Research On Damage Identification Method For Hanger Of Tied Arch Bridge Based On Beam Deflection

As an essential force transmitting member of the through-tied arch bridge,the hanger(cable)often suffers from corrosion,anchorage failure,steel wire breakage,and other damages due to the influence of various factors such as environmental erosion and vehicle loading during the bridge operation.Damage to the hanger will directly cause changes in the stress state and line type of the bridge structure and,in severe cases,even threaten the operational safety of the bridge structure.Studying the damage identification of the hanger,identifying the location and damage degree of the damaged hanger in time,and carrying out effective maintenance or replacement is of great significance to improve the structure’s service state and prolong the bridge’s service life.It is of great theoretical significance and practical value to ensure the operation safety of through-tied arch bridges.Regarding the tied-arch bridge,the hanger damage will inevitably lead to a change in beam deflection under the determined external load.In this thesis,the hanger damage identification method of a through-tied arch bridge is studied based on the change of beam deflection.The main research contents and conclusions are as follows:(1)The feasibility of hanger damage identification based on beam deflection was analyzed.Based on an actual through-tied arch bridge,the benchmark finite element model was established,and the influence of hanger damage on the deflection of the beam was analyzed.The variation law of beam deflection difference before and after different degrees of damage of hangers in different positions was simulated through numerical calculation.The variation law of beam deflection difference before and after hanger damage was analyzed when considering the influence of temperature change,bridge overall stiffness degradation,concentrated load,and other factors.The results show that the deflection difference of the beam is sensitive to the damage of the hanger,and the distribution of deflection difference caused by hanger damage is obvious.For example,before and after the damage of a single hanger,the deflection difference distribution curve of the side beam where the damaged hanger is located shows the characteristic of a single peak,the peak value is proportional to the damage degree of the hanger,and the peak position corresponds to the position of the damaged hanger.The deflection difference of the beam near the anchorage point(peak position)of the damaged hanger is significant,while the deflection difference of the beam far from the anchorage point of the damaged hanger is almost zero.(2)The location identification method of damaged hanger was studied by using the third-order difference of beam deflection.The relationship between the change of cable force and the difference in beam deflection was derived,and a position identification index DI(i)of the damaged hanger based on the third-order difference in beam deflection difference was proposed.The location of the damaged hanger can be accurately identified according to the distribution law of DI(i).The recognition method was verified by numerical simulation and model experiments.The results show that no matter whether the single hanger is damaged alone or two hangers are damaged simultaneously,no matter what the damage degree is,the location of the damaged hanger can be accurately identified by using this identification index.(3)The location identification method of damaged hanger was studied by using the influence matrix of beam deflection difference.The distribution law of the deflection difference of the beam before and after the complete damage of each hanger was studied,and the deflection difference series vectors of the anchorage points corresponding to the complete damage of each hanger were arranged to form the deflection difference influence matrix.The deflection difference influence matrix and the contribution rate to the deflection difference of each damaged hanger to any anchorage point can linearly express the deflection difference of a hanger before and after damage.As a result,another position identification index {η} of the damaged hanger based on the influence matrix of beam deflection difference was proposed.The value of this index is the highest at the anchorage point of the damaged hanger and the beam and very small at the anchorage point of other hangers.The results of numerical simulation and model experiments show that the location of the damaged hanger can be accurately identified by using the identification index,whether a single hanger is damaged alone or two hangers are damaged simultaneously,regardless of the degree of damage.(4)The identification method of hanger damage degree was studied based on neural network and local vehicle loading respectively.After identifying the location of the damaged hanger,the column vector formed by the abrupt variable(value)of the identification index DI(i)(or{η})at the anchorage point of each hanger and beam was used as the input of the network;the location number of the damaged hanger and the damage degree of the hanger were used as the output to train the RBF(Radical Basis Function)neural network.The trained RBF neural network can be used to identify the damage degree of the hanger quantitatively.In addition,after the location of the damaged hanger was determined,a method to directly identify the damage degree of the hanger by applying a concentrated load was proposed.The specific calculation formula of damage degree was given through theoretical derivation.(5)The damage identification method in hanger of arch bridge was studied by using arch bridge model.An experimental model of a through-tied arch bridge was designed and made.The model can accurately simulate all kinds of hanger damage(different hangers at different positions occurred different degrees of damage).The effectiveness of the damage hanger location identification and damage degree identification methods proposed in this thesis was verified through simulation experiments.(6)The applicability of the method of hanger damage identification was studied.This thesis mainly analyzes the influence of temperature change,different beamarch stiffness ratios,bridge overall stiffness degradation,concentrated load,and measurement noise on the identification effect of the two position identification methods of damaged hangers proposed in this thesis.The results show that the influence of temperature change on the deflection difference of the beam can be eliminated by numerical calculation;the degradation of the overall stiffness of the bridge and the application of concentrated force(or vehicle load)near the anchorage point of each hanger are helpful to improve the measurement accuracy of beam deflection difference;the two identification methods are robust to the noise of deflection measurement.