What is a fusible fire wall anchor?
A fusible fire wall anchor is a wall fixing with a plastic part that softens and gives way at a set temperature, so that the connection between a steel frame and a fire wall is deliberately released in a fire. If the steelwork on the fire side deforms or collapses, it does not drag the fire wall down with it, and the adjoining fire compartment stays protected for longer. In Dutch it is called a smeltanker, and the principle is the same as a fusible link.
How it works
- Make-up. A plastic clamping block with fixings such as a screw, washer and plug. Fischer describes its HDT anchor as a clamping block with a 7 x 80 wood screw, a DIN 9021 washer and an S 10 plug.
- Behaviour in heat. According to Fischer, the HDT is stable up to +50 °C, and its stability and stiffness drop noticeably from about +100 °C. Other products give way at around 180 °C. In both cases the steel frame is still stable at that point.
- In normal use. The anchor carries wind pressure and suction on the wall.
Application
Fusible anchors are used mainly in industrial and warehouse buildings where a fire wall of aerated concrete panels or masonry stands against a row of steel columns.
- Design it as a system. The wall must stay standing when the anchors on the fire side fail. Where a wall sits between two steel frames, it is anchored on both sides so the cold side holds it.
- Follow the manufacturer’s system. Use only the tested combination of wall panels, anchors and spacings.
- Have it engineered. The number and position of anchors follow from the wind load and the fire resistance requirement.
- Never substitute steel ties. A “stronger” steel fixing defeats the whole purpose.
Common mistake: using ordinary steel wall ties during alterations or repairs on a fire wall designed with fusible anchors.
Related terms
- Fire wall
- Fire compartment
- Fire resistance
- Shear bolt
- Tilting nib
- Aerated concrete
- Skeleton frame construction
Want to know more about building terms? Visit our knowledge base at fredsdiyplans.com.