A movement joint, also known as an expansion joint, works by creating a designed gap or break in a structure to accommodate movement caused by temperature changes, settlement, or other factors, preventing stress buildup and potential damage.
Here's a breakdown of how they function:
-
Purpose: Movement joints are strategically placed gaps within a structure. These gaps allow individual sections of the building to expand, contract, settle, or vibrate independently.
-
Accommodation of Movement: Different building materials react differently to environmental changes. For example, concrete expands and contracts with temperature fluctuations. Without movement joints, these expansions and contractions would create internal stresses, leading to cracking, buckling, or other structural failures. The joint accommodates these movements.
-
Types of Movement: Movement joints handle various types of movement:
- Thermal Expansion/Contraction: Changes in temperature cause materials to expand and contract.
- Settlement: The ground beneath a structure can settle unevenly, causing stress.
- Seismic Activity: Earthquakes cause structures to move and vibrate.
- Moisture Expansion/Contraction: Some materials expand and contract with changes in moisture levels.
-
Design Considerations: The size and placement of movement joints depend on several factors:
- Type of materials used: Different materials have different coefficients of thermal expansion.
- Climate: Areas with large temperature swings require wider and more frequent joints.
- Building size and shape: Larger and more complex structures need more joints.
- Soil conditions: Unstable soil requires joints to accommodate settlement.
-
Materials used in movement joints: Various materials are used to fill the gap in a movement joint, allowing for movement while preventing water and debris from entering. Common materials include:
- Elastomeric sealants: Flexible materials that can stretch and compress.
- Foam fillers: Compressible materials that provide a backing for sealants.
- Joint covers: Metal or plastic strips that bridge the gap while allowing movement.
-
Example: Consider a long concrete sidewalk. Without expansion joints, the concrete would crack as it expands in the heat of summer. The expansion joints, typically small gaps filled with a flexible material, allow the slabs of concrete to expand without pushing against each other with excessive force.
In essence, movement joints are pre-planned cracks that control where movement occurs, preventing uncontrolled cracking and structural damage.
