Scaffold Backpropping for Hoist
Brogan Powered Access Ltd
After providing the hoist access design, noting all relevant emergency buffer loads acting on the existing structural slab, the main contractor found that the existing slab was not capable of supporting the hoist loads. The emergency buffer loads can be extremely high depending on hoist model, buffer size and emergency brake type, so this is a common occurrence when locating a hoist on an existing slab with basement levels below.
Due to the location of columns at the lowest basement level, a temporary backpropping scheme was proposed to allow install of only a single level of support which allowed the lowest basement level to be kept clear of any scaffold. The proposal required minimal deflection throughout the frame to allow transfer of loads through the existing column locations and so twin beams were utilised in the main span to provide sufficient rigidity.
A central tower was installed, jacked to the underside of the ground floor slab directly beneath the hoist buffer location. This tower was then supported by two beam systems, allowing the load to be distributed and spread sufficiently to the column locations set out by the main contractor. This not only allowed the existing slab to remain completely unloaded, but to significantly reduce the initial imposed load, providing a cost effective and efficient scheme for the site.