Refined fatigue damage assessment of RC beam based on fractal characteristics of cracks

In order to overcome the shortcomings of traditional damage test and detection methods in terms of accuracy and practicability, and measure the cumulative damage of beam structure due to fatigue load accurately and quickly, the method to extract the fracture characteristics and dimension of cracks on key parts of bridge based on fractal theory and image processing technology is proposed. To establish the functional relationship between the fractal box dimension of cracks and typical mechanical parameters, the fatigue loading test of T-type RC simple supported beam is carried out. The relationship between different fatigue loading and damage states is established, the matching relationship between the fractal dimension and the damage index such as mid span deflection, first-order frequency and static and dynamic stiffness is clarified. The results show that the fractal dimension can be used to reveal the crack development and structural damage evolution process. The relationship between the mechanical parameters and the fractal dimension is obtained by establishing the precise empirical function which provides a new idea and method for the fine evaluation of beam damage under different damage states, and it has good accuracy and robustness. This study can provide strong support for the rapid assessment of the evaluate beam fatigue damage quickly and effectively.