Study On Bending Properties Of Composite Thin-walled Box Beams With Variable Thickness

Glass fiber reinforced composites have good application prospects in emergency rescue bridges because of their excellent properties,such as light weight,high strength,good designability,strong heat resistance,good corrosion resistance and so on.In this paper,the equal thickness web of box section in emergency bridge is changed into variable thickness web,which can further reduce the weight of the structure on the one hand and greatly improve the utilization rate of materials on the other hand.Due to the change of the thickness of the box girder web,the bending stiffness of the box girder section changes,which makes the bearing capacity of the structure,especially the bending performance,is quite different from that of the box girder with equal thickness.At the same time,when the wheel load acts on the composite thin-walled box beam,the concentration effect is more obvious,which is prone to local buckling failure.Therefore,on the basis of considering the effect of variable thickness on the bending properties of composite thin-walled box girders,this paper makes an in-depth study on the bearing mechanism and calculation method of variable thickness composite thin-walled box girders by means of model test,finite element numerical simulation and theoretical analysis.The main work and conclusions are as follows:Based on the elementary beam theory,the overall bending stiffness of composite thin-walled box girders with variable thickness is analyzed,and a method for calculating the deflection of thin-walled box girders considering the effect of shear stiffness is put forward.by using the equivalent principle,the variable thickness web is equivalent to the equal thickness web,and the formula for calculating the critical buckling load of the web and wing plate of the variable thickness composite thin-walled box beam considering rotational constraint stiffness is derived.The influence of the thickness and width of web intermediate plate on the critical buckling load of composite thin-walled box girder with variable thickness is analyzed.The bending tests of three composite thin-walled box beams with variable thickness were carried out,and the results of failure mode,load-displacement curve,bending strain and flange strain of the beam were analyzed.From the test results,it can be found that the larger the distance between the pure bending segments,the greater the bearing capacity and displacement of the composite thin-walled box beam with variable thickness.When the pure bending distance is 1000 mm and 900 mm,the web appears transverse crack and out-of-plane buckling at the loading position,and finally the shear failure and upper flange collapse failure are caused by the local buckling of the web.When the pure bending distance is 800 mm,the web of the composite thin-walled box beam with variable thickness appears oblique crack at the loading position and runs down to the edge of the lower flange plate,and the out-of-plane buckling occurs at the same time.Finally,the local buckling of the web leads to shear failure and upper flange collapse failure.The finite element analysis software is used to analyze the linear and nonlinear buckling of three composite thin-walled box beams with variable thickness.Through the comparison between the test results and the nonlinear buckling simulation results,the correctness of the finite element simulation is determined.Under this premise,the effects of upper flange thickness and inner chamfer radius on the buckling bearing capacity and failure mode of composite box beams with variable thickness are studied respectively.