Testing And Modeling Flexural Behavior Of A Large-scale Prestressed UHPC Tee Beam

Ultra-high performance concrete(UHPC)exhibits excellent mechanical properties and durability.UHPC offers a solution to build lighter weight bridge with lower creep,less deflection under longterm action and better durability.Based on the flexural test of the prestressed UHPC beam,the mechanical behavior of the beam and the principle of the rational design was discussed.The main research carried out in the thesis and its conclusions are as follows:(1)The flexural test of a large-scale prestressed UHPC tee beam was conducted to obtain the main test results,which indicated that the UHPC beam possessed great bending behavior and crack performance.The crushing of the UHPC of the top flange indicated the failure of the beam while the tendons didn't rupture.The ductility of prestressed UHPC beam is better than the ordinary concrete beam.(2)Combined with the existing research findings,the tensile consititutive model was modified based on the results of the flexural test.The tensile property of UHPC was considered to improve the calculation method of the crack load and ultimate bending moment,which predicted the ultimate capacity well.The analysis results indicate that the tensile plastic of UHPC should be considered when calculate the crack load according to the formula in the code of the bridge design of China.The tensile property makes limited contribution to the ultimate bending capacity of UHPC.(3)If the plane sections remain plane,a nonlinear analysis based on the finite stripe method was conducted.The analysis results agree with the test results of this paper and others.Then,the influence of the reinforcement ratio,tensile stress and high-span ratio on the flexural performance of the structure was discussed.The results show that:Increasing the area of prestressed tendon properly can make full use of the ultra-high compressive strength of UHPC and effectively improve the cracking bending moment and the ultimate bending capacity of the UHPC beam.(4)Based on the flexural test results of the UHPC beam,the concrete damage plastic finite element model was set up to study the mechanical properties of the prestressed UHPC beam.Analysis results are in good agreement with the test results.The influence of the parameters,including the depth-span ratio,reinforcement ratio,tensile stress,compressive strength and tensile strength,on the flexural performance was investigated.Main conclusions are as follows:The finite element model based on CDP model can simulate the flexural performance of the prestressed UHPC beam.Improving the ratio of reinforcement can lead to the significant improvement of ultimate bearing capacity and lower ductility.The improved ability for crack resistance and higher ductility can obtained by improving the tensile stress in the prestressed tendon.Higher compressive strength had no effect on the elastic and cracking behavior,but can effectively increase the ultimate displacement.Improving the tensile strength can effectively improve the crack resistance and ductility of member,and the limit bearing capacity is improved.To rational design the prestressed UHPC beam,it is suggested to determine the range of the reinforcement ratio based on the formula in this thesis.