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An experimental program investigating the flexural behavior of an innovative dovetail ultra-high performance concrete joint for connecting precast ultra-high performance concrete slabs in composite bridges is reported in this study. Test parameters included interface treatment method, joint material, reinforcing bar overlapping form, and prestressing level. Specifically, a new steel wire mesh interface treatment was proposed, which could generate an additional fiber-bridging mechanism in the joint surface. An enhancement of 17.4%, 20.1%, and 50% on flexural cracking strength, ultimate strength, and ductility were obtained by using the steel wire mesh. Joint material showed no significant influence, while prestressing had obvious influence on the flexural behavior of ultra-high performance concrete joints. The post-cracking behavior, ductility performance, and stiffness degradation of the tested specimens were analyzed. Good deformability was obtained for the jointed ultra-high performance concrete slabs as the ratio of deflection to span was about 1/50 at failure. The post-cracking stiffness was retained at about 90% of the initial stiffness, while the ultimate stiffness was retained at about 10% of the initial stiffness. The research findings are useful in popularizing and applying the proposed innovative dovetail ultra-high performance concrete joints in composite bridges.

This article presents an experimental and theoretical investigation on the shear behavior of fiber-reinforced ultra-high-performance concrete beams reinforced with high-strength steel. The test parameters included the fiber volume fraction, fiber type, and stirrup ratio. The test results indicate that the shear failure in ultra-high-performance concrete beams is not brittle and catastrophic but has ductility characteristics. A moderate quantity of stirrups can significantly improve the shear behavior of ultra-high-performance concrete beams, as reflected in the thorough propagation of cracks in both shear span and pure bending zone. The depth of the compression zone considering concrete tension was derived based on the deformation compatibility and force equilibrium equations for both serviceability limit state and ultimate limit state. The comparison of the proposed method and classical beam theory shows that the concrete tension should not be neglected in the serviceability limit state analysis. After cracking, the concrete tension can be neglected for simplicity when the beam is heavily reinforced and should be considered when the beam is lightly reinforced. Then, a shear strength model was established based on Rankine’s failure criteria, the truss model, and Association Francaise de Génie Civil-Sétra. Finally, the proposed shear strength equation was verified by the test results and compared with other shear strength equations.

This paper presents a performance-based evolutionary topology optimization method for externally prestressed concrete(EPC) beams in automatically generating optimal strut-and-tie models using the finite element method. The concrete and steel bar elements with least contribution to the stiffness of the EPC beam are removed by calculating the element virtual strain energy. Load transfer mechanism of EPC beam is characterized by remaining elements. The optimal strut-and-tie model is determined from the topology history. A theoretical formula of the shear strength is derived from optimal strut-and-tie model for EPC beams. The model predicts possible modes of failure, which may be broadly classified into shear-type failure and flexural-type failure. 9 EPC beams were casted in place to evaluate the validation of the proposed method. The predictions of the method are compared with the 9 specimen and other available test results of EPC beams from literatures. Case studies are conducted and compared with the resul...