What is a finger expansion joint?
A finger expansion joint is an expansion joint in a bridge deck or viaduct, made up of two rows of interlocking projections that look like fingers. In Dutch it is called a vingervoeg. The projections are also called joint teeth. They are usually made of steel and are anchored on either side of the joint. Traffic drives over it, while the bridge deck underneath can move freely.
Why an expansion joint?
A bridge deck expands in heat and contracts in cold. With concrete, shrinkage and creep are added to this. At the transition between the bridge deck and the abutment, or between two parts of a bridge, a gap therefore develops that constantly changes in width. An expansion joint bridges that gap, so that cars, cyclists and pedestrians can cross it safely.
How a finger expansion joint works
The fingers from both sides slide in between each other. If the deck becomes longer, they slide further into each other; if it contracts, they slide apart. The running surface thus remains virtually continuous. Finger expansion joints are used mainly for larger movements, where a simple rubber joint is not sufficient. There are also variants designed for earthquake movements.
Water and dirt fall through between the fingers. That is why there is usually a collecting trough or drainage under a finger expansion joint, so that the water does not reach the bearings and the concrete below.
Points of attention in maintenance
- Keep the drainage clean: a blocked trough under the joint causes leakage onto the bearings and abutment, with a risk of concrete damage and corrosion.
- Check the anchorage: loose or broken fingers are dangerous for traffic and cause noise nuisance.
- Cyclists and pedestrians: the openings between the fingers must be narrow enough for bicycle wheels, heels and wheelchair wheels. Cover plates are therefore sometimes used on cycle and footbridges.
Related terms
- Viaduct
- Bridge
- Movement joint
- Abutment
- Bearing
- Finger joint
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