Material Grade
To test for tensile strength the material is subjected to a longitudinal (stretching) load, and values are taken for yield strength (when it permanently deforms) and tensile strength (when it breaks). Elongation is also measured during this test.
The minimum tensile strength defines the grade of steel, eg, G550 for high-strength light gauge steel, but to comply with this grade the yield strength and elongation must also fall within defined parameters.
Yield strength is an important determinant of the strength of a profile, along with profile shape and material thickness. High tensile material will have more resistance to failure such as buckling around the fastener under wind uplift, pull-through of the fastener head, or buckling under foot traffic load. However, tensile strength has a negligible effect on deflection under load.
Where 0.55 material is specified for straight corrugate or trapezoidal roofing, it is unacceptable to substitute G300 for G550 grade material as the resultant profile will have little strength advantage over 0.40 mm G550.
Aluminium is defined by a hardness grade ranging from H32 to H38. Typically, H34 is used for flashings, severe profiles such as trough sections, and profiles that are to be curved. Most corrugated and Trapezoidal profiles are manufactured using H36.
It must be remembered that the alloy also affects strength. H36 aluminium in 5005 or 5025 alloys, which are typically used in New Zealand, will have considerably greater tensile strength than the same grade in a 3000-series alloy.
End Use for Typical Alloys
| Material | Grade | Typical End Use |
|---|---|---|
| Steel | G300 | Flashings, ridging, spouting, curving, some trough sections. |
| G550 | Corrugated and trapezoidal profiles, some trough sections. | |
| Aluminium 5505/5025 | H32 | Lock seaming |
| H34 | Flashings, curved roofing, trough sections, and tray roofing. | |
| H 36 | Flashings and profiled roofing, trapezoidal sections, and corrugate. |
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