The Arm (or stub and arm) which joins in the cavity and supports the whole structure of the balcony. The structural performance and the longevity of these components are paramount to a good balcony. These components must be fabricated in accordance with BS EN 1090 CE Marking requirements.
Whilst traditional bolt-on balconies connect directly to a stub, part of the secret to enabling rapid install is in the simplistic addition of arms. The one-piece arm is more efficient, more cost-effective and slightly more rigid than the two-piece (stub and arm). However, the choice of one piece or two-piece arms is mainly one which needs to be made with consideration of the interface of the arms around other trades on site.
These arms, or stubs, can be preassembled to enable them to be cast in along with the anchor as the RC frame is poured, with the arm being added later if it is thought that they may conflict, or adversely affect other trades.
Arms are typically made from galvanised steel universal beams (or ‘I beams’). The size, weight, and the thickness of the back plate of the beams is governed by several factors including the spacing of arms, the balcony projection, slab thickness, etc.
We are happy to offer the Sapphire StubGuard™ firestop as an option on your project for thermal and fireproofing around the stub.
One Piece Arms
Advantages of one piece arm
- Fewer joints mean a more rigid balcony. Not having a stub, increases rigidity.
- Reduces cost and programme on site as no additional sections manufactured or installed, the one piece arm can be factory assembled to anchor and cast-in as one complete piece.
- Can be used to support scaffold boards if positioned at approx. top of the slab, however, they are not designed to take scaffold loadings
Considerations for one piece arms
- Large sections mean consideration needs to be given to edge protection and form work during the concrete casting stage
- One piece arms typically project from the façade for the full projection of the balcony so can be prohibitive to a mast climber access strategy
- If using system scaffold or arrangements at circa 2m brick lifts, consider whether arms will pose a potential obstruction to scaffold working area.
Two piece arms
Advantages of two piece arm
- Short arms protrude just past the façade and allow mast climber access.
- Stubs can be utilised as tie points for mast climbers to avoid additional façade penetrations and infill work as the mast climbers are dismantled.
- Short stub avoids scaffold or formwork complications
- Loads from interfacing items (e.g. mast climbers) must be considered, as brackets are only designed to take balcony loads.
Considerations for two piece arms
- If you want the most rigid balcony possible you should strongly consider using a one piece arm which results in fewer joints and therefore less movement.
- A one piece arm is the more cost-effective, as they have less fabrication and less installation work.
- Loads from interfacing items (e.g. mast climbers) must be considered, as brackets are only designed to take balcony loads