| Structural damage identification is the core of the health monitoring system of bridge. The purpose of bridge damage detection is to identify the location and the extent of bridge damages based on the characteristics represented by bridge. The methods of bridge damage identification mainly include three kinds such as static, dynamic and intelligent method. The theory and application of detection technique for bridge damage based on the strain mode is mainly involved in this thesis. According to the bridge mode shape change before and after damage, the difference of the strain mode change is obtained and used as the damage index to identify bridge damage.The use of central difference method for modal parameter in the strain mode method can solve the contradiction between less measure points and the guarantee of identification precision. The operation and plot program are developed by using the Excel tool. As long as lower step vibration shapes of the bridge are input, the graphic representation of damage identification and the numerical results will be obtained. In this thesis the numerical simulation and calculation analysis of the damage are presented for a simple supported beam and a continuous beam, the damage of bridge is simulated by the stiffness reduction of the element; the mode shape is computed by the software of Midas. And the strain mode difference computed by central difference method is used to identify the damage.The numerical results show that the damage of a simple supported beam or a continuous beam can be identified exactly by use of the first five modes. When the bridge is analyzed in the same order strain mode, the strain mode difference is increased with the increase of the degree of damage. For the same degree of damage, the strain mode difference is increased with the increase of the strain modal order. Therefore, the strain mode technology can be used in the damage identification of bridge; it has definite value in the bridge detection. |
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