Experimental And Theoretical Study On Bearing Capacity Of Steel-concrete Composite Beams

The steel-concrete composite beam has the mechanical advantages of both concrete and steel,its mechanical performance is excellent,it is competitive in small and medium span bridges,and has remarkable technical and economic benefits.In recent years,the construction of steel-mixed composite girder bridge has been greatly developed due to the promotion of iron and steel de-capacity policy in our country,and its application prospect is very wide.However,the relevant theoretical and experimental studies are not perfect,and the relevant design codes are conservative in bearing capacity design.On the basis of experimental study on bending and shear properties of composite beams,the calculation methods of bending and shear strength of composite beams are adjusted and optimized in this paper.The main contents are as follows:(1)the bending and shear tests of 8 simply supported steel-concrete composite beams are completed.The deformation,strain and load data of the test beams during the whole process of loading and failure are obtained,and the ultimate loads are compared and analyzed.The results show that when the bending shear is large,the flexural failure of the composite beam will occur and the flexural bearing capacity will not be affected by the shear force.With the decrease of bending-shear ratio,the failure mode of composite beam is gradually transformed into shear failure,and the flexural bearing capacity of composite beam is reduced to a greater extent.(2)Based on the continuous strength method and bilinear strengthening material model of steel beam,the elastoplastic analysis of composite beam section is carried out,and the calculation mode of flexural bearing capacity considering strain strengthening effect of steel beam is obtained.On this basis,the corresponding numerical program is compiled,and the analytical results are in good agreement with the experimental results.(3)Taking the relative height of plastic neutral axis(Dp/h)as the main parameter,the ultimate bending strength of a large number of composite beams is numerically analyzed,and a simplified formula based on plastic theory is established.The results are compared with those of European Code 4 and American AASHTO Code.The results show that the calculation results are conservative and the calculation accuracy of the simplified formula in this paper is higher than that of European Code 4 and American Code 4.In addition,taking the strain strengthening level of steel beam and the contribution degree of bending bearing capacity as the criterion,the calculation formula for quantitatively evaluating the strain strengthening degree of steel beam is determined.(4)The finite element model of the test beam is established by using the general software ABAQUS.On the basis of the effective verification with the test results,the bending shear ratio and flange plate thickness affecting the bending and shear behavior of the composite beam are studied.The factors such as the ratio of height to thickness of steel beam and strain strengthening effect of steel beam are analyzed.Combined with the relevant test data and finite element calculation results,the calculation formula of shear strength and the evaluation standard of bearing capacity under the action of bending-shear combination are obtained by fitting the data.The calculation of shear resistance formula is simple,which is in good agreement with the experimental results,and can be used as a reference for engineering design.The bearing capacity evaluation criteria can effectively determine the characteristics of bearing capacity of composite beams under the action of bending-shear combination.The results take into account the requirements of safety and are of high applicability to engineering design.