Experimental Study on the Flexural Performance of Precast Segmental UHPC Thin-Walled Box Girder Bridges

Ultrahigh-performance concrete (UHPC) thin-walled box girder systems (UTWBGSs) offer a promising alternative to traditional prestressed concrete box girder bridges. This system addresses two persistent issues in long-term bridge operation, excessive deflection and cracking, and also improves the spanning capacity of prestressed concrete box girder bridges. Based on an actual UTWBGS bridge with a single span of 102 m, tests have been carried out on five 3:20-scale equivalent precast UHPC segmental I-beams with different epoxy joints for exploring the overall flexural behavior of such structures. These specimens include one monolithic specimen with two fake joints and four segmental specimens with distinct epoxied joint configurations. Among the segmental specimens, three contain two joints each (plane, large tooth key, and small tooth key types), while the remaining specimen featured only a single small tooth key joint. The failure modes, cracking behavior, and stress responses of prestressed tendons have been documented. Experimental results indicate that the UHPC segmental I-beam mainly experienced failure because of the epoxy adhesive, resulting in joint opening at the joint location, while there are no cracks in the UHPC matrix within the segments, distinguishing them from the conventional concrete segmental box girder with epoxied joints. Notably, with the breaking of longitudinal prestressed tendons at the joints, the monolithic UHPC I-beam shows a different mechanical behavior (load drop occurring in the loading test) compared to similar UHPC T-beams reported in a previous study. Based on the experiments, a simplified method for calculating the bending capacity of UTWBGSs is proposed for engineering applications, and the results show a good agreement with the tests. In addition, a model for analyzing the short-term stiffness of the UTWBGS is also proposed, which can accurately predict its nonopening and opening stiffness. This study provides a reference for the promotion and development of the UTWBGS and enriches the computational theory of externally prestressed UHPC segmental beams with adhesive joints.