Tests and limit analysis of loop connections between precast concrete elements loaded in tension

This paper deals with loop connections loaded in tension. Such connections; also known as U-bar joints, are frequently used in practice to establish continuity between precast deck elements in steel–concrete composite bridges. The tensile strength of a loop connection may either be governed by yielding of the U-bars or by failure in the joint concrete. Only few investigations of the case of concrete failure can be found in the literature. This paper presents an experimental program dedicated to study loop connections critical to concrete failure. The results show that the ultimate load is influenced by important design parameters such as the overlapping length of the U-bars, the spacing between adjacent U-bars and the amount of transverse reinforcement. Knowledge about the parameters that have an effect on the failure of the joint concrete is important in order to avoid this failure mode in practice. The paper also presents an upper bound plasticity model, which is able to capture the experimental tendencies in a satisfactory manner. Finally, the paper includes discussions of how the presented research may be utilized in practice to design connections that are able to transfer the full yield strength of the connecting precast elements.