  Image-based vibration mode identification gained increased attentions in
civil and construction communities. A recent video-based motion magnification
method was developed to measure and visualize small structure motions. This new
approach presents a potential for low-cost vibration measurement and mode shape
identification. Pilot studies using this approach on simple rigid body
structures was reported. Its validity on complex outdoor structures have not
been investigated. The objective is to investigate the capacity of video-based
motion magnification approach in measuring the modal frequency and visualizing
the mode shapes of complex steel bridges. A novel method that increases the
performance of the current motion magnification for efficient structure modal
analysis is introduced. This method was tested in both indoor and outdoor
environments for validation. The results of the investigation show that motion
magnification can be an efficient tool for modal analysis on complex bridge
structures. With the developed method, mode frequencies of multiple structures
are simultaneously measured and mode shapes of each structure are automatically
visualized.
