Camera-Based Vibration Measurement of the World War I Memorial Bridge in Portsmouth, New Hampshire

Structural health monitoring (SHM) is a method for determining the structural integrity of civil infrastructure elements as a basis for maintenance and repair protocols. This monitoring depends on collecting structural response data from sensors installed on the structure due to in-service excitations. The installation additionally requires access to structural elements, power, and communication. New methods for remote measurement of displacements using video cameras could greatly simplify the process of instrumentation, making SHM much more attainable for many structures. This paper presents the remote camera measurement of the motions of the World War I Memorial Bridge in Portsmouth, New Hampshire, a vertical-lift bridge, from a distance of over 80m. Vibration frequencies and mode shapes of the bridge are identified by measuring the displacements due to the lift span impact. Displacement of the bridge due to in-service traffic is also measured. Measured signals are compared with those from accelerometers and strain gauges installed on the bridge, and identified characteristics of the bridge are compared with a finite-element model for verification. Results show the potential of applying video cameras to measure and visualize vibrations of structures in SHM.