Modes of Failure

Serviceability limit is a state when a building, or any part of it, becomes unfit for its intended use due to deformation or deflection.

Ultimate limit is a state associated with collapse or failure, or when a building or any part of it becomes unstable or unsafe.

These limit states are not limited to the metal roof and wall cladding, but are intended to be applied to the entire building structure.

Because the prime function of metal roof and wall cladding is to exclude water from the structure, irreversible failure at the serviceability limit state, for example permanent distortion around the fastener head, is generally the governing limit state for pierce fastened roof and wall cladding. This Code of Practice treats serviceability as the criterion of failure for pierce fastened roofs, as these failure levels are far lower than those at which ultimate limit state failure is experienced.

Draft Clause: