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Fatigue

The performance of metal roof and wall cladding is affected by stress as all metals may be subjected to fatigue under repeated heavy load conditions.

Metal cladding can fail at a much lower point than the yield stress when there is movement under continued fluctuating stress. A cyclic load test is used to determine the performance of cladding under load reversal.

All metal joints will suffer stress because of movement caused by expansion, vibration, traffic or wind. A sealed joint should have enough fasteners to mechanically resist this stress, because sealant or solder alone do not offer enough resistance. Load spreading washers are used in areas subjected to high wind design loads to give greater resistance to any stress-cracking at fixing holes.

High-strength steel is subject to fatigue, which seldom happens in practice. Other metals, such as lead and copper, are restricted in length or the overall panel size to avoid cracking by fatigue. Sharply folded corners should be avoided on these materials and the minimum radii requirements should be followed.

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