Subject and Keywords:
Steel-ground structures are more susceptible than other bridges to the forces associated with their operation. Among the most difficult forces to measure and interpret are those which cause the occurrence of rapid movements. Electronic sensors are normally used for the evaluation of such movements, such as accelerators, distance meters, LVGT etc. Classical surveying methods make it possible to carry out precise displacement surveys using a "tracking" mode, several times per second, and these can therefore be used to study movements at a frequency of 1 Hz for a range of displacements of at least 1 mm. A higher frequency of registration, while simultaneously increasing the number of measured points, is possible using a photogrammetric method. In the classical sense, photogrammetry is a technique for determining specific geometric features based on measurements of points on images of an object and their mathematical processing. Currently, images are made using widely available high-resolution digital cameras, allowing images to be captured at the desired distance, with good image stabilization and short exposure time. In this paper, we present investigations using a method of measuring these rapid movements with one or more cameras and a variable number of lighting targets. This method includes the installation of lighting for the object, stabilization of the cameras, image capturing and automatic processing. Each measurement is performed using image-matching algorithms and refers to several (at least two) fixed points in the object space. This method was tested on following real objects: (1) a railway bridge during the passage of a number of trains at different speeds; and (2) a rotating footbridge. Objects were photographed using a PointGrey Black Fly camera from a distance of less than 50 m and with a frequency of 50 Hz. The results are presented in the form of two-dimensional displacement vectors of four points with a precision of ±0.5 mm. The course of the measurement and the evaluation of the results indicate the high potential of the method in studying the dynamics of flexible structures. In conclusion, it was stated that the described solution is a concept and is to serve as an inspiration for particular applications. It is now the subject of further development.