UFC is one of the cementitious materials which have outstanding properties such as more than 200 MPa compressive strength, high ductility and durability. The permanent formwork for RC structures is one of the promising applications of UFC. This research is aimed to investigate the shear behavior of RC beams using a U-shaped UFC permanent formwork. Eight RC beams using a U-shaped UFC permanent formwork were tested by four-point bending test. The experimental parameters were the presence of shear keys at the internal surface of a UFC U-shaped permanent formwork, presence of screws and bolts, thickness of formwork, shear span to effective depth ratio and presence of stirrups. The experimental results indicated that a U-shaped UFC permanent formwork enhanced the shear capacity of RC beams more than twice compared to normal RC beams. In addition, the shear resistance mechanisms were investigated. By using a UFC formwork with shear keys and screwed bolts, the UFC formwork intercepted widening of diagonal cracks inside a RC part. Finally, the shear carried by a UFC permanent formwork was investigated. The proposed calculation method can provide a good agreement with the experimental values.
The experimental results and predictive equation for shear capacity of Perfobond strip (PBL) joint connection with cast-in-place UFC to develop UFC-PC hybrid girders are presented in this paper. The UFC-PC bridge consists of PC segment at both ends and UFC segment at the middle of the span. Push-out test of twelve specimens was conducted. The experimental parameters were thickness of PBL, diameter of the hole of PBL, diameter of transverse rebar, prestressing stress on connection part, and the ratio of spacing to diameter of PBL. The experimental results indicated that PBL with cast-in-place UFC connection was sufficient to transfer the shear forces between the two segments. The contributions to shear capacity in each term were clarified. In addition, the shear resisting mechanisms were investigated. By inducing prestressing stress on the connection part, the shear capacity drastically increased due to the friction resistance. Finally, the shear capacity equation for PBL with cast-in-place UFC connection was proposed. The proposed calculation method can provide a reasonable agreement with the experimental results.
The ultra high strength fiber reinforced concrete (UFC) is an advanced cementitious material which grants the high performances in strength, durability, and ductility. Because of these high performances, in this study, it was applied into the new idea for shear strengthening to RC beams, namely the post-tensioned UFC panel. It is the prefabricated UFC panel prestressed by some prestressing force. Three parameters (i.e., the number of post-tensioned UFC panel, the amount of prestressing rods, and the prestressing level in the UFC panels) were studied from eight strengthened beams for investigating the shear strengthening performance. All specimens were subjected to four-point bending. The results of the strengthened beams and the non-strengthened beam revealed that the strengthening by post-tensioned UFC panel increases the shear capacity, stiffness, and ductility of the beams. Moreover, the prestressing level also influenced the delay of the initial cracking load and the yielding of stirrups. Finally, the shear capacity carried by the post-tensioned UFC panel was proposed by using the force equilibrium along the assumption of imaginary diagonal crack.
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