Introduction of Transition Zone Design for Bridge Deck Link Slabs Using Ductile Concrete

This paper presents an innovative approach to designing the transition zones between concrete deck slab segments and an adjacent highly deformable link slab on a steel girder composite bridge deck. (A link slab provides a special class of jointless bridge for which only the bridge deck is made continuous rather than both the deck and girders). The transition zones represent a fraction of the ends of the link slab introduced to divert stress from the potentially weak link slab/deck slab interface. The link slab studied herein is built with an engineered cementitious composite (ECC), an ultra ductile concrete, adopted in a recent demonstration project in Southeast Michigan. Conventional design of concrete link slabs leaves the old/new concrete interface as the weakest part of the bridge deck system. Due to the presence of a link slab debond zone (part of the link slab is debonded from bridge girder to provide hinge flexibility), this interface also experiences high stress concentrations. In addition, the effectiveness of the link slab design depends on the integrity of the interface so that imposed rotation and tensile deformation will be accommodated within the highly deformable ECC link slab. The basis of the suggested approach is to isolate the concrete/ECC interface away from the structural interface between the debond zone and composite zone to prevent interfacial cracking. The shear studs and lap-spliced reinforcement located within transition zones facilitate load transfer between the concrete deck and the ECC link slab. These modifications are expected to cause a shift of the stress concentration from the concrete/ECC interface to the bulk part of the ECC link slab. In support of this new design concept, experimental tests are carried out on the behavior of the ECC link slab-bridge deck-girder connection. Detailing of the transition zone, that is, spacing of shear stud and development length/lap splice length requirement is then laid out in a design procedure based on results of shear stud/ ECC pushout and reinforcement pullout tests.