Study On Flexural Behavior Of High Strength Steel-UHPC Composite Beams

The steel-concrete composite beam combines the steel beam and concrete slab into a whole through shear connectors.The low strength of conventional materials leads to the problems of thick concrete slab,self weight of structure and easy cracking of concrete in negative moment area,which has become the main technical bottleneck restricting the further development of composite beams.The emergence and successful application of new highperformance materials make it possible to break through the technical bottleneck of ordinary composite beams.UHPC has ultra-high strength,good ductility and excellent durability;the yield strength of high strength steel is not less than 460 MPa.Compared with ordinary steelconcrete composite beams,high strength steel-UHPC composite beams can improve the problems of bearing capacity degradation and insufficient durability caused by concrete slab cracking.The concrete slab of high strength steel-UHPC composite beam is thin,and the height of studs is stric-tly limited by UHPC slab.The small deformation capacity of short studs leads to insufficient ductility and brittle failure of composite beam.The perforated plate connectors have high shear bearing capacity and good ductility,which are more in line with the requirements of high strength steel-UHPC composite beams for the use of shear connectors than studs.At present,there are many researches on ordinary steel and conventional concrete composite beams at home and abroad,but the research on high strength steel-UHPC composite beams has not been reported,and the application of PBL in composite beam bridges is less.In view of the above problems,this paper combined with the project of National Natural Science Foundation of China "Research on interface slip behavior and bending failure mechanism of high strength steel-UHPC composite beams"（51908138）,studied the bending behavior and bending failure mechanism of high strength steel-UHPC composite beam.The main research work and results are as follows:（1）Three high strength steel-UHPC composite beams with perforated plate connectors were designed and tested under two-point symmetrical loading at mid span.The bending stiffness,bending capacity,deflection,interface slip and strain distribution of high strength steel-UHPC composite beams with shear connectors of 1.02,0.89 and 0.76 were analyzed,and the bending failure mechanism of high strength steel-UHPC composite beams was studied.The results show that the high strength steel-UHPC composite beam with the connection of the open hole plate has high bending bearing capacity and good plastic deformation capacity.The joint of the open hole plate can guarantee the collaborative force of the concrete plate and the steel beam,and the shear connection degree has a significant influence on the flexural performance of the high strength steel-UHPC composite beam.（2）The nonlinear finite element analysis model of high strength steel-UHPC composite beam is established by ABAQUS.The comparison test results are in good agreement with the model results.The influence of the strength of the component materials（UHPC strength,steel strength）and geometric structure（thickness of concrete plate,thickness of steel flange plate and height of steel web）on the bending resistance of high strength steel-UHPC composite beam is studied.The numerical results show that the flexural capacity of composite beams can be improved by increasing UHPC strength,while the flexural capacity of composite beams can be enhanced by increasing the steel strength,but not conducive to the ductility of composite beams;the increase of the thickness of concrete slab,the thickness of steel flange plate and the height of steel web can significantly enhance the flexural capacity of composite beams,but it has little influence on the ductility of the structure.（3）The finite element model of 25 high strength steel-UHPC composite beams with different material strength was established to study the material strength matching.It is found that under the structural dimension of the high strength steel-UHPC composite beam tested in this paper,when UHPC selects RPC100 strength grade,the steel beam can be selected with Q500 to achieve the best matching in the mechanical properties of the material.（4）The applicability of section conversion method,simplified plasticity theory and calculation method of bearing capacity of composite beams with partial shear connection degree in code for design of steel concrete composite bridges（GB 50917-2013）to bending calculation of high strength steel-UHPC composite beams is evaluated.The comparison results show that the calculated results are in good agreement with the experimental results and numerical analysis results,and the existing theoretical formulas can be used as the basis for the design of bending capacity of high strength steel-UHPC composite beams.