Case Studies

Dynamic Movement of the Humber Bridge Rocker Bearings

15 May 2012

Arup, working for the Humber Bridge Board, wanted to know whether the rocker bearings at the Humber Bridge were moving appropriately, which meant detecting 0.3 mm of movement at a radius of about 200 mm. The Moiré Tell Tale was attached at the bearing location, the white part bent to a right angle to attach it to one part of the bearing and the transparent overlay attached to the other.

The Moiré Tell Tale was then filmed. The video showed about 3 minutes worth of movement in 30 seconds.

"The tell-tale immediately gave useful results. A 0.3 mm displacement took place over 9 seconds. This rate of movement simply cannot be observed with the naked eye and is difficult to detect (and un-quantifiable) by touch."

Dynamic Crack Movement in a Brick Arch Viaduct

15 May 2012

This case study shows a Moiré Tell Tale attached across a small crack between two rings of a brick arch. Casual observers had identified movement in the crack and suggested it was from 2 to 3 mm. The Moiré Tell Tale shows it to be actually moving less than 0.3 mm.

It also shows the movement to be entirely linear and radial to the arch. The crack opens and closes in one direction rather than in a circular or elliptical motion. That can only happen if the bricks below are being pushed down and those above are not. This proves conclusively that the rings are only separated near the edge of the arch, a fact that was confirmed by drilling cores to trace the crack.