Use of the Video Gauge in structural monitoring

The problem

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.

The Solution

The curves shown here are for a simple pendulum, but show that deflections substantially less than 1 pixel can comfortably be tracked by the system. The approach can be applied to any structure subject to complex loadings, such as an aircraft fuselage, as well as to bridges and other civil engineering structures.

This data is taken from monitoring deck displacements on the second Severn Crossing bridge (shown above). Over short periods the Video Gauge and accelerometer readings are in good agreement, but the agreement breaks down over longer periods as the accelerometer readings drift.

Advantages of the Video Gauge

The use of the Video Gauge eliminates the problem of baseline drift with conventional double integrated extensometer readings, it also permits a reconfiguration of which parts of the structure are to be monitored with minimal effort.