COP v3.0:structure; fastener-loads

3.11 Fastener Loads 

Fastener design aims to avoid strength failure of the screw before failure of the sheeting or the structure. Most fastener failures happen due to negative load (or uplift) and testing procedures are designed to closely simulate these conditions.

Fasteners used to fix metal cladding can fail by pulling out of the structure or by shearing. The cladding can fail by pull-over or profile collapse.

Fastener design should be sufficient to avoid pull-out and prevent deformation of the cladding around the fastener heads that can cause leaks.




3.11.1 Load-spreading Washers 

Profiled load-spreading washers spread high wind uplift-loads over a larger area around the fastener head. Using load spreading washers under the fastener can increase the load resistance of each fastener by up to 50%.

The type, size and stiffness of washers are critical for performance. Where performance data incorporating load-spreading washers is used, the specification of the washer must be quoted with the fastener.

In general, load-spreading washers should have a minimum thickness of 0.95 mm for steel and 1.2 mm for non-ferrous metal.



Where oversized holes are used to accommodate thermal movement of the sheeting, load-spreading washers should be used with sealing washers to ensure weather tightness.