COP v3.0:testing; background-scope

17.2 Background to Scope 

C1.1. GENERAL

There is no specific New Zealand Standard (NZS) for testing sheet roof and wall cladding, and testing has been carried out using requirements and methods based on the Australian Standards AS 1562.1 and the AS 4040 series. These Standards are interrelated and AS 1562.1 sets out the performance requirements to be achieved using the test methodology of AS 4040.   

While the adoption of the joint Loadings Code AS/NZS 1170.2  - Structural design actions (in many revisions), has resolved many of the issues relating to the determination of wind forces on buildings, New Zealand and Australia use somewhat different testing methods and performance benchmarks, although still based on AS 4040 and providing complance with AS/NZS 1170.2.

C 1.2 Provision for variability of results

AS 1170.0 provides in Table B1 a method of depreciating test results based on the number of test repeated and the inherent variability of the product (Coefficient of Variability). Extensive testing has been carried out in New Zealand over many years, and where replication of tests has been carried out, the variability due to materials has been negligible. Concentrated load results are very consistent as are those from top fixed steel roof and wall cladding and from the results of hundreds of previous tests the Coefficient of Variation (COV) for these tests can be assumed to be taken as less than 5%.

For self-supporting and fully supported secret-fixed roof and wall cladding the variability which occurs from small but significant differences in profile or clip tolerances means that a greater CoV is needed and this is generally taken for such products as 10%.   

Extensive testing both static and cyclic on standard profiles with varying fastening patterns have validated the variability values given in 17.1.1A Variability Factors

The factors in 17.1.1A Variability Factors are the same as those found in AS/NZS 1170 and AS/NZS 4600.

C.1.3. RESISTANCE TO CONCENTRATED LOAD

The requirements and general descriptions are taken from AS/NZS 1170.  The method is taken from AS 4040.1

The division of Type 2 is taken from the NZMRM Code of Practice.

C1.3.1.

The residual deformation criterion of L/400 has been set to allow for the use of different metals and plastic for roof and wall cladding. This is a limiting factor because permanent deformation is an indicator of potential stress failure and is also likely to cause ponding and visual distortion.

C.1.3.2.

Because the concentrated load is known and the number of tests is predetermined, it is possible to factorise the test load from 17.1.1A Variability Factors, unlike a UDL test where the test load in unknown and the results are factorised. Multiple concentrated load tests can be carried out on the same sheet provided that there is nil influence of any failure from a previous test.

C.1.4 RESISTANCE TO WIND PRESSURES

AS/NZS 1170.0:2011 defines Serviceability as the Ability of a structure or structural element to perform adequately for normal use under all expected actions

The main function of a roof or wall is to provide a durable weathertight membrane and, therefore, serviceability is the ability to continue to provide a weathertight seal where the fixings penetrate through the cladding under maximum design load. For a Uniformly Distributed Load, this requires finding the applied load under which sufficient permanent deformation occurs that may cause loss of a weather seal at a fixing location. This is regarded as a serviceability failure.

Any buckling from point load that impairs the ability of the profile to be able to carry the same repeated load is also regarded as a serviceability failure.

From these definitions of serviceability for roof and wall cladding serviceability failure is considered the most important performance criterion, rather than Ultimate failure where the roof would blow off or a person would fall through it. Testing of pierce fastened profiled metal roofs has determined that failure under serviceability loads occurs at less than half the load at which strength load failure occurs. Hence serviceability load failure is considered the most important criterion for such roofs.