Study On The Basic Performance And Calculation Theory Of Reinforced UHPC Members

In this dissertation,the basic mechanical performance and calculation theory of reinforced UHPC members are well studied.The direct tensile properties of UHPC at the material level,the mechanical performance and calculation theory for bearing capacity of reinforced UHPC members subjected to direct tensile load,the mechanical performance of reinforced UHPC flexural members,the calculation theory for crack width of reinforced UHPC members,the calculation method for shear bearing capacity of reinforced UHPC flexural members,and the calculation method for local compression bearing capacity of reinforced UHPC are mainly discussed.The main work and innovation of the thesis are as follows:(1)Eight groups of UHPC dumbbell-shaped specimens were designed and tested under the direct tensile load at the material level.The influence of fiber aspect ratio,fiber shape,fiber hybrid,and fiber presence on the direct tensile properties of UHPC materials were systematically studied.Based on the structural design requirements and convenient for practical engineering use,a method for classifying UHPC axial tensile properties based on nominal c tensile strength is proposed.Based on the test results,a tensile constitutive model of UHPC material is proposed with two parts,which consists of a bilinear stress-strain curve model based on the initial cracking stress,an exponential function or a linear function stress-crack width curve model based on fracture energy.The model parameters can be directly calibrated by the experimental data without parameter fitting,and the form is simple and easy to use.(2)Five groups of reinforced UHPC dumbbell-shaped axial tension members were designed and tested.The effects of reinforcement ratio,fiber orientation and chemical treatment of fiber interface on the mechanical performance of reinforced UHPC axial tension members were systematically studied.Then,based on the test results of reinforced UHPC axial tension members,the calculation theory for bearing capacity of reinforced UHPC axial tension members considering the tensile contribution of UHPC was established,and its applicability was verifed.Finally,based on the analysis of axial tensile hardening and softening properties of reinforced UHPC axial tensile members after yielding,the prediction method of axial tensile hardening performance based on axial tensile performance factor and its limit reinforcement ratio are proposed.(3)The four-point bending tests of 25 reinforced UHPC beams were designed and completed.The effects of reinforcement ratio,reinforcement diameter,cover thickness,fiber content,fiber aspect ratio and fiber hybrid on the mechanical performance of reinforced UHPC flexural members were systematically studied,and a large number of test data samples were accumulated for the following calculation theory for crack width of reinforced UHPC members.(4)Based on the basic assumption of UHPC structure calculation,the numerical calculation method for steel stress of flexural members is established,and the simplified formulas of steel stress of UHPC axial tension members and flexural members are deduced and corrected,and its applicability is verified.Then,based on the experimental data of Chapter 3 and Chapter 4,the calculation formulas for crack spacing and crack width in French NF P18-710,European MC 2010,Italian CNR-DT204,RILEM TC 162-TDF and CECS 38 : 2004 are evaluated and analyzed.Finally,the calculation method for UHPC crack width suitable for flexural members,axial-tensioned members and eccentric-tensioned members is proposed,and the relevant test verification is carried out.(5)The shear test database of UHPC beams with a total of 524 was established.The calculation formulas of shear capacity of concrete beams in French NF P18-710,Swiss SIA 2052,Japanese JSCE-2006,GB 50010-2010,CECS 38: 2004 and DBJ 43 /T 325-2017 were evaluated and analyzed.On this basis,the shear bearing capacity coefficients of inclined section UHPC matrix and steel fiber considering the influence of shear span ratio and steel fiber are proposed,and the calculation formula of shear bearing capacity of NF P18-710 in French UHPC code is modified and simplified.(6)A database of UHPC local compression tests with a total number of 177 was established,and the calculation formulas of local compression bearing capacity in French NF P18-710,CECS 38 : 2004,DBJ 43 / T 325-2017 and JTG 3362-2018 were evaluated and analyzed.On this basis,the correction coefficient of UHPC local compression and the influence coefficient of indirect reinforcement considering the influence of concrete strength and steel fiber are proposed,and the calculation formula of local compression bearing capacity in JTG 3362-2018 specification is revised.