Research On Damage Identification Of Steel-Concrete Composite Girder Bridge

Steel-concrete composite beams connect steel beams and concrete slabs together through shear connectors,so they have the advantages of two different materials :steel(tensile)and concrete(compressive).With the increasingly widespread application of steel-concrete composite girder bridges,there are also some corresponding problems.Steel beams,shear connectors and concrete are prone to corrosion or cracks under the influence of load,environmental impact,lack of normal maintenance and natural disasters,which reduces the overall performance and bearing capacity of the structure,and even causes damage to the structure.Collapse.Based on the Open Fund of Hebei Key Laboratory of Structural Health Diagnosis and Control(KLLSHMC2112)’ Research on damage identification and residual bearing capacity of multi-girder assembled composite girder bridge ’,combined with the characteristics of steel-concrete composite girder,this thesis studies the damage identification of steel-concrete composite girder bridge based on modal parameters and long gauge strain influence line theory through theory and experiment.The main work and conclusions are as follows :(1)The finite element model of steel-concrete composite beam is established.The modal curvature method and modal curvature difference method are used to identify the single-point and multi-point damage of steel beams and studs,and the effectiveness of the identification method is verified by experiments.The results show that the single-point and multi-point damage of the stud can be identified by the modal curvature method by selecting the appropriate path and measuring point spacing.According to the modal curvature difference before and after the damage,the recognition effect is more intuitive.The test results can identify the damage of composite beams,but the recognition effect is greatly affected by the test accuracy.(2)The real bridge model of multi-beam composite girder bridge is established.According to the longitudinal and transverse modal curvature,the longitudinal and transverse modal curvature difference before and after damage is obtained,which is used as the damage index to identify the damage of steel beam,wet joint and stud.The results show that the damage identification method based on single-order modal curvature difference is better when the structure is damaged at a single point.When the structure is damaged at multiple points,the sudden change value of modal curvature difference is different,which is easy to cause misjudgment.The damage identification method based on the change rate of superimposed modal curvature difference is effective for single-point and multi-point damage identification.(3)The damage identification method based on distributed long-gauge strain influence envelope under moving load is studied.The expression of long-gauge strain influence line under moving load is derived.The strain influence envelope difference index is obtained by subtracting the strain influence envelope before and after damage to identify the damage location of the structure.The results show that according to the finite element simulation analysis,the load parameters have a certain influence on the strain influence envelope method.The long gauge strain influence envelope is suitable for the damage identification of composite girder bridges,and the damage location can be accurately identified.