3-D measurement of structural vibration using digital close-range photogrammetry

• We have established the process for measuring 3D vibration amplitude by using two inexpensive ordinary cameras.
• The proposed technique does not need to attach any physical sensors to the structure.
• The proposed method can remotely capture the dynamic displacements of various locations of structure vibrating in 3D.
• The proposed method can remotely capture the dynamic displacements of various locations of structure vibrating in 3D.
• An experiment was successfully performed to measure the 3D vibration displacement of a vibrating cantilever.

In this paper a methodology has been developed to measure dynamic vibrational displacements of a structure by using digital close-range photogrammetry. Consecutive stereo images of the vibrating structure with multiple target marks are obtained by two inexpensive cameras, and then the spatial coordinates of each target as a function of time are computed by applying the collinearity and space intersection theory. The proposed method can capture the displacements of various locations of a structure in 3-dimensional space, i.e., both the planar and in-depth displacements relative to the cameras, therefore, 3-dimensional dynamic motion of a structure can be easily obtained. It is not necessary to attach sensors to the structure which may cause undesired changes to the structure's dynamic characteristics. Vibrations of non-accessible facilities such as radioactive or high temperature components can be monitored remotely by using this method. The measurable frequency range depends on the number of frames per second (fps). By applying the proposed method, an experiment was successfully performed to pick up 12 Hz 3-dimensional vibration by digital cameras of 40 fps.