Experimental study on open box bridges with precast decks

For the construction of open-topped steel box bridges, precast decks could be a very competitive choice in terms of the formwork for concrete slab casting. However, precast decks without reinforcement at transverse joints between precast slabs should be designed to prevent the initiation of cracking at the joints, because the performance of joints is especially critical for the integrity of a structural system. Several prestressing methods are available to introduce proper compression at the joints, such as internal tendons, external tendons and support lowering after shear connection. In this paper, experimental results from two continuous composite bridge models with precast decks are presented. The models have two spans and were loaded statically at each midspan. Internal tendons were used for one model and internal tendons and external tendons were used for the other model. Judging from the tests, precast decks over an internal support, which are in the negative moment region, have the whole contribution to the flexural strength of the composite section under service loads if appropriate prestressing is introduced. Cracking loads and patterns were observed and compared with calculated values. Moment-curvature relations for the models, which were obtained from strain data, are presented and discussed.