JOINT (BUILDING)

A 'building joint' is a junction where building elements meet without applying a static load from one element to another.

Contents

Qualification requirements

Perimeter slab edge

Head-of-Wall (HOW)

See also

External links

Qualification requirements

Such joints are often subject to movement, as a function of the building's design basis. Firestops must be able to demonstrate the ability to withstand operational movement prior to fire testing. Firestops for such building joints can be qualified to UL 2079 -- Tests for Fire Resistance of Building Joint Systems.
Whether or not the building elements forming the joint have a fire-resistance rating, the joint design must still consider the anticipated operational movement of each joint. Timing is also important, as freshly poured concrete shrinks particularly during the first few months of a new building, potentially causing joint size changes.

Perimeter slab edge

Firestopping at the "perimeter slab edge", which is gaps between the floors and the backpan of the curtain wall or precast concrete panels, are essential to slow the passage of fire and combustion gases between floors. It is important to note that the firestop at the perimeter slab edge is considered a continuation of the fire-resistance rating of the floor slab. The curtain wall itself, however, is not ordinarily required to have a rating. This causes a quandary as Compartmentalization (fire protection) is typically based upon ''closed'' compartments to avoid fire and smoke migrations beyond each engaged compartment. A curtain wall by its very nature prevents the complete compartment (or envelope). The use of fire sprinklers has been shown to mitigate this matter. As such, unless the building is sprinklered, fire may still travel up the curtain wall, if the glass on the exposed floor is shattered due to fire influence, causing flames to lick up the outside of the building. Falling glass can endanger pedestrians, firefighters and firehoses below. An example of this is the First Interstate Bank Fire in Los Angeles, California. The fire here leapfrogged up the tower by shattering the glass and then consuming the aluminium skeleton holding the glass. Aluminium's melting temperature is 660°C, whereas building fires can reach 1,100°C. The melting point of aluminium is typically reached within minutes of the start of a fire. Sprinklering of each floor has a profoundly positive effect on the fire safety of buildings with curtain walls. In the case of the aforementioned fire, it was specifically the activation of the newly installed sprinkler system, which halted the advance of the fire and allowed effective suppression. Had this not occurred, the tower would have collapsed onto fire crews and into an adjacent building, while on fire. Exceptionally sound cementitious spray fireproofing also helped to delay and ultimately to avoid the possible collapse of the building, due to having the structural steel skeleton of the building reach the critical temperature, as the post-mortem fire investigation report indicated. This fire proved the positive collective effect of both active fire protection (sprinklers) and passive fire protection (fireproofing).

Head-of-Wall (HOW)

Where fire-resistance rated wall assemblies masonry or drywall, typically, meet the underside of the floor slab above, a movement joint results, which can be subject to compression, as the freshly placed concrete cures and shrinks all over a new building.

See also

★ Concrete

★ Penetration (firestop)

★ Sealant

★ Firestop

★ Curtain wall

★ Passive fire protection

★ Active fire protection

★ Mineral wool

★ Packing (firestopping)

★ Fire sprinkler

External links

★ UL2079 Scope: Tests for Fire Resistance of Building Joint Systems