Joints

Summary

Joints - Vertical discontinuity provided in a floor slab to allow for construction and/or relief of strains. The terminology relating to the various types of joint is complex, and reference may be made to the definitions of individual joint types

Technical Information

The number and type of joints in a floor will depend on the floor construction method and its design and the chosen method should be related primarily to the planned use of the floor. Joints can be a potential source of problems because the edges of slab panels are vulnerable to damage caused by the passage of materials handling equipment, with wider joints particularly susceptible. Joints will need to be maintained during the life of the floor.

Joints are provided for two reasons:

To relieve tensile stress induced by drying shrinkage or temperature changes
To cater for breaks in the construction process

Joints in concrete floors are created in two ways:

Sawing
Forming, with temporary demountable formwork or permanent proprietary joint systems.

Expansion joints are not used in internal floors except those subject to above-ambient temperatures and to large temperature fluctuations. In most floors, the dominant movement is that caused by drying shrinkage and any ongoing thermal-related movements are much smaller. Cold store floors have greater thermal movements but the slabs do not expand beyond their as-constructed dimentions. Therefore expansion joints are not required. Designers should satisfy themselves that there is a definite need for expansion joints, avoiding their unnecessary installation and the resulting wide gap required between floor panels. Expansion joints require the provision of compressible filler and load transfer by debonded dowels or other mechanisms.