A steel channel is a section with a U-shaped cross-section, made up of a web and two flanges on the same side of it. It is widely used for built-up columns, roof purlins, chassis and steel frames. This guide covers channel types, the parts of the section, the UNP channel size and weight chart, steel grades and applications.
What is a steel channel and what are its parts?
A channel has three parts: the web, the vertical plate of the section, and two flanges at the top and bottom, both on the same side of the web. This gives a section shaped like the letter U or C. The flat back of a channel provides a convenient surface for connecting to other members, walls or plates, which is what sets it apart from an I-beam.
Like an I-beam, a channel resists bending about its strong axis well, but because the section has only one axis of symmetry, its behaviour in torsion is different.
Types of steel channel
Hot-rolled versus press-formed channel
| Property | Hot-rolled channel | Press-formed channel (bent from sheet) |
|---|---|---|
| Process | Hot rolling of a steel billet | Slitting sheet and cold bending |
| Web and flange thickness | Different; flanges thicker than the web | Uniform, equal to the sheet thickness |
| Outer corners | Sharp, square | Rounded |
| Dimensions | According to the standard table | Can be made to custom sizes |
| Typical use | Structural, load-bearing members | Light fabrication, frames, tracks and trims |
Designation and section dimensions
The size number of a channel is the nominal depth of the section in millimetres. For example, UNP 140 has a depth of 140 mm.
UNP channel size and weight chart
| Size | Depth h (mm) | Flange width b (mm) | Web tw (mm) | Flange tf (mm) | Mass per metre (kg) | Mass of a 6 m length (kg) | Mass of a 12 m length (kg) |
|---|---|---|---|---|---|---|---|
| UNP 50 | 50 | 38 | 5.0 | 7.0 | 5.59 | 33.5 | 67.1 |
| UNP 65 | 65 | 42 | 5.5 | 7.5 | 7.09 | 42.5 | 85.1 |
| UNP 80 | 80 | 45 | 6.0 | 8.0 | 8.64 | 51.8 | 103.7 |
| UNP 100 | 100 | 50 | 6.0 | 8.5 | 10.6 | 63.6 | 127.2 |
| UNP 120 | 120 | 55 | 7.0 | 9.0 | 13.4 | 80.4 | 160.8 |
| UNP 140 | 140 | 60 | 7.0 | 10.0 | 16.0 | 96.0 | 192.0 |
| UNP 160 | 160 | 65 | 7.5 | 10.5 | 18.8 | 112.8 | 225.6 |
| UNP 180 | 180 | 70 | 8.0 | 11.0 | 22.0 | 132.0 | 264.0 |
| UNP 200 | 200 | 75 | 8.5 | 11.5 | 25.3 | 151.8 | 303.6 |
| UNP 220 | 220 | 80 | 9.0 | 12.5 | 29.4 | 176.4 | 352.8 |
| UNP 240 | 240 | 85 | 9.5 | 13.0 | 33.2 | 199.2 | 398.4 |
| UNP 260 | 260 | 90 | 10.0 | 14.0 | 37.9 | 227.4 | 454.8 |
| UNP 280 | 280 | 95 | 10.0 | 15.0 | 41.8 | 250.8 | 501.6 |
| UNP 300 | 300 | 100 | 10.0 | 16.0 | 46.2 | 277.2 | 554.4 |
Nominal dimensions and masses according to EN 10365. Actual mass may vary within the tolerance permitted by the standard.
Theoretical mass based on a density of 7850 kg/m³; actual mass may differ slightly within the tolerance of the standard.
Calculating channel weight
The mass of a length of channel is the mass per metre (from the table) multiplied by the length. For example, UNP 120 at 13.4 kg per metre weighs about 80.4 kg for a 6 m length and about 160.8 kg for a 12 m length.
Steel grades for channels
Structural channels are normally made from non-alloy structural steels. The common grades according to EN 10025-2 are:
| Grade (EN 10025-2) | Former DIN name | Min. yield strength (MPa) | Tensile strength (MPa) |
|---|---|---|---|
| S235JR | St37-2 | 235 | 360 – 510 |
| S275JR | St44-2 | 275 | 410 – 560 |
| S355JR | St52-3 | 355 | 470 – 630 |
Values apply to nominal thicknesses up to 16 mm.
How channels are made
Hot-rolled channels are produced by hot rolling. A steel billet is reheated to rolling temperature and passed repeatedly through rolling stands, gradually taking the U shape. The product then cools on a cooling bed, is straightened and is cut to standard length. Press-formed channels are made by slitting sheet and bending it cold with a press brake or rolls.
Applications of steel channels
- Built-up columns and beams: two channels joined by batten plates or plates form a double column or beam.
- Purlins and roof members: roof purlins of industrial buildings and truss members.
- Stairs: the stringers of steel staircases.
- Lintels and frames: beams over openings and frames for large doors.
- Bracing: bracing members in steel frames.
- Chassis and machinery: truck and trailer chassis, equipment structures and conveyors.
Design note: the shear centre of a channel lies outside the section, behind the web. If the load does not pass through this point, the member twists as well as bends. A single channel therefore needs adequate lateral restraint or should be used as a double section.
Storage notes
- Stack lengths on level supports, clear of the ground, to prevent bending and contact with moisture.
- Preferably stack channels so that water cannot collect inside the U shape.
- Before use, check straightness, section dimensions and the absence of twist.
Frequently asked questions about steel channels
What is the difference between a channel and an I-beam?
In an I-beam the flanges extend on both sides of the web, giving an I shape, while in a channel both flanges are on one side of the web, giving a U shape. A channel has a flat back for connections.
What does the size number of a channel mean?
It is the nominal depth of the section. For example, UNP 140 has a depth of 140 mm.
What is the difference between UNP and UPE channels?
In a UNP the inner flange faces are tapered, while in a UPE the flanges are parallel with constant thickness. UPE is usually lighter and easier to bolt through the flange.
How is the weight of a channel calculated?
Read the mass per metre from the standard table and multiply by the length. For example, UNP 100 at 10.6 kg per metre weighs about 63.6 kg for a 6 m length.
What is a double channel?
Two channels joined back to back or toe to toe to obtain a symmetrical, stronger section for a column or beam.
Related steel sections
RebarI-beamSheetProfilePipeAngle bar
References and standards
- EN 10365: Hot rolled steel channels, I and H sections, dimensions and masses
- DIN 1026-1 and DIN 1026-2: Dimensions of tapered-flange (UPN) and parallel-flange (UPE) channels
- EN 10279: Hot rolled steel channels, tolerances on shape, dimensions and mass
- EN 10025-2: Hot rolled products of non-alloy structural steels, technical delivery conditions
- Iranian National Building Regulations, Part 10: Design and construction of steel buildings
