Cold-formed and hot-rolled steel
The difference in production
Section titled “The difference in production”Hot-rolled
Section titled “Hot-rolled”The steel is formed while glowing, on a rolling mill. This produces the solid sections: I, H, U, L and hollow sections. Thickness can run to centimetres rather than millimetres.
Cold-formed
Section titled “Cold-formed”Cold sheet drawn from coil is bent gradually into shape by a line of rollers. Thickness is typically between a tenth of a millimetre and a few millimetres.
The difference in behaviour
Section titled “The difference in behaviour”This is the more important one, and everything else follows from it.
What governs
Section titled “What governs”For a hot-rolled section the yield strength governs: it carries what the steel can take.
For a cold-formed section stability enters far earlier: the thin plate elements buckle locally, the lip can rotate, the open section can twist. The cross-section therefore does not work in full. Why thin-walled design differs.
The design standard
Section titled “The design standard”Hot-rolled structures follow EN 1993-1-1; cold-formed ones get supplementary rules from EN 1993-1-3, working with an effective cross-section.
The connection
Section titled “The connection”Hot-rolled work typically uses welding and high-strength bolts. On thin sheet welding is difficult and risky, so self-drilling screws, clinching and rivets dominate — and failure usually occurs in the sheet, not in the fastener.
A thin section heats through much faster, because its surface is large relative to the amount of material. Section factor.
Where cold-formed wins
Section titled “Where cold-formed wins”- Self-weight: far lower, which decides foundations and vertical extensions.
- Accuracy: machine production, members cut to size.
- Freedom of shape: the roll-forming line delivers any length, with several operations, without separate workshop work.
- Erection: dry, fast, no welding.
Where hot-rolled wins
Section titled “Where hot-rolled wins”- Long spans and concentrated loads.
- Simpler design where stability is not the bottleneck.
- Fire: a thick section can be protected with a coating, and that is certified.
Why they are often used together
Section titled “Why they are often used together”Because their strengths complement each other: long-span primary beams in hot-rolled steel, the infill and enclosing structure in LGS. When hot-rolled steel is needed alongside LGS.
The point
Section titled “The point”Not “weaker steel” — the same material with a different geometry. The thinness brings both the advantages and the limits, at the same time.