Movement joint

A movement joint, also known as an expansion joint, is a dynamic component that is designed to relieve or absorb movement between structural elements and help prevent cracking. Such movement can be a result of thermal expansion and contraction, settlement, seismic activity, load transfer, moisture movement, chemical changes, shear movement, and so on. Movement joints are most commonly found between sections of building facades, concrete slabs, bridges, pavements, railway tracks, pipelines, and so on.

In road construction, movement joints can be provided in the transverse direction to allow the expansion and contraction of a concrete slab due to temperature and subgrade moisture variation. They are intended to prevent potentially damaging forces accumulating within the slab itself or surrounding structures.

In masonry walls, joints should be properly constructed so as to allow a carefully calculated degree of movement without the stability and integrity of the wall being impeded. They are typically formed by a gap in the masonry, filled with a compressible joint filler (such as cellular polyurethane, cellular polyethylene or foam rubber), and sealed on the outside with a flexible weather resistant sealant (such as polysulfide or low modulus silicon). They can be located at a corner but unless the masonry is suitably tied this can affect the buttressing provided by the return wall. To enable the return wall to provide sufficient buttressing without the need for additional wall ties, movement joints are typically positioned at least 550 mm from the internal corner.

Movement joints, should generally not coincide with a door or window opening. Instead, they should be positioned in sections of full-height masonry. Where this is not possible, an engineer should design the joint to avoid it passing around window and door frames.

In bridge construction, movement joints can be formed to accommodate movement in the bridge deck. For more information, see Bridge construction.

In railway engineering, jointed track consists of rail lengths that are bolted together using fishplates, that is, perforated steel plates that are usually 600 mm long and used in pairs on either side of the rail ends. Small gaps are left between rail ends to act as expansion joints in high temperatures. Jointed track requires a large amount of maintenance and does not provide as smooth a ride surface as welded rail, making it less commonly used for high speed trains.

[edit] Related articles on Designing Buildings Wiki

• Bridge construction.
• Cracking and building movement.
• Contraction joint.
• Expansion joint.
• Pavement.
• Preventing wall collapse.
• Railway engineering.
• Reversible and irreversible expansion.
• Road construction.
• Road joints.
• Settlement of buildings.
• Thermal expansion.

[edit] External references

• Designing for movement in brickwork, Brick Development Association, 2016.