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Decking for curved roofs

6 March 2012 No Comment

Curved roofs require special consideration when selecting a suitable deck profile. Trapezoidal profiles are particularly rigid in the longitudinal axis, resulting in minimum radii requirements. The stated radii are recommendations, to prevent possible buckling of the profile webs. Slightly tighter radii may be achieved, if distortion is not a major concern, i.e. if a separate ceiling is to be installed. The minimum radii given in the above table applies to plain and web perforated decks.

Decks should be installed in multi span condition, with purlins at reduced support centers to assist the deck being pulled down to the curve. Typical purlin centres of 1800 mm should be reduced to 1200 mm to 1500 mm maximum centres. Deeper decks spanning over main steelwork can be supplied up to 12 metres long. For multi span condition, this limits the span to 4000 mm maximum.

Table

Tight radii, generally for curved eaves, can be achieved on D35 and D46 decks by crimping the profile within the factory. This does however impose maximum arc length requirements, for manufacture, of 4500 mm. The curve radii is determined from the force applied to produce the indentation, or crimp, and the spacing of the crimps. Typically one crimp will turn the profile through
an angle between 2 to 5 degrees.

As a secondary operation this adds to the manufactured costs, as well as extra costs for transportation. To avoid unnecessary costs, tighter than recommended radii can be achieved by installing the deck in single span condition, i.e. to produce a facetted curve. Dependent on the orientation of support structure this could result in a point bearing contact. This must be avoided by
the addition of a timber fillet, as indicated, ensuring that full bearing support is maintained. Fasteners solely into timber must be austenitic stainless steel, with an embedment depth of 40 mm.

build up

The ideal method to form a curved roof is to install the deck perpendicular to the curve direction, i.e. allowing the deck to naturally curve in its weak axis. This allows for the ability to form tight radii from straight profiled decks.

With careful design it is possible to produce complex curves in both directions, as indicated for the Sage Music Centre, Gateshead.

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