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U.D.L. Wind And Snow Loads

 

The maximum performance of plastic roof sheeting for spanning capability and deflection under a uniformly distributed load depends on the section properties and type of material of the profile. The section properties depend on the number and depth of corrugations and the thickness of the profile. (see section 3.1.2.) 
The uplift pull-through load performance depends on the number of fasteners per square metre and the type and size of the washer.

Profiles which have deeper ribs are more rigid and will deflect less, but will not provide any greater resistance to pull-over at the fixings, unless the sheet thickness is increased. Greater spans also require a thicker sheet. Additional fixings will increase resistance to pull-over failure at fixings, but will not limit deflection.

Roof lights located in the peripheral zones of high wind design load should have provision for the higher load in this area by the use of additional fixings, reduced purlin spacings or by increasing the roof light thickness. Deflection of plastic roof lighting due to UDL wind or snow loading should be limited to less than 1/30th of the span or 50 mm.

All plastic roof lighting should be tested to withstand wind loads and extrapolation is not acceptable as a statement of performance.

On buildings higher than 10 m or areas located in the peripheral zones of high wind design loads, near verges, eaves or ridges it is better practice for roof lights to be omitted.

Plastic roof sheeting must match the design load of the adjacent metal roof cladding. This can be achieved by using a mid-span support or by increasing the weight of the plastic sheet.

Excessive deflection due to long spans can open up side laps or cause failure in compression at the fixing points.

 

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