Reducing damage to concrete stitches in bridge decks

Abstract

In bridge widening projects, it is a common practice to provide a monolithic connection between the existing and new decks by casting an in situ concrete stitching slab. Due to the difficulties associated with complete closure of the bridge, traffic flow has to be maintained on the existing deck. As a result, the existing deck will deflect under traffic load and the concrete stitching slab will be subjected to differential deflection, which is cyclic in nature. Such cyclic differential deflection hinders strength development of the concrete and may affect the structural integrity of the stitching slab. Some possible methods of reducing the differential deflection so as to mitigate damage to the curing concrete stitches have been proposed, but no systematic comparative studies have been carried out. These methods include traffic restriction, provision of temporary shear connections, provision of temporary propping and segmental concrete stitching. This paper evaluates the relative effectiveness of these mitigation measures as well as their different combinations by conducting grillage analysis of the widening bridge deck at various stages of construction. Based on the results, it is advocated that among these, the combination of temporary shear connection and segmental concrete stitching should be the most practicable and effective.