Yield strength and thickness go together
Why one figure is not enough
Section titled “Why one figure is not enough”You often hear “this is a one-millimetre profile” or “this is stronger steel”. Neither statement says anything about capacity.
The capacity of a thin-walled section is four things together:
- thickness,
- steel grade (yield strength),
- section geometry — depth, flange width, whether there is a lip and how big,
- restraint conditions — over what length and in what way the member is braced.
What thickness drives
Section titled “What thickness drives”Stability
Section titled “Stability”A thinner plate element buckles sooner. Increasing thickness therefore does not just add material, it improves utilisation proportionally as well.
Connection capacity
Section titled “Connection capacity”In a screwed connection the behaviour of the sheet governs: thinner sheet tears or pulls out around the screw sooner. A thicker section often improves the connection more than the member.
Screwability
Section titled “Screwability”A self-drilling screw has a thickness range in which it works reliably.
What yield strength drives
Section titled “What yield strength drives”The limit of the material — but it can only come into play if the cross-section gets that far. On a slender section, stability governs earlier and the higher yield strength is not fully used.
The practical consequence
Section titled “The practical consequence”The designer designs the thickness too
Section titled “The designer designs the thickness too”Not one thickness for the whole building, but member by member. Thicker where the load is high, thinner where it is not. This is the single biggest saving available on the structure.
Production has to follow, which is what machine thickness tracking makes possible. Auto-gauging.
Marking is a structural matter
Section titled “Marking is a structural matter”If the building contains sections of different thickness that look identical, part marking is not administration: a swapped member breaks the assumption behind the design.
Substitution is not simple
Section titled “Substitution is not simple”“The same, only thinner” does not exist. A thinner section works with a different effective cross-section, so it is a different structure.
The point
Section titled “The point”Thickness and steel grade only mean something together with geometry and restraint. That is why you cannot identify from a catalogue what a profile carries.