for the purpose of accelerated construction, it is very important to control its strength variation. On the basis of these tests, the U-bar joint detail is a viable connection system for the longitudinal joint in bridge decks.