Construction methods · Finishing, articulation and maintenance

Expansion joints

The gap where the deck ends and the abutment begins, bridged by a device that carries wheels and moves with the deck: buried asphaltic plugs for a few millimetres, strip seals to about 100 mm, finger plates and modular joints for 300-1,000 mm on long bridges. Joints leak, wear and are the first thing replaced; the best joint is none.

How bridges get built · Finishing, articulation and maintenance · Expansion joints

Also called: strip seal, modular joint, finger joint, asphaltic plug joint, jointless design

How it is done

Block out the deck ends to the joint detail; set the joint assembly level with the pavement, with the gap pre-set for temperature.
Anchor into the deck and backwall concrete, cast the nosing, seal; install drainage under the joint.
Modular joints: install as a unit with support bars and control springs; check the seal and the bearings of the bars.

Where it fits

Bridges over 60-100 m, or shorter ones with high skew or curvature; joint type by movement range.

Where it does not

Joints over piers and bearings without drainage (every leak corrodes the bearing below); modular joints where a series of strip seals would do.

Plant, pace and money

PlantSaws and breakers for the blockout, small crane for modular units.

ProductivityA joint in two to five days.

CostStrip seal USD 1,500-3,000 per metre; modular USD 8,000-20,000 per metre; the game's upkeep score penalises modular and finger joints most.

Risks and controls

What goes wrong

Snowplough and truck impact damage, seal failure, noise complaints, fatigue of modular joint bars.

Quality assurance

Gap setting recorded with temperature, water test of the seal, drainage inspection.

Examples

Every seat abutment in the game; integral bridges avoid them entirely.