Shear Lag Effect Study Of Steel-UHPC Composite Beam

Based on the superior mechanical properties of UHPC and the problems faced by traditional structural forms,the UHPC team of Hunan University proposed a steel-UHPC light-weight composite bridge,which can effectively reduce the structural weight and improve the spanning ability of the bridge.It also can solve the problem of easy cracking of the bridge deck.However,with the increase of traffic volume and the development of bridge technology,the main beam section becomes wider and wider,resulting in significant shear lag effect of the bridge deck,which in turn leads to a more complicated stress state of the steel-UHPC composite beam.In this paper,a new steel-UHPC(Ultra-high performance concrete)low-ribbed composite beam is studied.The purpose of this paper is to explore the shear lag effect of UHPC low-rise slabs as a composite girder bridge deck system.And by introducing the effective distribution width of the slab,the different factors affecting the shear lag effect of the composite beam are analyzed.The main contents and conclusions of this paper are as follows:(1)Taking steel-UHPC composite T-beam as the research object,a steel-UHPC composite T-beam model capable of considering both interface slip and shear lag effect is established.Based on the energy variational principle,the analytical solution of the composite beam under different load conditions is derived,and the analytical solution is compared with the finite element results.The accuracy and applicability of the theoretical model and analytical solution are verified.(2)Taking the steel-UHPC box composite beam as the research object,the correction coefficient of the cantilever plate width,position and boundary constraint characteristics of the composite beam can be introduced.The influence of the modified cantilever plate correction coefficient on the analytical solution of the composite beam bridge deck is studied.The results show that after the correction factor is introduced,the analytical solution of the stress on the UHPC roof and the steel beam floor is in good agreement with the finite element results,with higher precision and more accurate expression of the force state of the composite beam.This verifies the accuracy and applicability of theoretical models and analytical solutions.(3)A steel-UHPC composite beam scale model was designed and fabricated,and the bending performance test was carried out to investigate the shear lag effect of the UHPC plate under the bending load of the composite beam.The test results and analytical solutions and finite element calculations were carried out.Contrast,verify the correctness of the elastic analytical solution.On this basis,the shear lag effect of the composite beam in the elastoplastic phase and the plastic phase UHPC plate is studied.(4)Based on ABAQUS nonlinear finite element software,a finite element model of steel-UHPC composite beam is established.The simulation analysis results(inelastic phase)agree well with the experimental values,which verifies the correctness of the finite element model.Therefore,the finite element software can be used to continue to analyze the shear lag effect of the inelastic stage of the composite beam.(5)By introducing the effective distribution width and effective width coefficient of the slab,the difference of shear lag effect between the low-ribbed and rectangular-plate bridge steel-UHPC composite beams is compared.It is found that the low-ribbed bridge deck system is effective under the same load conditions.The width coefficient is reduced by nearly 17% compared with the rectangular plate,which indicates that the shear lag effect of the composite beam of the low ribbed bridge deck system is more obvious.If the effective width is valued according to the existing specifications,it is not safe.According to the principle of equivalent force of the section,the low-ribbed bridge deck system is equivalent to a rectangular plate for analysis.By analyzing the different factors affecting the shear lag effect of the steel-UHPC composite beam,it is found that the shear lag effect of the composite beam of the low-rise bridge deck system is related to the wide span ratio,load type,load position and other factors.The shear stiffness of the shear connector and the value of the UHPC flange plate parameters are related.In addition,the shear stiffness also has an effect on the deflection and interface slip of the composite beam.If the load type is different,the distribution law of UHPC slab effective width coefficient along the longitudinal direction of the beam is obviously different.Pay special attention to the shear lag effect of the fulcrum section and load.The results also show that the proper reduction of the width-to-span ratio and the shear stiffness of the shear connectors can reduce the shear lag effect of the low-ribbed bridge deck system.