The NZ Metal Roof and Wall Cladding Code of Practice is a comprehensive design & installation guide, and a recognised related document for Acceptable Solution E2/AS1 of the NZ Building Code.
1. REFERENCE DOCUMENTS
2. TEST METHODS
The ultimate-load test is intended to assess the maximum load at which the cladding and its fastenings would not blow off, or a person would not fall through the roof.
3. SUPPORTING STRUCTURE AND EQUIPMENT
N.B. This is a pressure test from beneath the sheeting to simulate a negative load from above.
For point load testing, a hydraulic cylinder and calibrated load cell is contained within a moveable rigid yoke attached to the main airbox frame, providing universal access to all parts of the supporting structure.
The force measured by the load cell using either a separate digital display or forming part of a computer-based data system must be able to provide an accurate indication of the applied load.
The deflection during the load application must be monitored through a differential displacement transducer and indicator, to enable the recording of the deflection at maximum load, and the residual deflection after load removal.
The structure must not provide any constraint or longitudinal support (e.g., purlin braces) that will prevent membrane action in the cladding under UDL loading.
4. TEST SPECIMEN
A cladding system must consist of sheeting, fastenings and supporting members assembled in a manner identical within those parts of the particular roof or wall of which the test specimen is intended to be a model.
4.2 Width of specimen. The width of a model or the test section of a lapped system must be the width represented by at least two sheet laps. For cladding systems in which the interlocking of the edges of adjoining sheets is essential to their fastening, at least two sheet interlocks must be incorporated in the test specimen.
4.3 Number of spans. For testing the resistance of a roof to concentrated loads, and for testing resistance of continuous cladding to wind pressures, the test specimen must incorporate no fewer than four spans, i.e., two end and two intermediate spans.
4.4. The ratio of the end span to intermediate span must be between 0.6 and 0.7.
5. INTERPRETATION OF RESULTS
5.1 Derivation of design data.
* Refer commentary re statistical reliability
(i) Where the data is taken from tests for a single type, size, and profile of cladding and type and spacing of fastener.
(ii) Where at least three different spans or support spacings have been tested for the same type, size, and profile of cladding and fastener details and that in all three tests the failure mode was the same.
(iii) Where test loads were derived from the same test criteria.
Serviceability limit state failure modes that are classified as different are:
- permanent deformation around the fastener head that would compromise weatherproofness;
- excessive residual deflection from point load or the onset of any de-indexing;
- unclipping; or
- fracture of the cladding or its fixings.
Common strength limit state failure modes which are classified as different include cladding pulling over the fasteners, clips disengaging, de-indexing of sheet interlocks or fasteners pulling from the supporting member.
The Variability factors must be those contained in 17.1.1A Variability Factors and must be applied to both the UDL and point load test results.