Effects Of Prestress On The Mechanical Properties Of Box Girder With Corrugated Steel Webs

With the extensive application of prestressed concrete box girder with corrugated steel webs in China,a lot of research has been done on its mechanical properties under different stress states by scholars.According to the theoretical analysis,finite element analysis and model test,the structural performance of prestressed concrete box girder with corrugated steel webs is understood.When scholars study the mechanical properties of prestressed concrete box girder with corrugated steel webs,most external loads are concentrated and uniformly distributed.While,the main method of research on the overall mechanical characteristics and shear lag effect of box girder in prestress is equivalent load method.In this paper,the model test beam of prestressed concrete box girder with corrugated steel webs is studied.On the basis of domestic and foreign research results,according to model test and ANSYS finite element analysis,the mechanical properties of concrete box girder with corrugated steel webs in prestress are studied systematically.The theoretical analysis and calculation method of the bridge structure is derived.The main work of the thesis is as follows.The model test of the concrete box girder with corrugated steel webs which was focred by prestressing was carried out.The mechanical properties of the beam in prestress were tested.According to the comparison and analysis of the model beam test results and finite element calculation results,the mechanical properties of the bridge structure in prestress were revealed.Roof and floor stress distribution state of cross section was compared.The stress distribution law of the key section of the structure was obtained.The cross-section and 1/4 cross-section deflection distributions were compared.The deflection distribution law of the key section was obtained.The research results provide the reference for engineering application.It is assumed that hysteresis function of the box girder shear is cubic paraboloid function.According to the principle of minimum potential energy,the shear lag control differential equation of corrugated steel web box girder in prestressing force is deduced by energy variation method.According to the stress boundary conditions,the analytical expressions of equations with different prestressed beam lines are given.According to the model test beam,ANSYS finite element model is established.Based on numerical analysis,analytical solution and model test,the shear lag coefficient distribution of the concrete box girder with corrugated steel webs is analyzed.The stress distribution of steel webs is also studied.The differential equation of shear lag is deduced by energy variational method,and displacement control differential equation is substituted.The shear lag equation is substituted into displacement control differential equation.The displacement equation is obtained by the integral method.According to the displacement boundary condition,the analytical expressions of the displacement of the beam with different prestressed beams are given.Based on numerical analysis,analytical solution and model test,the deflection distribution of concrete box girder with corrugated steel webs is analyzed.The influence of shear deformation of steel webs on deflection is studied.Box girder with corrugated steel webs will deform under external load.The deformation of the beam forces the prestressed tendons to deform together.This is equivalent to the prestressed tendons are applied a force by the beam in the same direction with the deformation of the beam.According to the action and reaction,the prestressed tendons apply a force which is opposited to the deformation of the beam.This is equivalent to adding an additional bending moment.Taking the simply supported box girder with corrugated steel webs under uniform load as an example,the shear lag control differential equation considering the influence of prestress is derived by using the energy variational method.This equation is a fourth-order linear differential equation with constant coefficients.It is substituted into the displacement control differential equation,and according to the displacement boundary condition,the displacement solution expression considering the influence of prestress is given.The influence of prestress on the model beam is compared and analyzed.The concept which is work tension of prestressed reinforcement is given.The length of the prestressed reinforcement changes with its vibration and the working tension changes with the length of prestressed reinforcement changing.Based on energy variation principle and Hamilton?s principle,Vertical vibration differential equation of simply supported beam which is applied by prestressing force is derived.Analytical solution formula which is about influence of prestressing force on frequency is achieved.In theory,analytical solution shows that simply supported beam with prestressed can improve the natural frequency of vibration.The vertical vibration differential equation of simply supported composite box girder with corrugated steel webs which is prestressed is given based on the Hamilton principle and energy variational method.In this paper,the analytical solution formula which is about the influence of shear lag and prestress force loaded on the simply supported beam is given.The analysis of analytical solution formula proves that the prestress force can improve the vertical natural frequency of vibration of simply supported composite box girder with corrugated steel webs.The self-vibration frequency of the model test beam in different prestress is tested and analyzed theoretically.The results show that the prestress can improve the vibration frequency of the test beam.But the measured frequency increases more than the theoretical analysis.There are some factors that are not considered in theoretical analysis.The impact of these factors should be studied in the future work.