Study On Flexural Behavior Of Ultra High Performance Concrete Beams With HRB600 Reinforcement

Ultra-high Performance Concrete(UHPC)has super-high compressive strength,high tensile strength,high toughness,high durability,and has a good application prospect in engineering.Considering the super-high compressive strength of UHPC,high-strength reinforcement is especially suitable for reinforcement structure design.HRB600 bar,as a high-strength hot-rolled ribbed bar,can give full play to both performance when used together with UHPC.In this paper,the bending behavior of UHPC beam with HRB600 bars is studied by combining theoretical analysis with experiments.The whole process analysis program is compiled to study the influence of reinforcement ratio,reinforcement strength,UHPC strength and beam height parameters on the bending behavior of UHPC beam.The calculation methods of cracking moment,short-term stiffness and bending capacity of UHPC beam are derived.The research results can provide a basis for structural design of UHPC beams.The main work and conclusions of this paper are as follows:(1)The HRB600 reinforced UHPC beams with different reinforcement ratios and protective layer thicknesses were designed and compared with HRB400 reinforced UHPC beams to study the flexural properties of UHPC beams.The test showed that the highstrength steel bar can effectively improve the bending capacity of UHPC beam.The bending capacity of HRB600 reinforced UHPC beam was 27.6% higher than that of HRB400 reinforced UHPC beam with the same reinforcing ratio and had better ductility.HRB600 bar and UHPC have better synergistic working performance,and the use of high-strength steel bar can reduce stiffness degradation and limit crack development to a certain extent.(2)Based on the sectional analysis method,the whole bending process numerical analysis program of UHPC beam was developed,which could better reflect the bending response of UHPC beam.The influence of different parameters(reinforcement ratio,reinforcement strength,UHPC strength,fiber content,fiber aspect ratio,beam height)on the bending behavior of UHPC beams was investigated.With the increase of reinforcement strength and reinforcement ratio,the bending capacity of UHPC beam increased significantly,but the bending contribution of UHPC materials in tension zone decreased accordingly.The bending contribution of UHPC in tension zone should be considered when the reinforcement ratio is low.The reduction coefficient k of uniform stress distribution increased significantly with the increase of fiber aspect ratio and the decrease of beam height.A calculation method of reduction coefficient k was proposed based on regression analysis.(3)The calculation formulas of cracking bending moment,short-term stiffness and bending capacity were deduced by analyzing the mechanical properties of UHPC beam at different stages and considering the bending contribution of UHPC materials in tension zone in combination with the test results.The bending database of UHPC beam was established and the SVM algorithm was used to predict the bending capacity and failure mode of UHPC beam.The predicted value was in good agreement with the test value.