Refined Finite Element Analysis On UHPC Continuous Beams With High Strength Hot Rolled Bars Considering Internal Force Redistribution

Ultra High Performance Concrete(UHPC)is a new type of high performance cement-based composite material,which has the advantages of high strength,strong toughness and good durability.High-strength steel bar has high tensile strength and good ductility.When it is used together with ultra-high performance concrete,it can give full play to the excellent performance of both,improve the structural safety reserve,meet the requirements of sustainable development of buildings,and have a broad application prospect in the field of civil engineering.Considering the redistribution of internal forces in the design of concrete structure is helpful to alleviate the congestion of bearing reinforcement,save the amount of materials and facilitate the construction.Especially for UHPC structure,because its material cost is higher than traditional concrete,it is particularly important to consider the redistribution of internal forces in the design.Based on this,at present,the relevant design codes at home and abroad have specific provisions on the bending moment amplitude modulation amplitude of traditional concrete structures,but have not yet involved high-strength reinforcement and ultra-high performance concrete.Based on this,this paper carries out fine finite element analysis of UHPC continuous beams with high strength reinforcement,and focuses on the research of the flexural performance and internal force redistribution characteristics of UHPC continuous beams.The specific research contents are as follows:(1)The UHPC constitutive model proposed by domestic and foreign scholars is summarized,and the optimal UHPC constitutive model is selected by quantitative analysis of the stress-strain test curves of UHPC in tension and compression combined with the curve trend method.The finite element model of UHPC continuous beam is established,and the accuracy of the model is verified by combining with the experimental results in the literature,which provides a basis for the subsequent research on the internal force redistribution of UHPC continuous beam.(2)The fine finite element simulation study of 6 ultra-high performance concrete beams with high-strength reinforcement was completed,and the distribution of longitudinal reinforcement strain and section curvature was analyzed.The plastic hinge performance of UHPC continuous beams was investigated,and the calculation formula of UHPC equivalent plastic hinge length was established.It is found that with the increase of the yield strength of steel bars,the process of UHPC continuous beam from concrete in tension zone into tensile plasticity to tensile longitudinal reinforcement yield becomes longer.At the same time,the ultimate compressive strain of UHPC is significantly higher than that of ordinary concrete,and the plastic development section of UHPC structure becomes longer from the formation of plastic hinge to the occurrence of bending failure,and the ultimate bending moment and ultimate curvature of the control section increase.Therefore,the internal force redistribution of UHPC continuous beam is proposed to be divided into two stages of the study before and after the formation of plastic hinge.(3)The expansion parameters of 120 UHPC continuous beams with high-strength reinforcement were analyzed,and the influence laws of key factors such as the axial compressive strength of UHPC,steel yield strength,load form,span height ratio,ratio of reinforcement ratio of mid-span to mid-support control section,and relative compression zone height on the twostage moment amplitude modulating coefficient of UHPC continuous beams were studied.It is found that with the increase of concrete compressive strength,the height of the control section relative to the compression zone,the span height ratio and the beam section size,the moment amplitude modulation coefficients of the two phases all decrease.With the increase of steel yield strength,the moment amplitude modulation coefficient of the first stage increases,while the moment amplitude modulation coefficient of the second stage decreases.The moment amplitude modulation coefficients of the two stages increase with the increase of the ratio of reinforcement ratio between mid-span and mid-bearing.Based on the results of finite element analysis with expanded parameters and with the key parameters as independent variables,the fitting formulas of the bending moment amplitude modulation coefficient of the first stage and the bending moment amplitude modulation coefficient of the second stage of the continuous beam with high strength reinforcement and ultra-high performance concrete under different loading forms are established.(4)Compared with the ordinary concrete continuous beam,it is found that the redistribution of internal forces in the first stage of the ultra-high performance concrete continuous beam decreases,and the redistribution of internal forces in the second stage increases,and the total amplitude modulation coefficient of the ultra-high performance concrete continuous beam is slightly higher than the ordinary concrete continuous beam.Therefore,the amplitude modulation of bending moment should be improved in the plastic design of UHPC continuous beams considering internal force redistribution.