In order to improve the failure state of over-reinforced beams and enhance their ductility, an innovative reinforcement method was proposed by adding an ultrahigh performance concrete (UHPC) layer on the top surface of the over-reinforced beam to take advantage of the high compressive strength of UHPC. The numerical simulation method was used to carry out the research. The validity of the finite element model was verified by comparing it with the experimental results, and the effectiveness of the new reinforcement method was verified by comparing it with the calculation results after adding the UHPC layer. Then, a detailed parameter study was carried out, including the thickness of the UHPC layer, the cross-section area of longitudinal tension rebar, and concrete strength. The load-deflection curve, flexural bearing capacity, and deflection ductility coefficient were studied. The results show that the bearing capacity of the UHPC-reinforced over-reinforced beams is significantly increased by 88.1%. And the stiffness and ductility of the beams are also significantly increased, with the ductility coefficient reaching 23.85. In addition, flexural bearing capacity increases with the thickness of the UHPC layer and sectional area of longitudinal tension rebar. Finally, a prediction model for the flexural bearing capacity of UHPC layer-reinforced over-reinforced beams is proposed, which further verifies the effectiveness of this method.

UHPC is different from ordinary concrete for mechanical properties. To study the stress state of stud connector when UHPC is used to strengthen RC beam and its influence on bearing capacity of the strengthened beam, in this paper, ABAQUS was adopted first to simulate the push-out test of  stud to verify  accuracy of the finite element model. The nonlinearity of materials and contact conditions was considered in the model, and then three parameters including concrete strength, stud length and stud diameter were studied. Results showed the finite element model established by surface to surface contact method was possible to simulate the force and failure of the stud connector. UHPC could improve the  bearing capacity of the stud specimens obviously, and the length of stud had little effect on bearing capacity of stud while failure of the stud may occur if length of the stud was too small. The increase of stud diameter could improve bearing capacity of elastic working stage.