Performance of in situ stitches in precast concrete segmental bridges

Abstract

In-situ concrete stitching with subsequent prestressing is often used in construction to join precast concrete segments together. An example of 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 in this area has been done. 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 level for members with in-situ stitches while no cracking is observed elsewhere. The cracks widen extensively as load level increases and can become detrimental to the serviceability of member. Such members should be designed such that the joints are subject to no tension under service load.