Slabs at isolation joints must be free to move horizontally but not vertically. True or false.

Slabs at isolation joints must be free to move horizontally but not vertically. True or false.

• A. True
• B. False
• C. Sometimes
• D. Not specified

Answer: (B)

Isolation joints are meant to let slabs move freely so they don’t transfer restrained forces between elements. That movement isn’t limited to just one direction—the joint must accommodate movement in the plane of the joint (horizontal) and also allow vertical separation if one side settles or heaves relative to the other. If vertical movement were restricted, differential settlement or temperature-induced shifts could crush or crack the joint edges, causing damage to the slabs. In practice, the joint filler and lack of dowels across the isolation joint are chosen to avoid restraining any relative movement, so the slabs can adjust in all directions as needed. Therefore the statement is not correct.

Isolation joints are meant to let slabs move freely so they don’t transfer restrained forces between elements. That movement isn’t limited to just one direction—the joint must accommodate movement in the plane of the joint (horizontal) and also allow vertical separation if one side settles or heaves relative to the other. If vertical movement were restricted, differential settlement or temperature-induced shifts could crush or crack the joint edges, causing damage to the slabs.

In practice, the joint filler and lack of dowels across the isolation joint are chosen to avoid restraining any relative movement, so the slabs can adjust in all directions as needed. Therefore the statement is not correct.