Influence Line-based Bridge Damage Assessment:Mechanism Analysis And Sensitivity Analysis

In the past few decades,Bridge construction has entered a golden age of rapid development in China.After the massive construction,the attendant problem is operation management of existing bridges that the key is to insure the security of these bridges in long-term operation service period.During normal operations of the bridge,Regular detection of bridge damage will benefit early diagnosis of structural disease,which will reduce the rate of disastrous accident and has important practical significance and theoretical value.After years of research,a number of different damage assessment method based on various structural performance indices for bridges has been proposed by scholars at home and abroad.Among these indices,the influence line(IL),one of the intrinsic properties of the bridge,is well suited to be developed into a key index for the damage assessment because of its clear physical significance,sensitivity to damages and insensitivity to environmental change.But so far there are still many crucial issues need to be solved urgently of applying ILs to the detection of bridge damages.In this paper,the mechanism and sensitivity analysis of the bridge damage detection based on ILs are taken are studied,and the research is carried out in detail.The existing research on the mechanism of ILs applied to bridge damage detection is mostly based on the elasticity analysis model,so the disadvantage is that it cannot truly reflect the change of ILs during the processing of bridge failure,and cannot analyze the variation of ILs under different detection loads.This paper takes reinforce concrete(RC)beam bridge as the analysis object,and the mechanism of the bridge damage assessment is studied based on the variation law of the IL.By comparing and analyzing several kinds of classical finite element(FEM)models of RC Beam Bridge,the numerical model suitable for the study of the IL was selected.By simulating the local application of the destructive load and gradually increasing the load,the change law of the IL in the process of the destruction was studied;considering the structure of non-destructive state and varying degrees of damage state,the variation law of ILs under different detection loads was studied,and the detection-load interval for stable identification of ILs was obtained.This paper found that with the occurrence of local damages and the increasing of damage degree,the deflection influence line(DIL)and strain influence line(SIL)have changed regularly,indicating that IL-based indices are promising to develop into a key index of bridge damage assessment.In addition,by studying the detection-load range of stable identification of ILs,it is proved that the IL-based indices for damage detection are feasible in real bridge application.The sensitivity of IL-based indices to the damage will be affected by various factors,such as the different sensor type or the location of measuring points will cause differences,and noise interference will also affect the sensitivity.This paper deduced the mathematical expressions of the sensitivity coefficients of various types of IL-based indices;based in the numerical examples,the sensitivity of the multi-type IL-based indices to the stiffness damage was analyzed;through the normalized IL indices,the damage sensitivity of different types of IL-based indices was compared;by considering the influence of noise disturbance on the damage sensitivity of the IL index,the effective detection range of the IL index after adding noise was analyzed;also considering that the damage location is usually unknown,the comprehensive analysis ability of different IL indices for unknown damage was studied.Through above research,it was found that the degree of sensitivity of the IL indices has a tendency to decrease with its measuring point location away from the damage location,and the decay rate of the SIL index is faster than the DIL line,and there were a series of other conclusions like this.Finally,this study produced a three-span continuous RC beam model in the laboratory,using the load car moving on the beam to simulate the loading process of the IL,by applying destructive at the central of the mid span to simulate local minor injuries,obtaining DILs and SILs of different measuring points before and after damage,and through the analysis of the test results,the mechanism and sensitivity of IL indices applied to assess the bridge damage were verified.