Stability and Outriggers Flashcards

What is the 'overturning moment' of a tower scaffold?

Answer: The tendency of the tower to tip over, calculated as the horizontal force multiplied by the height at which it acts

The overturning moment is the product of a horizontal force (e.g., wind) and the distance from the point of application to the tipping point (base edge). The taller the tower and greater the force, the larger the overturning moment and the greater the risk of toppling.

What is the 'restoring moment' and why is it important?

Answer: The counteracting force created by the tower's own weight about the opposite base edge that resists overturning

The restoring moment is the product of the tower's weight and the distance from the centre of gravity to the tipping edge. It must exceed the overturning moment for the tower to remain stable. A wider base and heavier tower increase the restoring moment.

When must stabilisers or outriggers be fitted to a tower scaffold?

Answer: Whenever the manufacturer's instructions require them, typically when the tower exceeds the freestanding height-to-base ratio

Stabilisers or outriggers must be fitted whenever the manufacturer's instruction manual specifies them, which is typically when the tower height exceeds the freestanding height-to-base ratio limits. The manufacturer's guidance is definitive.

What is the effect of wind on an unattended tower scaffold left fully erected?

Answer: Wind can create sufficient force to overturn the tower, especially if sheeting or boards increase the wind-catching area

An unattended tower presents a large surface area to the wind. The force can be enough to overturn it, particularly if any sheeting, banners, or unfixed materials are attached, as these act like sails. The tower should be lowered, dismantled, or tied off if left unattended in exposed conditions.

How does adding materials and tools to the platform affect tower stability?

Answer: It raises the centre of gravity and increases the overturning moment, reducing stability

Loading the platform with materials raises the combined centre of gravity of the tower system. A higher centre of gravity increases the overturning moment for any given horizontal force, making the tower less stable. This is why safe working loads must be observed.

What is a 'ballast' in relation to tower scaffold stability?

Answer: Additional weight placed at the base of the tower to lower the centre of gravity and increase stability

Ballast is weight added to the base of the tower (typically kentledge blocks or sandbags) to lower the overall centre of gravity and increase the restoring moment. It must only be used as specified by the manufacturer and must be securely fixed.