Bridge Damage Identification Research Based On Modal Strain Energy

Based on analyzing the present researches and existing problems of the dynamic method of the damage detection in bridge structures, the systemic researches was applied for locating the damage of a concrete beam, concrete plate and concrete bridge using the dynamic nondestructive examination method. The energy method is applied to derive the natural vibration frequency and mode shape for a simply supported beam and simply supported plate before and after damage.Based on the basic theory of element modal strain energy change and structure shape change before and after damage, the damage index was put forward to locate structure damage, the basic formulas are obtained firstly to identify the damage location and discriminate qualitatively the damage degree for beams and plates, and the program is compiled in calculating the damage index for beams and plates.The damage index is used to identify the damage in a concrete beam and a concrete plate in the numerical simulation and calculation analysis. The numerical results show that the damage location can be identified exactly calculated using the first mode, the first five modes or the first nine modes if there exists one or two damages and also there has the different damage degree. The damage index value is the largest at the damage location, and the damage index value would be increased using the same account mode to calculate as the damage degree gets larger. So this damage index can be used to estimate the damage degree qualitatively. Moreover, an experiment for a two-span continuous beam has be made to testify the efficiency of this method, and the experiment results indicate that the ideal results can be obtained to testify the damage location by using the first five modes from the experiment data.With the help of structural calculating software ANSYS, damage simulation and identification have been made for a variable cross-section pre-stressed continuous bridge and the effect of random noise was added. The results show that the damage location can be identified effectively to calculate and analyze using the first mode, the first three modes and the first five modes if there have the different damage locations and degrees. Similarly the damage index can be also used to estimate the damage degree qualitatively. The same conclusion could be obtained when considering the influence of the random noise.