Damage Detection In Bridge Structures Using Influence Lines

The bridge structure plays a vital role as a key hub in transportation.Its normal operation is closely related to personal safety,national property and social stability.However,due to internal(material aging)or external factors(earthquakes,etc.)the impact of the bridge will cause different degrees of damage,timely detection of damage and damage to the site for the maintenance of treatment has important practical significance and social value.In this paper,the damage identification method based on the influence lines of the deflection difference and the influence lines of the strain difference before and after the damage is proposed.The concrete contents are as follows:(1)The theoretical formulas of the influence lines of the difference(difference,first order and second order)on the three-span continuous beam bridge under symmetrical load and symmetrical measuring point are deduced,and the Damage identification method of deflection difference under symmetrical load and symmetrical measuring pointthe is explained from the theoretical level.(2)Taking the three-span continuous girder bridge,the three-span variable-section continuous girder bridge,the variable-section box-type track beam and the T-beam as the model,the influence lines of the deflection difference under the symmetrical load and the symmetrical measuring point is used to detect damage.Thedeflection difference classinfluence lines of different bridge types under the action of the symmetry load and the symmetry measuring point is compared.Which shows the advantages and disadvantages of symmetrical load and symmetrical measuring point method in different bridge damage recognition.(3)Aiming at the structural damage detection based on the static test data,a method of damage recognition based on the strain difference influence lines is developed.Considering that strain is more sensitive to local damage.The strain influence lines on the pre-defined strain measurement elements of the bridge component under the unit moving load is utilized to carry out the difference and derivation calculation,thus the damage diagnosis method based on strain difference,first order and second order influence lines as damage index is put forward,The effect of the index on the identification of the diagonal bar or the vertical bar is studied,and the identification effect on the different rods is analyzed.(4)Damage recognition based on the difference influence lines can quickly locate and qualify the degree of damage,but can not identify the specific damage degree.The conjugate gradient method(CG)method transforms the damage identification problem into solving the optimization problem of the objective function accurately,which is different from the influence lines method.The damage degree can be accurately identified and the convergence speed is fast.Therefore,the CG method is used to identify the damage.For the large span bridge structure,based on the rapid detection of the damage area by the difference class influence lines.TheCG method is applied to the cantilever beam and T-beam respectively,which proves the convergence of the CG method and the validity of the damage degree in the damage degree.(5)Based on the influence lines of the strain difference class,the damage of the truss structure is studied,and the influence of the different moving load path on the damage recognition effect is studied.It is proved that the strain difference Method for Rapid Detection of Damage on Large Span Complex Bridge.