Questioning Safety: Scaffolding #6 – Structure
Is the scaffold appropriately structured?
Proper spacing and bracing are the two elements that ensure the fantastic strength of industrial scaffolds.
How?
Tubular metal scaffold posts are incredibly strong provided that the forces are exerted purely “axially” – in a direction straight down the long axis of the tube.
The posts must first be held plumb by proper bracing. Poor bracing results in unstable posts and thus – weaker scaffolds.
Second, controlling the vertical span or “lift height” also works to keep the posts plumb and true without skewing or bending while under load.
Is the scaffold braced adequately?
For scaffold towers, the structure must be braced vertically, on all four sides, and at every lift location. (i.e. entire lifts are not permitted to be left “blank” without some form of vertical bracing.
For multi-bay scaffolds, the vertical bracing patterns can be more complicated. Specific bays may be omitted (based on manufacturer’s instructions) however, entire lifts cannot be overlooked for vertical bracing.
Horizontal bracing is also required to keep the posts and structure square and true. Horizontal bracing is especially crucial on tied, enclosed and rolling scaffolds.
Vertical or horizontal bracing may be omitted only where necessary and when the strength and stability of the bracing is replaced by other means, such as a tie.
Always follow the manufacturer’s written instructions on proper bracing patterns and frequency.
Is the scaffold erected with proper lift heights?
The vertical dimension between the horizontal components (ledgers/bearers/transoms) is called a “lift height.” The generally accepted industry standard for maximum lift height is 6 feet 6 inches or 2 meters. This interval corresponds to the dimension of typical system scaffold bay braces. Shorter lift heights (1 meter or 1.5 meters) are permitted when appropriately braced – however, lift heights TALLER than 2 meters are not recommended.
Is the scaffold structure sufficient to resist excessive bending and deflection?
As noted already, the tubular scaffold component is solid enough to resist forces on its axis. However, the tube strength depreciates with additional “shear” forces. Some examples of detrimental bending could be:
- Side loads at the scaffold base. A 12,000 lb strong screw jack base can lose over half its strength with just a 300 lb horizontal load added.
- Cantilever brackets causing bending on scaffold posts. Additional supports may be required to minimize bending.
- Ties that are placed too far away from the scaffold nodes can cause post bending.
- The excessive deflection of ledgers or transoms can cause leverage (bending) around the node.
Field Questions
- Is the scaffold braced adequately?
- Is the bracing as close as possible to the node points?
- Are the vertical posts/standards plumb within tolerance?
- Are horizontal braces installed where required?
- Are the proper lift heights not exceeded (typically no more than 6 foot 6 inches or 2m)?
- Is the scaffold exposed to any possibility of excessive bending (e.g., ties or cantilevers not at node points, sloped foundations, etc.)
- Does the scaffold show any signs of excessive bending or deflection?
- If bracing has been omitted – have additional means of stability, such as ties, been installed?
- Are scaffold users well instructed that they cannot remove any braces, or other structural components unless by a Competent Person?
