Research On The Key Problem Of Damage Identification Method For Half Through Or Through Concrete Filled Steel Tubular Arch Bridge

Half through or through concrete filled steel tubular arch bridge (CFSTAB) is a newly-developing type bridge and widely applied. But in recent years there are many collapse accidents of half through or through CFSTAB both at home and abroad which have caused great casualties and economic losses. According to the statistics, the main cause of the accidents is anchorage failure or hanger corrosion fracture. Because the disasters are closely related to the health statu of the bridge, most of accidents could be avoided if the extent of damage and health status of the bridge can be assessed in time. The damage of this type bridge mostly occurred in beams, tie bars, suspenders and other components. So such damage detection is the key problem of damage identification for half through or through CFSTAB.In this paper, the crucial problems to solve in damage identification method for half through or through CFSTAB have been studied and some corresponding solutions have been put forward. Main research results of the thesis are as follows:1) For beams, tie bars damage identification a new method based on the perturbations of frequencies and mode shapes is proposed. First, according to the changes of mode shapes between damage and undamaged structure, damage pre-determination and determination equations are established. The perturbation of mode shapes are used to solve element damage parameters, then the detection results are substituted into damage check equations based on frequencies differences to check the precision of the results. The damage detection equations established from this method can guarantee the uniqueness of recognition results, avoid "pseudo damage" phenomenon. Numerical examples and the tests show that even the structure are multiple and low extent damaged, only one-order mode is need to identify the damage.2) For large-scale structure and the incomplete test information a concept of generalized residual force vector and a new method for structure damage detection based on generalized residual force vector are advanced. Firstly, the damage structure is measured to get the residual force vector matrix. Then the matrix is compared with the one of undamaged structure to get the difference matrix. The biggest absolute value in each row of the difference matrix formed the generalized residual force vector. In damage identification the improved residual force vector is defined to locate the suspected damaged elements preliminarily. Then the damaged extent is estimated by frequency perturbations. The numerical simulation and experiments prove the feasibility of the method.3) The influence has been analyzed to suspender tension and deck displacement caused by the damage in suspender based on the perturbation theory. And a new method of damage identification for suspender is advanced based on the change of suspender tension or displacement difference between nodes. And the examples show that when the tension difference of the adjacent suspenders to the damaged one was used to identify damage, the accuracy of the result is the highest. And the result precision is decreased with the distance increases between the suspenders and the damaged one. The method using the changes of vertical displacement difference between nodes to identify suspender damage is practical and reliable.4) For suspender tension test problems, the implicit expression between the vibration frequency and suspender tension is set up which has consider the influence of elastic support, additional quality and others complex boundary conditions. The expression is high precision and applicable to long and short suspenders, but the form is complex. So the simplified calculation formula has been studied with the normal boundary conditions. For convenience in engineering application the explicit expressions are proposed under the complex boundary conditions of elastic support, additional quality and others based on Rayleigh theory. And different vibration mode function is used to derive the relationships between the suspender tension and the vibration frequency. Finally, an example is used to verify the accuracy of the various expressions. And the application characteristics, differences of the expressions have been analyzed too.5) According to the characteristics of the half through or through CFSTAB the process of health monitoring has been illustrated, and the composition and characteristics of bridge health record indexes have been explained. Zhengzhou Yellow River Bridge is taken as an example to illustrate implementation of health assessment to through CFSTAB.