| Steel-concrete composite beams have been widely used due to good force performance,but there are still problems such as easy cracking of wing plates in the negative bending moment area and buckling of steel boxes.In view of the above problems,this paper proposes a new structural form of ultra-high performance concrete(Ultra-high Performance Concrete)-narrow steel box composite beam,which improves the problem of easy cracking of the wing plate in the negative bending moment region by replacing the ordinary concrete part in the wing plate with UHPC,and at the same time,the steel box is partially filled with UHPC without steel fiber to prevent the buckling of the steel box.In this paper,a total of 8 UHPC-narrow steel box composite beams and 1 ordinary concrete-narrow steel box composite beam are designed for negative bending moment loading test,and the overall force performance of the composite beam under negative bending moment is analyzed by theoretical analysis and numerical simulation from different levels of structure and components,and the optimal calculation method and beam optimization suggestions are proposed,in order to be applied to the negative bending moment region of long-span composite beam.The theoretical analysis model is established by ABAQUS,and the extended parameter research is carried out on the basis of verifying the accuracy of the model,and the beam type is further optimized.The main results of this paper are as follows:(1)Through compression tests of UHPC materials,the effects of steel fiber content and curing time on the compressive properties of UHPC were studied.The results showed that with the increase of steel fiber content,the compressive strength of UHPC continued to increase.After 7 days of standard curing at room temperature,the compressive strength of UHPC can reach more than 80% of the standard curing specimen.Based on the comparison of existing literature and specifications,a suggested formula for the compressive constitutive equation of UHPC materials is proposed.The tensile properties of UHPC materials with different steel fiber content were indirectly obtained through splitting and bending tensile tests.(2)The negative moment loading tests of 8 UHPC narrow steel box composite beams and 1 ordinary concrete narrow steel box composite beam were completed,and the effects of parameters such as reinforcement ratio,steel box filled concrete height,and UHPC steel fiber content on the bending performance of the test beam were emphatically studied.The experimental study found that the steel fiber content has a small impact on the overall optimization performance of composite beams.Compared to the specimens with a steel fiber content of 0%,the steel fiber content increases from 0 to 1% to 2% to 3%,resulting in a yield load increase of 4.6%,6.2%,9.2%,and an ultimate load increase of 2.1%,1.2%,and 3%,respectively.The effect of reinforcement ratio and the height of concrete filled in the steel box is more significant.At the same time,the crack distribution,strain,and failure mode of the test beam under negative bending moment are obtained.(3)The calculation methods for cracking load,ultimate elastic load,ultimate bearing capacity,and maximum crack width of UHPC narrow steel box composite beams are proposed.Through comparison,it is found that the calculated values obtained by the calculation method proposed in this paper are within 20% of the experimental values,and are in good agreement.(4)A finite element analysis model of UHPC narrow steel box composite beam was established.Based on verifying the accuracy of the model,further parameter expansion analysis was conducted on the model parameters.Simulation analysis was conducted using stud spacing,steel strength of the steel box,and partially filled concrete height as variables.Based on the simulation results,suggestions for design optimization of UHPC narrow steel box composite beam were given. |
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