Did you know bridges move? We’re not talking lifting themselves up and walking to a different location (although that would certainly be a sight worth seeing), but bridges – like many other built structures – are not completely static.
This is because they are affected by many things. One example of this is thermal expansion, or more simply put the seasons and the weather. When the sun shines on metal it heats up and expands, and when the temperature drops the metal contracts.
This expansion and contraction is a natural process that’s managed by the inclusion of expansion joints across the width of the bridge. You can find out more about expansion joints by following the link to this article.
Movement is part of the every day life of Rochester Bridge, which means it’s also part of the net zero carbon maintenance programme. A lot of the standard maintenance simply means having eyes on the bridge, people who walk over and under it, inspecting and checking and carrying out routine activities picking up on small things and preventing them from becoming big things.
However, the human eye can’t detect thermal expansion, and so we use specialist monitoring equipment.
Rochester Bridge (comprising the Old Bridge, the Service Bridge and the New Bridge) is periodically fitted with sensors to take very small measurements for us to compare results over time.
At the moment we have two different types of sensor in place: linear potentiometers and laser tiltmeters. It’s been commented these sound like magicians’ tools, so if you want to preserve the magic of bridges, look away now.
Potentiometers measure movement along a single axis, so in one direction, while tiltmeters measure changes in vertical level. These relatively small devices are all attached in hidden areas below the deck of the bridge, because this enables us to get accurate readings without compromising the beauty of the bridges.
The combined result of their monitoring is helping us to build an ongoing picture of all movement, so we can compare normal activity over time and quickly spot anything unusual.
Finally, it’s worth a reminder that all of this monitoring and maintenance is carried out to the highest possible standard and at no cost to the public. This is because Rochester Bridge is owned and maintained by a medieval charity, the Rochester Bridge Trust, with all of its work funded by an estate that was established more than six centuries ago.