Transverse Modeling of Concrete Box-Girder Bridges for Prediction of Deck Slab Ultimate Load Capacity

Concrete box-girder bridges are one of the most commonly used bridge types owing to ease of maintenance and economy in construction. However, current design codes do not realistically consider the effects of haunches and web restraints on the strength enhancement of the top deck slab in the box-girder bridges. The purpose of this paper is to propose a rational model that can consider the effects of arching and haunches on the prediction of ultimate load capacity of deck slabs in concrete box-girder bridges under vertical loading. A rational frame model for the transverse direction of box girders that considers the effects of rigid joints and nonprismatic elements was formulated in this study. The flexural strength enhancement of the upper slab from the restraints of webs and arching action also was derived. To verify the model, a comprehensive experimental program was set up, and several full-scale concrete box girders were tested. The displacements and strains of steel bars and concrete were measured for test box girders during the vertical loading process. It was found that the cracking patterns and failure modes of box girders vary greatly depending on the existence and size of haunches. The present test results also indicate that an increase in haunch size increases the ultimate load capacity of the deck slab of a box girder greatly. The load capacity of a haunched deck slab is more than two times greater than that of the deck slab without haunches depending on the size of haunches. This effect is taken into account in this analysis through the consideration of arching action for the upper slab with various haunch sizes. Comparison of the proposed theory with test data shows good agreement on the ultimate loads and displacements. This study indicates that the theory without considering arching action greatly underestimates the ultimate load capacities of deck slabs in box-girder bridges. Therefore, the effects of haunches and arching action must be considered realistically for more advanced and economical design of box-girder bridges.