ABSTRACT

The paper investigates joining an existing prestressed bridge deck to a new deck monolithically. This phenomenon is investigated on one of the Mhloti River Bridges, north of Durban. The existing Mhloti bridge consists of a continuous 282.5 m long prestressed box girder deck. The new deck widening is also a prestressed box girder deck but of differing cross section to the old deck. Both decks have or will undergo creep and shrinkage which will lead to shortening of the decks with time. The existing deck which was completed in 1988 has already undergone most of its shortening due to creep and shrinkage. The new deck, on the other hand, has undergone only limited creep and shrinkage and will shorten at a much higher rate than the existing deck. This will cause restrained differential movement between the two decks in the longitudinal direction. As the two decks have differing movements longitudinally it is important that the connection between these two decks be investigated in detail. This paper investigates the possibility of connecting the two decks via an in situ concrete slab. The main conclusion of this paper is that a 280 m cast in situ slab between the new and old box girder decks connected monolithically is feasible. The construction of the widening was completed in 2015 so that actual performance of this construction technique is reported on.