Last reviewed 16 Sept 2026 · 5 min read
What cold-formed steel is
Cold-formed steel (CFS) members are shaped at room temperature from thin steel sheet or strip, typically 0.4 mm to about 6 mm thick, by:
- roll forming — the strip passes through successive pairs of rolls (continuous production of long sections), or
- press braking — bending sheets in a press (short runs, custom shapes).
Also called light-gauge steel. Hot-rolled sections, by contrast, are shaped at high temperature from thick billets.
Common shapes and uses
| Section | Typical use |
|---|---|
| C (lipped channel) and Z sections | Purlins, side girts, studs, joists |
| Sigma, hat (omega) sections | Purlins, furring, deck supports |
| Profiled roof/wall sheeting | Cladding, roofing |
| Composite floor decking | Steel deck acting with concrete slab |
| Hollow sections (tubes) | Light trusses, frames, scaffolding |
| Light steel framing (LSF) | Walls, floors and roofs of low-rise houses, modular units |
| Storage racks, transmission towers (light), automobile and railway coach bodies | Industrial |
Pre-engineered buildings commonly combine hot-rolled/built-up main frames with cold-formed Z and C purlins and girts.
Advantages
- Very light — high strength-to-weight ratio; easy transport and erection.
- Shapes can be optimised for the job (lips, intermediate stiffeners).
- Cold working raises the yield strength at corners (strain hardening).
- Mass production with close tolerances; fast, dry construction.
- Non-combustible, termite-proof, recyclable.
- Sections can nest for compact transport.
Disadvantages
- Thin elements are prone to local buckling and distortional buckling.
- Low torsional stiffness of open sections (C and Z) — shear centre away from the web leads to twisting.
- Sensitive to corrosion (little thickness to lose) — needs galvanising or coatings.
- Reduced ductility at corners; limited fire resistance without protection.
- Connections need special fasteners.
Design code
IS 801 — Code of practice for use of cold-formed light gauge steel structural members in general building construction (Indian code). Internationally: AISI S100, EN 1993-1-3, AS/NZS 4600. Modern design uses the effective width method or the direct strength method (DSM).
Local buckling and effective width
A thin flat plate in compression buckles at a stress
where depends on edge support: about 4.0 for a stiffened element (both longitudinal edges supported by webs or adequate lips) and about 0.43 for an unstiffened element (one edge free, e.g. a flange without a lip).
Unlike columns, plates carry load after buckling (post-buckling strength): stress redistributes towards the supported edges. The effective width concept replaces the non-uniform stress by the maximum edge stress acting on a reduced width :
= maximum compressive stress in the element. The section properties (, , ) are computed using effective widths of the compression elements.
This is why lips (edge stiffeners) and intermediate stiffeners (grooves in wide flanges and webs) are so effective: they convert unstiffened elements into stiffened ones, raising from 0.43 to about 4.
- Stiffened element — flat element with both longitudinal edges connected to other elements (web or lip).
- Unstiffened element — flat element with one longitudinal edge free.
- Edge stiffener — a lip along the free edge.
- Flat width-to-thickness ratio — the design code sets maximum permissible values separately for unstiffened elements, lip-stiffened elements, fully stiffened elements and webs; beyond these, elements are too flexible to be used.