A method for testing a structure mode of vibration based on digital image recognition, being performed by a system for testing a structure mode of vibration based on digital image recognition including a camera (1), targets (2), a bridge (3), a vertical acceleration sensor (4) and a lateral acceleration sensor (5), where the camera (1) is arranged near a bridge head of the bridge (3), the bridge is equipped with a plurality of targets (2) equidistantly inside guardrails on both sides, and the vertical acceleration sensor (4) and the lateral acceleration sensor (5) are fixedly arranged on the camera (1), comprising the following process that:
- the camera (1) captures images containing all targets (2) in real time, and the vertical acceleration sensor (4) and the lateral acceleration sensor (5) monitor the vibration of the camera (1) itself in real time;
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- when the bridge (3) is subjected to random excitation to produce vibration, the targets (2) and the camera (1) vibrate together with the bridge (3), and the lateral vibration curve, longitudinal vibration curve and torsional vibration curve of the bridge (3) are calculated by the images containing the targets (2) and the camera (1) vibration information to realize the testing of bridge (3) vibration,
- wherein the process of calculating the lateral vibration curve, longitudinal vibration curve and torsional vibration curve of the bridge (3) by the images containing the targets (2) and the camera (1) vibration information comprises:
- capturing the center of each target (2) from the images containing the targets (2), obtaining the pixel displacements of the target (2) center at different moments, and converting into a unit of length, and then obtaining the lateral relative vibration displacements and longitudinal relative vibration displacements of the measuring points where the targets are located;
- unifying the units of the lateral relative vibration displacement and longitudinal relative vibration displacement of each target (2) and the units of the lateral relative vibration displacement and longitudinal vibration displacement unit of the camera (1), and subtracting the reverse displacement caused by camera vibration from the relative vibration displacement of the measuring point to obtain the absolute vibration displacement of the measuring point;
- drawing a lateral time history curve and a vertical time history curve of the measuring point corresponding to each target;
- using the lateral time history curve and the longitudinal time history curve of the measuring point corresponding to each target to obtain the natural frequency of each order, and obtain the lateral vibration amplitude-frequency characteristics and longitudinal vibration amplitude-frequency characteristics of the bridge (3);
- calculating the real-time torsion angle of the measuring point and drawing a time history curve through the longitudinal absolute vibration displacements of measuring points of the two lateral targets (2) in the longitudinal direction of the bridge (3), and obtaining the torsion amplitude-frequency characteristic curve of each measuring point by using the real-time torsion angles and time history curves of all measuring points;
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- using the obtained torsion amplitude-frequency characteristic curve of each measuring point to obtain the lateral vibration curve, longitudinal vibration curve and torsional vibration curve of the bridge (3).