Deflection

Deflection is a measured deformation of roof or wall cladding under a load, but there is difference between temporary deflection and permanent deformation.

Temporary deflection of cladding under load is within the elastic limit of the steel; the cladding will regain its original shape and strength properties when the load is removed. Permanent deformation that affects the shape, strength or performance of the cladding is serviceability failure.

With high strength claddings deflection failure is often quite sudden and severe once the point of elasticity is reached, but progressive deflection under repeated loads within the material’s elastic limit is minimal.

Roof design should consider the effect of repeated loads, when expected, because low-strength steel or non-ferrous metals can progressively yield under wind loads or repeated constant foot traffic. Machine roll-curved, crimp curved cladding, and metal roof tiles are usually made from low strength steels.

Deformation Around a Fastener Head

Deformation Around Fastener Head

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Permanent Damage Around Fastener Head

Permanent Damage around Fastener Head

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