3.11 Wind Load/Span Graphs – Designs to AS/NZS1170
Wind load/span graphs allow designers to ascertain spanning ability and fastener spacing requirements for designs outside of NZS 3604. They should be read in conjunction with the point load limitations appropriate to the degree of traffic predicted on the roof.
NZMRM wind uplift resistance testing specifically assumes fasteners are permanently fixed to the purlins and will not pull out. Because of this and, also due to the huge range of fastener/purlin material variations, the pull-out resistance of fasteners is eliminated from the uplift testing procedure. Accordingly, when designing for SED wind conditions, the engineer must make a separate calculation to determine the necessary pull-out resistance of the fastener from the purlin material to be used, which will allow the correct selection of the fasteners.
The performance of profiled metal cladding depends on the profile shape, thickness of the metal, the span, and the fastening type and pattern. These values can be greatly enhanced by using load spreading washers or thicker material.
All the tests from which these graphs have been derived used the 2:3 ratio of end to intermediate span and the graphs shown are for intermediate spans only. End spans must be reduced by two-thirds for these values to be assumed.