Effect Study Of Cable Damage To Structural Performance Of The Cable-stayed Bridge

The health monitoring of long-span cable-stayed bridge is aimed at the real-time monitor and research to structural performance under the action of the working environment, external loads, and evaluation to security, applicability and durability. It provides the basis for the transportation management, maintenance, reliability evaluation and scientific research of the bridge. But many problems about structural component of cable-stayed bridge are not solved thoroughly, such as stress characteristic, damage reasons and mechanism, especially to stayed cable, its damage mechanics and damage effect to structural performance in static and dynamic, and also its fatigue stress and fatigue reliability evaluation, etc. All of these affect the further development of health monitoring of cable-stayed bridge. Taking the Runyang Cable-Stayed Bridge as an engineering background, this dissertation studies the key problems above from structural health monitoring system of cable-stayed bridge, the main contents include the followings:1.The functions and load characteristics about tower, girder and cable of cable-stayed bridge, are analyzed, and the main reasons of cable damage are summarized. The vibration types causing cable fatigue damage are presented, especially, the condition and mechanism of rain-wind induced vibrations are analyzed detailedly, which generates more hazards to cable. Based on the conclusion above, non-linear vibration characteristic of cable is studied, and a set of governing equations of non-linear vibration of an inclined cable is built according to the vibrating characteristics of small sag cable, the averaging method is used to solve approximately the equation, and the non-linear vibration response of cable is obtained.2. Field measures of the dynamic characteristics of tower, girder and cable of the Runyang Cable-Stayed Bridge, are finished, which provide initial data to the structural health monitoring system, these data can be used to diagnose, forecast and evaluate damage under the action of various disaster.3. According to results of field measures, by utilizing sensibility theory based on dynamic characteristic, the finite element model of bridge is updated, and the refined model is built, its results of modal analysis have agreement with the results of field measures.4. Base on the bridge finite element model built, variation characteristics of structural static and dynamic performance are analyzed due to cable damage. Select Young's modulus as damage variable, by its reduction, cable damage is simulated. Abundant numerical simulation is given to simulate the different cable damage locations and different damage grades in the same location, the variability of structural static and dynamic characteristics under normal conditions and cable-damage conditions are compared. According to these characteristics, a set of cable monitoring project is put forward.5.Based on the characteristics of the Runyang Cable-Stayed Bridge, and principal similar conditions, a cable-stayed bridge test-model is built. Its ratio is 1:60, the main span of model 6.78 meters, the side span 2.73 meters, and the total length 12.64 meters. In order to study the cable damage effect to structural static and dynamic performance of the cable-stayed bridge, by simulating different damage locations, cable stresses, girder flexibilities, and girder dynamic characteristics of test model are measured. By analyzing the variation rules of test data and comparing with the theoretic result, respectively, static and dynamic strategies to monitor cable damage are extracted, which provide idea to put in practice in the healthmonitoring system of bridge.6. Based on gray system theory, a gray reliability model of generalized-stress and generalized-strength is built, and gray reliability index is deduced, which includes a unknown valueλ. By using fuzzy judge theory of Fuzzy Mathematics, the best value ofλis gotten according to the property of normal distribution function, by this way, generalized-stress and generalized-strength are made white. Utilizing the gray reliability index deduced, cable fatigue stress reliability evaluation of Runyang Cable-Stayed Bridge under normal condition and cable-damage conditions are completed. Lastly, according to design target reliability index, the critical stresses of cable damage are obtained.