Performance of in situ stitches in precast segmental bridges

In situ concrete stitching with subsequent prestressing is often used in construction to join together precast concrete segments. An example of an application is the stitching of the approaching decks of precast segmental bridges constructed using the balanced cantilever method. The relatively narrow stitches used in segmental bridges are often provided with nominal reinforcement only. Therefore, the in situ stitch is a location of potential weakness, but relatively little work has been done in this area. In light of this, extensive experimental and numerical studies on the behaviour of precast concrete members with in situ concrete stitches have been conducted. The effects of stitch width, prestressing force, concrete strength, bonding of tendon and provision of shear keys on the performance of such members are presented in this paper. Unlike members that are continuously cast, cracking initiates along the construction joint between the precast segment and the stitch at low load levels for members with in situ stitches, while no cracking is observed elsewhere. The cracks widen extensively as the load level increases and can become detrimental to the serviceability of the members. Such members should be designed so that the joints are subject to no tension under service load.