Research On Damage Identification Of Variable Cross-section Beam Based On Deflection Influence Line

With the rapid development of traffic construction,more and more bridges have been constructed, and then the bridge safety conditions under the normal operation status have attracted more attention. The variable cross-section beam has more reasonable force than the constant section beam, and it is widely used in continuous girder bridge and continuous rigid frame bridge of medium and small span bridge, and the safety conditions of bridge should be paid more attention. Bridge health monitoring can preferable provide bridge information every moment, grasp the overall state of bridge health conditions as well as discover early damage of local region and repair the damage timely. As the core of bridge health monitoring system, damage detection has already received extensive attention of the researchers both at home and abroad. Deflection influence line has the advantages of high measuring accuracy,good stability, less measuring point and so on. So using deflection influence line to construct indexes to identify the bridge damage has certain research significance..Based on current research status of damage identification, the damage identification of variable cross-section beam based on the deflection influence line has been studied in this paper. It is verified through theory, numerical simulation and model experiment verification that the indexes based on deflection influence line can identify the damage of variable cross-section beam, and this way of identification has good effect. The main work of this paper is summarized as following:It has been generalized the development and significance of bridge health monitoring system, reviewed the common methods of damage identification, analyzed the advantages and disadvantages of common methods of damage identification, and introduced the situation of application of variable cross-section girder bridge and the damage identification methods based on deflection influence line in this paper.According to the principle of virtual work, the analytic solutions of the deflection influence line of simple support beam that stiffness is lineal changed along the beam has been deducted. Deflection influence line has been formed four damage detection indexes,respectively, the deflection difference influence line, the first derivative of deflection difference influence line, the second derivative deflection difference influence line and the second derivative deflection influence line. And the varying patterns of the four indexes under intact and damage structural have been analyzed. Theoretically, four indexes have the ability to detect the damage of variable cross-section beam. In the case of no original data, structural damage can be detected by the second derivative of deflection influence line; or it can be preferable detected by deflection difference influence line as well. When used deflection influence line to detect microlesion, the effect of identification result may be not good enough.It can be helped to use wavelet transform to detect damages, then it can be proved that the effective of detected microlesion is preferable.Numerical simulation of simple support and continuous of variable cross-section beam has been taken in this paper, it has been applied deflection influence line to form different indexes to detect damage, and analyzed the sensitivity of the identification effect of the indexes which based on the deflection influence line. The results reveal that four indexes can preferable detect structural damage, no matter it is a single damage or multi-damage. As for the identification effect, the deflection difference influence line is better than the second derivative of deflection influence lineThree-span variable cross-section beam model is built in the laboratory, and the deflection influence line in the middle-span of the beam is obtained with new high-precision digital measuring equipment. Accordingly, the deflection difference influence line is used to detect the model’s damage, and the research result shows that deflection difference influence line can detect the damage of the variable cross-section beam effectively.From the results of theory, numerical simulation and model experiment, it can be concluded that the damage identification method which based on deflection influence line is simple, effective, stable and feasible when identifying the damage of the variable cross-section beam, also, it has accurate data and less measuring point.