Restrained Movement Joints

Summary

Restrained Movement Joints - are provided in fabric reinforced floors to allow limited movement to relieve shrinkage-induced stresses between two adjacent floor panels.

Technical Information

In a restrained-movement joint steel reinforcement provides load transfer across the joint. It is assumed that when the joint opens, the steel yields.

There are two types of restrained-movement joints:

In an induced restrained-movement joint, the slab’s reinforcement fabric can continue across the joint.
In a formed restrained-movement joint, deformed bars are set in the concrete across the joint to provide load transfer between the two slab sections, as the fabric reinforcement does not continue through the joint.

The area of reinforcement provided by the deformed bars and fabric is equal throughout the floor. The area of the steel reinforcement is usually 0.08-0.125% of the slab cross section.

If a joint is:

Under-reinforced: there is a greater chance of wide joints developing as the reinforcement wouldn’t be able to resist shrinkage. Vertical deflection could also occur.
Over-reinforced: there is a risk of mid-panel cracking occurring as the steel may not yield at the joints.