Strain-Based AOMA of a Vierendeel Truss Bridge

Strain-based monitoring methodologies can offer the crucial advantage of early stage damage detection due to the large effect that damage can have on the strain field in its immediate vicinity. For this reason though, a dense sensor grid is required that is able to provide relevant information at several critical locations of a monitored structure. In this paper, a strain-based methodology is employed for monitoring a historical Vierendeel truss bridge. The strain measurements are conducted with a dense grid of fiber Bragg gratings that measure ambient and operational dynamic strains. The measured strains are used in Automated Operational Modal Analyses to obtain the modal characteristics of the bridge, i.e., strain mode shapes, natural frequencies and damping ratios. The performance of the methodology in monitoring critical locations of a structure that can be subjected to fatigue and other relevant types of damage is tested for the first time. The sensitivity of the modal characteristics to temperature and loading amplitude is also investigated.