Damage Identification Of Simple Supported Bridge Based On Sensitivity Method

Not only a lot of investment is required in the civil engineering,but also the service time should last hundreds of years because of itsimportant influence to now and tomorrow of our country. So is the bridgestructure. With the increase of traffic and prolong of the service timeof the bridge structure, the appearances that the decrease in theperformance, aging and damage happen in quite a lot of the bridgestructure. Therefore, requirements can't be satisfied. If the damageis not properly inspected and detected, it is possible to lead to thecasualty and collapse of the bridge. Even the accident can bring greatloss in economic. And that, for the bridge structure, replacing themember and rebuilding will influent the normal traffic. So moreattention should be paid to the damage diagnosis of the existing bridge,reliability evaluation, maintenance and strengthening technique forthe engineers and technicians. Further study is required to improve theresisting capacity and extend the service time for the existing bridgein purpose to save the building fund.Traditional damage detection method mainly includes the appearancedetection, the non-destructive detection, minor destructive detectionand load test in field and the sample destructive detection in specialcircus and so on. Generally, the traditional detection methods can'tacquire comprehensive information especially for the not bare parts.Moreover, the extent in precision of the detect result depends on theexperience and subjective estimation of the detectors. Therefore, itis difficult to systemically evaluate the safety and path of degradation.However, the damage identification method based on the structuraldynamic characteristic is the evaluation method for the whole structure.And this method can identify the damage well.The damage identification methods based on the structural dynamiccharacteristic usually include: the method based on FRF waveform;themethod based on inherent frequencies;the method based on the vibrationshapes;the method based on the strain modes and strain energy;themethod based on the neural networks and the method based on thesensitivity and so on.Commonly, the structural identification method based on thesensitivity adopts partial derivative to acquire sensitivity matrix ofstructural modal parameters with respect to structural physicalparameters (stiffness, damping, the moment of inertia etc.). In mostcases, the relation between modal parameters and physical parametersis not obvious. So it is not convenient to obtain sensitivity using thismethod. Therefore, based on perturbation theory, a method with whichwe can acquire sensitivity matrix of structural modal parameters forstructural physical parameters is presented in this paper. This methodis more convenient during the formation of structural sensitivitymatrix without the calculation of partial differential. In order toachieve high precision of structural damage identification in thecondition that few modes are referred to during the formation ofstructural sensitivity matrix, Guyan reduced method is adopted toreduce the structural freedoms. At the same time, the standard errorof physical parameters of simple supported bridge is analyzed in thepaper using random perturbation theory and probability theory in thecondition that 1% random error is introduced in the first two vibrationshapes of undamaged and damaged simple supported bridge.Finally using the free vibration shapes of undamaged and damagedsimple supported bridge acquired from the free vibration analysis withfinite element method as the basis, we carry out numerical simulationof damage identification of simple supported bridge. The results showthat the method presented in this paper is effective, convenient andreliable.