For circular buildings the lay of decking is dependant on the orientation of support beams. They can be installed radially or laterally. For either type installation on circular buildings, sheet ends require to be rake cut.

Rake cut ends will not overlap and will be butt jointed, requiring a minimum support flange of 150mm, ie, ensuring a minimum end bearing of 75mm.

The selection of deck orientation could be decided for aesthetic reasons, however there are important structural issues which must be considered.

For circular segmented structure, it is not possible to manufacture tapered decks and rake cutting along the long parallel length is not recommended. Therefore decks must be laid as shown in the diagram below, in single span condition with rake cut ends.

Rake cut ends will not overlap, requiring butt joints with a minimum support flange of 150mm, ie, ensuring a minimum end bearing of 75mm.

Decks can only be manufactured with square cut ends. The installation contractor must provide any requirement for rake cutting on site, allowing for subsequent costs.

Typical rake cut joint indicating correct installation

• Where decks are installed with rake cut end laps, these cannot be adequately sealed for air permeability. Therefore a separate vapour control membrane layer must be installed.
• Angled rake cuts will require special rake cut fillers, to close off the wider troughs, at the building perimeter to maintain air permeability requirements.
• Where decks have to accommodate an angled end lap joint, any attempt to install decks with an overlap, instead of rake cut ends, will result in the decks not nesting as indicated below.

Deck installed incorrectly by attempting to twist overlap without rake cutting.

For further information please do not hesitate to get in touch with our Technical Department at Tata Steel, E mail: technical.structuralproducts@tatasteel.com