In building construction, an expansion joint is a mid-structure separation designed to relieve stress on building materials caused by building movement. Building movement at expansion joints is primarily 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 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 joint system installed in the gap.
Conversely, when the temperature drops, the materials cool causing the joint gap to open. This requires the joint system to expand to follow the joint movement.
Expansion Joint Transitions
Expansion joint transitions are essential for ensuring a sealed, safe, and energy efficient building envelope.
Continuity of seal at changes in plane and direction, and between expansion joint systems, is achieved when factory-fabricated transition assemblies are specified and installed.
Whenever possible, transitions should be factory-welded to the ends of longest possible lengths of straight-run material. This minimizes the number of field-welded connections – saving time and reducing risk.
Collaborative 3-D expansion joint design methodology ensures that all parties involved in delivering trouble-free expansion joints works together for that shared goal.
Today it is possible for designers to wrap the entire building envelope, as well as ensure that life-safety is addressed by specifying expansion joint systems that tie into one another and are warranted for continuity of seal between like or dissimilar technologies.
Passive Fire Protection at Building Expansion Joints
Because expansion joints bisect the building, they are a literal gap in the floors, wall and ceilings of the building. A fire in one room could rapidly spread through the expansion joint openings if not properly sealed with fire-resistive expansion joint systems. Historically, these large structural openings required a fire barrier in the form of the fire blanket be looped into the joint opening to block the passage of heat, flame and smoke. The invention of all-in-one water and fire resistant expansion joints has simplified the treatment of expansion joints. Instead of multiple systems to fire-rate, bridge, and seal joints, single systems can do all three tasks. The US test standard for fire-resistive expansion joints is UL 2079 which encompasses the burn requirements of ASTM E119 and the joint cycling requirements of ASTM E1399 in the same way that ASTM E1966 does. The UL tests for applications in decks and walls differ in the requirement of a hose-stream test for wall applications to prove the structural integrity of the expansion joint seal during a fire.