Mechanical Performance Of Steel-concrete Composite Beam Bridge Under Overloaded Vehicles

With the increasing application of steel-concrete composite structures in bridge engineering,the fatigue problems faced by steel-concrete composite beam bridges have become increasingly prominent,especially it is not uncommon for fatigue damage or even destruction of bridge structures due to overloaded vehicles and safety accidents.This thesis takes the steel-concrete composite beam bridge as the research object,and conducts research on its mechanical performance under the action of overloaded vehicles through theoretical analysis and finite element analysis methods.The main research work is as follows:(1)Based on the definition of fatigue,combined with different standards fatigue problems are classified,and three methods for steel-concrete composite beam bridge fatigue analysis are given: material mechanics method,damage mechanics method and fracture mechanics method,which provides a theoretical basis for subsequent research.(2)The improved reduced stiffness method is introduced into the calculation of fatigue deformation of composite beams,and the calculation formula of fatigue stiffness of composite beams is obtained based on the quantitative relationship between structural deformation and stiffness;combined with the stiffness degradation function,the fatigue stiffness degradation law of the test beam is analyzed;The influence law of overload on the fatigue stiffness degradation is studied.The results show that the fatigue deformation calculation method of the improved composite beam has a lower dispersion and a wider application range;the fatigue stiffness of the composite beam is degraded in an "S" shape with loading,and the degradation rate and amount of fatigue stiffness in the initial and final stages are significantly higher than in the mid-loading period;overloading will increase the rate and amount of degradation in fatigue stiffness of composite beams,and even change the degradation law from a slow "S" shape degradation to a sharp one in a short period of time.(3)The calculation formulas for the residual bearing capacity of composite beams under different shear connection degrees are deduced,the finite element calculation method of the residual bearing capacity of composite beams is studied,and the law of the influence of overload on the residual bearing capacity of composite beams is analyzed.The results show that the results calculated based on the finite element analysis method are in good agreement with the test results;overloading will change the degradation law of the remaining bearing capacity of the steel-concrete composite beam,which has a particularly significant impact on the end of loading;at the same time,overload will accelerate the degradation rate of the remaining bearing capacity of the steel-concrete composite beam and increase its degradation.(4)Taking a steel-concrete composite girder bridge as a calculation example,the load amplitude of the bridge is calculated based on the correction coefficient of the influence of overloaded vehicles,and the fatigue stiffness and residual bearing capacity of the composite beam bridge under different overloading degrees are analyzed with operating time.The law of change.The results show that the fatigue stiffness and residual bearing capacity of the composite beam bridge show an irreversible degradation trend under different overloading degrees;the increase of the overloading degree will make the fatigue stiffness of the composite beam bridge degenerate from "S" shape to parabolic shape,but the influence of the degradation law of the residual bearing capacity is not obvious.At the same time,the degradation rate of the fatigue stiffness and the residual bearing capacity of the steel-concrete composite beam accelerates and the amount of degradation increases.