Bending Mechanical Properties And Model Experimental Study Of Concrete Composite Box Girder With Steel Bottom Plate And Corrugated Webs

Concrete composite box girder with steel bottom plate and corrugated webs bridge is a new type of steel-concrete composite bridge.It uses steel bottom plate instead of concrete bottom plate on the basis of traditional composite box girder with corrugated steel webs.It has the characteristics of large span capacity,industrialized manufacturing and fabricated construction.At present,it has been applied in many trunk lines such as T2 and T3 connecting lines of Zhongchuan airport in Gansu Province,It is a new type of composite bridge with broad application prospects.Due to the novel structure and short application time,the research on this kind of structure is still insufficient.Therefore,the research on concrete composite box girder with steel bottom and corrugated webs has very important theoretical significance and engineering practical value.Based on the major scientific and technological project of Gansu Province "Research and industrialization of complete set technology for the construction of new highway steel-concrete composite bridges(19ZD2GA002)",this paper systematically studies the bending static and dynamic characteristics and failure modes of this kind of composite box girder by using the methods of theoretical analysis,model test and numerical simulation.The research results not only provide theoretical support for the engineering application of concrete composite box girder with steel bottom plate and corrugated webs bridge,At the same time,it also has a certain reference value and significance for the optimal design and further improvement of this kind of bridge.The main research contents and achievements of this paper are as follows:(1)Considering the effects of corrugated steel web accordion effect,shear deformation and box girder shear lag effect,the cantilever plate,top and bottom plate of composite box girder were regarded as two independent shear lag mechanical systems,and two different maximum difference functions of shear angle were set up.Based on the energy variational method,the bending static control differential equation and natural boundary conditions of composite box girder were deduced,and the closed solutions of corresponding generalized displacement were obtained.The scale model of composite box girder with corrugated steel webs was made,and the shear lag effect of the top and bottom of the model was experimentally studied.The experimental values were compared with the theoretical results to verify the correctness of the closed solution in this paper;The influence of shear lag and accordion effect on the flexural static properties of composite box girder was analyzed;The evolution laws of shear lag effect and accordion effect of composite box girder under different boundary conditions were studied.The results show that the calculated results of the closed solution in this paper are in good agreement with the experimental values and the finite element calculation results.The stress of the steel bottom plate of the simply supported composite beam under vertical load is about 20 times that of the top plate;The stronger the boundary constraint,the more obvious the shear lag and accordion effect of composite box girder.(2)The full-scale bending static test was carried out on the scale model of one span simply supported composite box girder under symmetrical concentrated loading.The variation laws of flange strain and mid span deflection of the model girder with the external load were obtained,and the bending failure model of this kind of simply supported composite box girder was defined;Combined with ANSYS finite element software,the nonlinear analysis of the whole loading process of the test model was carried out,and the bending failure mechanism of simply supported composite box girder was studied;The calculation formula of yield load and semi empirical formula of ultimate flexural capacity of this kind of composite box girder were established;The improvement method of bending mechanical properties of simply supported composite box girder meeting the requirements of coordinated failure mode was proposed.The results show that the bending failure mode of this kind of simply supported composite box girder is that the steel bottom plate yields,then the plasticity develops continuously,the structure produces large vertical deformation,and finally the concrete top surface of the top plate collapses;The calculation formula of normal section bearing capacity of composite box girder established in this paper can provide reference for the design of this kind of bridge;In the design of this kind of structure,it is suggested to use external prestress to improve its bending mechanical properties.(3)The natural vibration characteristics of concrete composite box girder with steel bottom plate and corrugated webs were analyzed.Based on the research theory of flexural static properties of composite box girder,considering the influence of shear lag effect and moment of inertia on the total kinetic energy of composite box girder,the governing differential equation and natural boundary conditions of flexural natural vibration characteristics of composite box girder were established by using Hamilton principle and energy variational method,and the closed solution of corresponding generalized displacement was obtained.The calculation program of natural frequency of composite box girder under corresponding boundary conditions was compiled by MATLAB;The correctness of the above closed solution was verified by testing the natural frequency and vibration mode of the composite box girder;The effects of accordion effect,shear deformation and shear lag effect on the natural vibration characteristics of composite box girder were analyzed;The effects of boundary conditions,width span ratio,box girder height and steel bottom plate thickness on the natural vibration characteristics of composite box girder were obtained.The results show that the calculation results of the closed solution in this paper are in good agreement with the finite element calculation results and the model test values.It is reliable to calculate the natural vibration characteristics of steel box composite continuous beams with corrugated webs by using the converted section method;Compared with the shear lag effect,the shear deformation of corrugated steel webs has a greater impact on the vertical stiffness of composite box girder.(4)Based on the free vibration analysis theory of composite box girder,considering the influence of shear lag effect and moment of inertia on the total kinetic energy of composite box girder,the control differential equation and natural boundary conditions of bending simple harmonic forced vibration of composite box girder were established by using Hamilton principle and energy variational method,and the closed solution of corresponding generalized displacement was obtained,Combined with ANSYS finite element software,the influence of shear lag effect and shear deformation on the dynamic stress and dynamic deflection of flange plate of composite box girder was studied.The results show that the dynamic stress of the flange plate of the composite box girder considering the shear lag effect is in better agreement with the finite element numerical solution.Under the action of simple harmonic concentrated force,the distribution characteristics of the dynamic stress amplitude of each point on the cross section of the composite box girder are similar to its static analysis results,and the influence of the shear lag effect on the dynamic stress amplitude of the flange plate of the composite box girder increases with the increase of the width span ratio.