| Ultra-high Performance Concrete(UHPC)has relatively good mechanical properties,significantly improving the strength and durability,but it also increases the rigidity and shrinkage characteristics of the material,with limited ductility improvement.In addition,the steel fibers in UHPC are often distributed randomly,which cannot correspond to the adverse mechanical state of the beam members,and the UHPC members are still prone to brittle failure.If the reinforcement is designed,it is expected to avoid the above deficiencies,give full play to the excellent characteristics of UHPC materials,and improve the bearing capacity of components more efficiently.The analysis and experiment of the reinforcement of UHPC components are rare at present,and there is also a lack of general design specifications in the industry.Based on the existing research situation,this paper has carried out the following aspects of work:First,the material properties of UHPC were tested using the same curing block as the reinforced experimental beam,and the stress-strain curves of compression and tension were obtained.It was proved that UHPC has the characteristics of strain hardening,and the bridging effect of steel fiber improved its crack resistance.Through the bending performance experiment of 5 reinforced UHPC beams,the influence of the reinforcement ratio,the distribution of the main reinforcement and the diameter of the main reinforcement on the stress process,load-deflection curve,crack development and distribution of the beam body was investigated,and the stress process and failure mode of the experimental beam were analyzed.The results show that: HRB400 steel bar and UHPC beam good bonding performance;With the increase of the reinforcement ratio,the cracking load,yield load and cracking load of the members increased to different degrees,and the concrete strain at the bottom of the beam also increased under the cracking load.For the experimental beam with appropriate reinforcement ratio,the load-deflection curve changes gently,the mechanical performance of the beam is good,and the number and width of cracks are effectively controlled.The strain of concrete in the elastic section of the experimental beam satisfied the assumption of flat section.Secondly,the general finite element software ABAQUS was selected to build a numerical analysis model for 5 experimental beams,and the material parameters of the plastic damage model were determined.The ABAQUS interface is built by Pathon software,and the failure pattern of the model beam is displayed intuitively.In the finite element analysis,the load-deflection curve is in good agreement with the experimental curve,and the failure mode of the simulated beam is well matched with the experimental beam,which indicates that the finite element analysis can better simulate the stress state of the experimental beam.The cracking load,yield load and ultimate load of the UHPC beam are much higher than those of the C50 beam.Thirdly,the orthogonal analysis method combined with finite element model was used to analyze the yield strength of reinforcement,the reinforcement ratio of longitudinal reinforcement,the compressive strength of UHPC,the tensile strength of UHPC,the size of prestress and other parameters.The results show that the prestress and the tensile strength of UHPC have the greatest influence on the cracking load,the longitudinal reinforcement ratio and yield strength have significant influence on the yield load and ultimate load of the beam,and the compression strength of UHPC directly affects the failure load of the beam.Finally,the crack moment and ultimate bearing capacity calculation method of UHPC beam are studied.Considering the contribution of the tensile strength of UHPC to the bearing capacity,the corresponding calculation model and formula are modified based on the relevant research and the experimental results in this paper.In order to prevent the occurrence of overbar beam and under-bar beam,the limiting reinforcement ratio is derived. |
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