Testing a composite box-girder bridge with precast decks

In order to design continuous composite bridges with full-depth precast decks, several factors should be considered, and confirmed through experiments: details of connections, serviceability of cracking and inelastic behaviour. After reviewing previous experiments, an experiment was executed with a steel box-girder bridge model having two spans of 10 m each. Because there is no reinforcement at the transverse joints except prestressing tendons, a design criterion for the prevention of cracking at the joints is not to allow tension at the joints under service loadings. In this paper, a major interest is in the behaviour of a composite section in a negative moment region. Therefore the elastic and inelastic behaviour of the model was carefully observed to provide proper design bases. In particular, cracking load, crack width and moment curvature of composite sections were investigated. The validity of the stiffness of the concrete slab in the negative moment region is discussed in terms of serviceability and ultimate limit states. After cracking at the joints, the flexural behaviour of a beam was observed carefully to estimate tension stiffening effects of the tendon and moment redistribution. Test results showed that uncracked section analysis for the concrete slab in a negative moment region could be used for serviceability, and a cracked section for ultimate limit states.