In design phases, expansion joints are required to have which attribute?

• A. Bearing capacity for static and dynamic loading
• B. Movement capacity
• C. Water-tightness
• D. Traffic safety

Answer: (B)

Expansion joints are included to let parts of a structure move relative to each other without transferring that movement into the rest of the system. The key attribute they must provide is movement capacity—the ability to accommodate the expected relative displacement in the joint interface. This movement comes from thermal expansion and contraction, shrinkage, settlement differences, and dynamic actions. If the joint cannot absorb these movements, cracks, joint binding, or structural damage can occur, making the joint fail.

While features like water-tightness or safe operation under traffic are important in practice, they depend on having sufficient movement capacity. A joint that can’t accommodate the anticipated movement cannot function properly, no matter how watertight or robust it is in other respects.