Steel and sections

A meter of stud weighs less than a kilo and a half

The default stud of a new CalcSteel project is a C with an 89 mm web and 0.95 mm sheet, weighing 1.38 kg per meter. A 2.80 m stud comes in under 4 kg. Pieces like this put up a two-story house, and the secret is not an exotic steel: it is the combination of three things that this page opens one by one.

The first is the steel, with a known strength guaranteed by the product standard. The second is the shape: bends and lips give stiffness to a sheet that, flat, would be a leaf. The third is the protection: the zinc that lets the thin sheet last as long as the house.

The standards showed which standard each check comes from. Here the subject is the material that reaches the site: what is written in the section name, which number the engine uses for it, and why the same wall can have different sections in Brazil and in Australia.

• 230 MPa: minimum yield of the ZAR steel used for LSF in Brazil
• 0.95 mm: the most common wall thickness
• 6 m: the commercial bar length the app uses in Brazil
• 600 mm: default stud spacing in BR, AU and NZ

Two numbers define the steel: fy and fu

Pull a strip of steel and it stretches in proportion to the force, up to a point where it starts to yield: it stretches without the force rising. The stress at that point is the yield strength, fy. Keep pulling and, after yielding, the steel still gains some strength until it breaks; the highest stress reached is the tensile strength, fu. The first number tells when the piece no longer returns to what it was; the second, when it breaks apart.

Where each number comes in

Almost every member check starts from fy: stud compression, header bending, buckling. fu appears where the piece can break without yielding first: in the net section under tension and in connections, where the sheet is torn or crushed by the screw. The fu/fy ratio shows how much the steel still holds after it yields.

The steel of Brazilian LSF is ZAR, high-strength zinc-coated sheet, and the number after the letters is fy in MPa. The market practice recorded by CBCA (the Brazilian Steel Construction Center) is not to go below 230 MPa, ZAR 230.

Values in MPa, from the engine's materials catalog. The wizard shows each steel as "ZAR-230: fy 230 / fu 310 MPa".

Each market has its steel, and the project starts with it

The steel is not a loose choice: it comes with the country. When you create an LSF project, its market sets the list of steels on offer and the one already selected. In Brazil, the four ZAR grades, with ZAR-230 selected. In Australia and New Zealand, the two AS 1397 steels, with G300 selected and G550 on the list. In the USA, the ASTM steels, with A1003 selected.

G300 and G550, the AS 1397 steels

The "G" stands for grade and the number is the minimum fy in MPa. G550 is a cold-rolled high-strength steel: the BlueScope data sheet for TRUECORE, an LSF steel sold in Australia, guarantees a minimum yield of 550 MPa, with an AZ150 coating.

In the app catalog G550 has fu equal to fy, that is, almost no reserve after yielding. That is why AS/NZS 4600 gives these steels their own rule, in clause 1.5.1, and the engine applies the standard of the project's market.

Markets without their own steel

Not every country has its own row in the markets catalog. When it is missing, the project starts from the Brazil definition, with its default steel. You change the steel later, in the Structure tab, if the project calls for another.

When the country has its own row but leaves one key blank, only that key comes from Brazil. That is the case of the commercial bar length in Australia, New Zealand and the USA, shown in Commercial bar and spacing by market.

1. Where to see and change the steel

In the project wizard, Structure tab, the Steel block lists the market's steels with fy and fu in MPa. The selected one is the market default.

2. Change it only for a reason

A grade above ZAR-230 is only worth it if the section supplier guarantees it in writing. The engine designs with the fy you chose, not with what arrived on site.

3. Check it against the supplier

In the app's materials catalog, each steel carries the name and standard of the product, such as "ZAR-230 (NBR 6355)" or "G550 AZ150 (AS 1397)". That is what the engineer checks against the mill certificate and the invoice for the sections.

The sheet is thin because the zinc protects it

A sheet under one millimeter has no thickness to lose to rust. What makes it last is the metallic coating applied at the mill, by hot dipping, on both faces of the coil before it becomes a section. Zinc keeps air and moisture away from the steel and, where the coating is scratched, corrodes in place of the steel.

How to read the coating class

The class gives the coating mass per m² of sheet, both faces added. In Z275, the Z stands for zinc and 275 is grams per m²: about 137 g per face, close to 19 µm of zinc on each side. In AZ150, the coating is an aluminum and zinc alloy, 150 g/m² on both faces.

In Brazil, CBCA records a minimum of 180 g/m² of zinc under the NBR, and 275 or 350 g/m² under SINAT guideline no. 003, depending on how aggressive the environment is.

0.95 in the name, 0.914 in the calculation

Zinc protects, but it carries nothing. That is why NBR 14762 (clause 3.1.12) defines the design thickness as that of the steel sheet without the coating. NBR 15253 sets how much to deduct: 0.036 mm, both faces added. The CBCA Steel Framing engineering manual works it out for the most common section: 0.95 minus 0.036 gives 0.914 mm.

This is the CBCA manual's convention, which the engine follows: the outer dimension loses the coating of both faces and the centerline stays where it was. Area, inertia and strength come from the design section; the self-weight comes from the catalog, with the zinc, because zinc has weight.

Machine catalogs: already base steel

The FRAMECAD and Howick sections and the American SSMA catalog record the base steel thickness, without coating. The 0.95 of the FRAMECAD C is already 0.95 mm of steel, and the engine deducts nothing from it. The catalog states this section by section, and that is the data the engine decides by.

Why so thin

Strength comes from fy and from the shape: the web keeps the flanges apart, the lips hold the flange edges. Thickening the sheet costs steel along the whole length. CBCA records 0.80, 0.95 and 1.25 mm as the usual thicknesses: 0.95 in walls, 1.25 in beams and columns.

A section does not know what it is; the role tells it

The same C can be a stud, a track or a truss chord. What changes is the role of the piece in the structure, and the app picks the section, the deflection limit and the check by role. The table uses the names of the Structure tab and, for those who work with overseas suppliers, the terms each market's catalog records.

Market terms as each country's catalog records them; an empty cell is a role with no term of its own recorded. Each piece of the wall in detail in Anatomy of a wall.

The sections a new project starts with

A new LSF project starts roll-formed, on the FRAMECAD F325iT roll former. The sections for each role come in two layers: first those of the project's market, then, on top, those the machine defines. Roles the machine does not form, such as the strap, the hat-section purlin and the floor, keep the market's section.

One C, four thicknesses

The roll former forms a fixed section: the F325iT makes the C with an 89 mm web and a 12 mm lip. What varies is the coil fed in, and with it the thickness. The app catalog has four, from 0.55 to 1.15 mm, and the machine accepts sheet from 0.55 to 1.2 mm. In a roll-formed project, the section picker for the roles the machine makes lists only these four.

Flanges of 41 and 39

The two flanges are not the same width. With one 2 mm narrower than the other, one C fits inside the other: F325iT literature calls the section boxable. That is what lets two pieces close into a box with the same section.

One section for everything simplifies the factory: every C piece comes off the same machine profile, and only the coil changes thickness.

From coil to finished piece, with holes and cuts

The roll former takes the strip from the coil, punches and notches the sheet while it is still flat, bends the strip little by little through rollers until it becomes a C, and cuts it to length. Each piece comes out with a name, a length and the operations at the points the design called for. That is why the machine file is part of the design: what is not in it is not made.

Shape letter, dimensions in mm, thickness at the end

The section name in the app follows the logic of cold-formed section designations: first the letter for the shape of the section, then the outer dimensions in millimeters, from largest to smallest, and finally the thickness. The thickness uses a decimal point, as in the catalog.

The bar length and the distance between studs

Two market numbers change the wall without changing the standard. The maximum bar is the longest length of section that can be bought or formed in one piece: a track longer than that is spliced. The spacing is the distance between stud centerlines, which usually matches the width of the sheathing board so that every joint falls on a stud.

Dimensions in mm, from the app's markets catalog as of 22 Oct 2026, for track and stud. * Value inherited from the Brazil definition. In the USA, the three spacings are 12, 16 and 24 inches.

Where the spacings come from

In Brazil, 400 and 600 mm are the local practice, with 600 selected. In Australia, the TRUECORE data sheet limits spacing to 600 mm. In the USA, the spacings are those of construction in inches.

Spacing is the first number you adjust when the stud does not pass: a smaller spacing shares the wall load among more studs.

1. Where to adjust

Structure tab of the wizard: Stud spacing (200 to 1,200 mm, with the market's usual values in the hint) and Maximum bar (1,000 to 12,000 mm). The bar applies to track and stud.

Three ways a thin section gives way before it yields

The standards showed the three modes on the cross-section. Here they appear along the member, because the most useful difference between them is the wavelength: the shape the section takes as it gives way repeats over short, medium or full-length stretches, and that tells you what restrains each one.

Local

One plate of the section, usually the web, wrinkles between the bends. The member does not fail: the bent edges keep carrying load and the wrinkled middle stops counting. The standard handles this through the effective width, which removes from the area the part that does not work.

Distortional

The flange and lip together rotate about the bend with the web, and the section changes shape. It is the typical mode of lipped sections: too short, the lip does not hold the flange. It depends on the proportions of the section, not on the member length.

Global

The whole member moves without the section changing shape: flexure, torsion or both. It depends on the length between braced points, and that is what blocking, strap and screwed sheathing shorten.

Where each mode enters the check

The engine checks all three modes on every cold-formed section, under the NBR 14762 clauses for a Brazilian project. The member strength is the lowest among the modes checked. The calculation, with the numbers of a real stud, is in the Design pages, in Studs; here is the map.

What the designer controls

• Local: the thickness; a thicker sheet wrinkles later
• Distortional: the section and the lip; the mode is about proportions
• Global: the bracing; blocking, strap and board shorten the wave
• Global: the spacing; less load per stud

Why strong steel is not enough

In all three modes, the critical load depends on the modulus E and on the geometry, and E is the same for every LSF steel in the app. A higher fy only pays off if the member gets close to yielding before it gives way. In a slender stud, instability governs, and swapping ZAR-230 for ZAR-345 changes little.

The section, in one line

Steel with guaranteed fy (ZAR, G300, G550, A1003) → zinc on both faces, left out of the calculation → sheet bent into a C for shape, not thickness → a role in the structure → a name that gives shape, dimensions and thickness → three instability modes, checked under the market's standard.

Five ideas to keep

• fy governs the member; fu, the hole and the connection
• Zinc protects and carries nothing: 0.95 becomes 0.914
• Machine catalogs already record the base steel
• The role picks the section, and the machine goes on top of the market
• In a slender stud, instability matters more than the steel

The house so far

• ZAR-230: default steel in Brazil
• C 89: x41/39x12x0.95, the stud
• 600 mm: stud spacing
• 6 m: commercial bar