Structural monitoring

There is growing activity in the field of structural monitoring. In fact, the Video Gauge was originally invented to monitor the movements of a long-span suspension bridge. The Video Gauge has applications wherever there is a need to monitor the long-term performance of large-scale structures. Some example application areas include:

• Bridges
• Railway infrastructure
• Aircraft
• Power stations

The Video Gauge offers continuous 24/7 monitoring of:

• Displacement
• Velocity
• Rotation
• Bending

The voltage input/output module provides a versatile interface between the Video Gauge and existing sensors, data-loggers and monitoring equipment. The output of other sensor can be fed into the Video Gauge where they are logged along side the Video Gauge’s own measurements. The module’s voltage outputs can be driven from any of the Video Gauge’s measurements and fed into existing logging or monitoring equipment.

Case studies

	Accuracy of Video Gauge for displacement measurement Precise measurement of displacement is traditionally achieved using devices such as a Dial Test Indicator (DTI) or a linear variable differential transformer (LVDT). The aim of this experiment is to validate the Video Gauge as a method for measuring displacement by comparing it directly with a calibrated DTI.
	Measuring changes in wing shape in a wind tunnel Tests on a compliant wing that changed shape depending on the air flow over it required that the changes in shape be determined as the wind tunnel testing progressed. The changes had to be measured without influencing the air flow. At the same time the strains within the special core material that supported the wing skins had to be measured to check that it was behaving in the expected way (negative Poisson's ratio).
	Tracking water level in the test of a tuned liquid damper A tuned liquid damper is a simple way of reducing the response of a building to dynamic loads such as earthquake shocks. It consists of a tank of water with the depth to length ratio set so that the natural frequency of the water sloshing in the tank matches that of the structure. The Video Gauge was used to monitor the depth of the water with time as well as the pendulum displacements of the plate and the displacements of the support frame.
	Use of the Video Gauge in structural monitoring The deformations of long span bridges and similar structures need to be monitored to ensure their structural health. This can be done using an array of accelerometers but these suffer a baseline drift over time limiting confidence in their long-term outputs. A non-contacting system is to be preferred as this can eliminate this drift and allows a more direct measurement of movements in the structure.