| When the use function of the building structure changes,resulting in the increase of the required bearing capacity,etc.,the reinforcement ratio of the beam will increase,so that the situation of over-reinforcement may occur.When the use function of the building changes,resulting in an increase in the load,and the section size is limited,there will be a phenomenon of overbar.With the increase of the service time of the building structure,the strength of concrete will decrease,which will lead to the phenomenon of overreinforcement.When the concrete pouring strength is insufficient,there will be the situation of over-reinforcement,and so on.Because of the low strength of ordinary concrete,the traditional strengthening method of enlarging section is not effective.High ductility concrete(HDC)is a kind of cement matrix composite material with low fiber content.High ductility concrete is characterized by high ultimate compressive strain,high ductility,strain-hardening and multi-fracture development.Ultrahigh performance concrete(UHPC)is a kind of cement matrix composite material with high strength and toughness.Using high ductility concrete to reinforce concrete beams can change the failure mode of concrete beams and significantly improve their bearing capacity and deformation capacity.Therefore,this paper mainly studies the flexural behavior of overreinforced concrete beam strengthened with high ductile concrete,including the following aspects:(1)Considering the effects of reinforcement ratios,reinforcement materials,reinforcement thicknesses and reinforcement methods on the flexural behavior of the reinforced specimens,12 specimens were designed,which were 3 unreinforcement specimens,2 concrete reinforcement specimens,5 HDC reinforcement specimens and 2UHPC reinforcement specimens.Crack pattern and failure modes were noted,and deflection behavior and failure loads were measured by two-point symmetrical loading test.The test results showed that the use of high ductility concrete for the compression side of over-reinforced concrete beams to change their failure mode to ductile failure.Over-reinforced concrete beam strengthened with high ductility concrete significantly improves the flexural capacity and deformation resistance of the members.Overreinforced concrete beam strengthened with ultrahigh performance concrete improves the flexural capacity and deformation resistance of the member to a certain extent.(2)Based on the assumption of flat section,the theoretical calculation method and simplified calculation method for the bearing capacity of over-reinforced concrete beams strengthened by HDC/UHPC are proposed.The calculated values of the two methods are in good agreement with the experimental values.The calculation formula of the height of the relative compression zone of the reinforced specimens and the calculation formula of the thickness of the reinforcement layer are proposed.(3)According to the deformation mechanism of the beam,combined with the calculation method of the beam curvature and the equilibrium equation of the positive section force,the mid-span deflection values of the specimens under the four conditions of cracking,yielding,peak and limit are calculated.The calculated values are in good agreement with the experimental values.Based on deformation of the specimens strengthened by HDC,the calculation method of the thickness of the reinforcement layer is studied. |
