Expansion Joints

Expansion Joints

An expansion joint or movement joint is an assembly designed to safely absorb the temperature-induced expansion and contraction of construction materials, to absorb vibration, to hold parts together, or to allow movement due to ground settlement or earthquakes.

In building construction, an expansion joint is a mid-structure separation designed to relieve stress on building materials caused by building movement induced by:

  • – Thermal expansion and contraction caused by temperature changes
  • – Sway caused by wind
  • – Seismic events
  • – Static load deflection
  • – Live load deflection

Because the joint bisects the entire structure, it marks a gap through all building assemblies–walls; decks; plazas or split-slab concourses; foundation floors and walls; roofs, planters, and green roofs; fire-rated demising walls and floors; interior floors; etc.  This gap must be filled to restore the waterproofing, fire proofing, sound proofing, air barrier, roof membrane, trafficable surface and other functions of the building elements it bisects.

Expansion joint systems are used to bridge the gap and restore building assembly functions while accommodating expected movements.

The term “movement joint” has been widely adopted in preference to “expansion joint” as it more appropriately encompasses the fact that building movement results in both compression and expansion of the material installed.

 

For example, when a structure heats up, the building materials from which it is built expand. This causes the “expansion joint” to close down, thereby compressing the expansion joint system installed in the gap.

 

Conversely, when the temperature drops, the materials cool causing the joint gap to open. This requires the expansion joint material to expand to follow the joint movement.

Types of Expansion Joints

  • The basic type of expansion joint. For this type, thrust generated by internal pressure is applied to the fixed points.
  • If high internal pressure is applied, a reinforcement ring is used to prevent deformation of the bellows. Three types of shapes are available.

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