What are expansion joints?

Did you know that bridges can grow? Not by much, but if you walk along one of Rochester’s bridges on a hot day it will be a tiny bit bigger than if you visit on a cold day.

This is because bridges – like everything else – are affected by temperature. We’re simplifying this a little (a lot) but when it’s very hot the bridge will expand, and when it’s cold the bridge will contract. However because each end of these structures is attached to the ground at a fixed point, this could cause a lot of problems if it meant the bridge was pushing and pulling at its abutments (where the structure meets the ground).

Civil engineers have therefore had to come up with an effective way of ensuring bridges do not bend out of shape when they are affected by seasonal variations in temperature. The answer is expansion joints.

On Rochester’s bridges the expansion joints are two strips of metal (steel), with a small gap in the middle that contains elastomeric material (a type of plastic that acts in a similar way to rubber). There are six of these on the New Bridge, and they are designed to allow the structure to expand or contract without cracking the concrete.

Next time you cross a bridge and see what appears to be a join across the deck, you’re probably looking at an expansion joint.