Distortion Effect Of Concrete Composite Box Girder With Steel Truss Webs

Concrete composite box girder with steel truss webs is a new type of box girder,which uses the shear connection structure to connect the steel truss web and the concrete roof and floor as a whole and work together.It has the advantages of beautiful shape,good ventilation performance,high structural efficiency and short construction period,which accords with the development trend of modern urban bridge construction.After the steel truss web is used to replace the traditional concrete solid web in the box girder,the stiffness decreases,resulting in that the warping normal stress of this kind of box girder is greater than that of the ordinary concrete box girder under the eccentric load.therefore,the distortion effect of this kind of composite box girder under eccentric load has become a problem that must be considered.In this paper,the distortion effect of steel truss web-concrete composite box girder is studied deeply by the combination of theoretical analysis and finite element numerical simulation.The main contents and conclusions of this paper are as follows:(1)Based on the structural and mechanical characteristics of steel truss web-concrete composite box girder,considering the contribution of concrete area at both ends of steel truss web to the longitudinal stiffness of composite box girder,the concept of concrete common working area is put forward.in this paper,the distribution mode of distorted principal sector coordinates suitable for this kind of composite box girder is redefined,and the calculation method of distorted warping moment of inertia considering the common working area is given.(2)Based on the thin-walled box girder theory,the distortion calculation theory which is unified with the constrained torsion is introduced to simplify the analysis and solution process of the composite box girder under the antisymmetric load.The distortion angle suitable for concrete composite box girder with steel truss webs is defined through the distortion center.On the basis of the new generalized sector coordinates distribution model,the distortion control differential equation is established by using the energy variational method based on the stationary principle of potential energy.The initial parameter solution including Krylov function is given.Through a numerical example,it is proved that the basic assumption used in the distortion analysis of steel truss web-concrete composite box girder accords with its stress characteristics.(3)According to the mechanical characteristics of steel truss web-concrete composite box girder,the distortion control differential equation is established by the improved plate element analytic method,and the analytical solution of distortion effect is given according to the actual engineering boundary conditions.through a numerical example in the form of rectangular section,the influence of steel truss web instead of concrete solid web on the distortion stiffness and distortion stress of composite box girder is studied.The results show that compared with the traditional concrete box girder with solid web,due to the use of open web,the distorted warping normal stress of steel truss web-concrete composite box girder is about 1.71 times that of concrete box girder,and the numerical example of composite box girder with trapezoidal section shows that the distortion analysis theory of steel truss web-concrete composite box girder established by plate element analytic method also has better calculation accuracy for trapezoidal cross-section composite box girder.(4)The distortion characteristic parameters of steel truss web-concrete composite box girder are analyzed by using the distortion theory established in this paper.The results show that the distance between the distortion center and the roof increases with the increase of width-span ratio,the transverse distortion frame stiffness decreases with the increase of beam height,and the distortion double moment and distortion moment first decrease and then increase with the increase of internode distance.on the premise of not increasing the self-weight of the composite box girder,increasing the thickness and diameter of the steel truss web will enhance the transverse distortion frame stiffness of the box girder and reduce the distortion internal force.With the increase of beam width,the distorted double torque increases significantly,the distribution trend of bimodal in the longitudinal direction is gradually smooth,and the position of producing the maximum double torque moves to the middle of the span;with the increase of the pitch angle of the web,the distorted double torque of concrete composite box girder with steel truss webs gradually decreases,and the position that produces the maximum double torque moves to the fulcrum.