An expansion joint is a deliberate gap through a structure that divides it into independent sections, so each section can expand, contract and shift without cracking itself or its neighbors.
Parking structures need them more than most buildings because their decks are exposed to sun, cold and seasonal temperature swings, and because concrete shrinks and creeps over time. Joints are commonly considered once a structure grows beyond roughly 200 to 300 feet in length, with the exact spacing depending on the structural system, restraint and climate. See structural systems.
Common joint types
- Compression seals, preformed elastomeric sections squeezed into the gap.
- Strip seals, a rubber gland held in steel or aluminum edge rails, for larger movements and heavy traffic.
- Sealant joints for small movements.
- Cover plates where pedestrians or vehicles cross a wider gap.
Maintenance
- Joints are among the most common sources of leaks and the most frequent repair items in a garage.
- Leaking joints carry deicing salts into the structure below. See chloride-ion contamination.
- Seals wear out from traffic, snowplows and UV and need regular inspection and periodic replacement.
The Parkonomics view
Every expansion joint is a future maintenance item, so designers try to use as few as the structure allows. The ones that remain deserve a line in the annual budget, not an emergency.
Related terms: Chloride-Ion Contamination, Structural Systems of Parking, Post-Tensioned Concrete, Precast Concrete, Deflection, Spalled, Out-of-Phase Movement