Two Types of C Channel
A hot rolled channel is produced as a single rolled section with a constant thickness, a defined root radius and either tapered inner flange faces, designated UPN, or parallel flange faces, designated UPE. A cold formed C section is made by bending a strip of steel and is normally thinner, lighter and produced to a specified width and depth for a particular framing system. Both are described as C channel or U channel in trade. The distinction matters because their section properties, tolerances and connection behaviour differ, and the two cannot be used interchangeably without checking the section data.
Dimensions and Section Data
Hot rolled channels follow EN 10365 in European practice and GB/T 706 in Chinese practice, with depths from 50 mm to 400 mm. Cold formed C sections are made to order, commonly with depths from 80 mm to 300 mm, flange widths from 40 mm to 100 mm and thicknesses from 1.5 mm to 6 mm.
| Type | Typical Depth mm | Typical Thickness mm | Principal Use |
| Hot rolled UPE or UPN | 80 to 400 | 5 to 15 | Structural edge beams and supports |
| Cold formed C section | 80 to 300 | 1.5 to 6 | Purlins, girts and light framing |
The lip or return at the flange edge of a cold formed section stiffens the flange and improves its local buckling resistance, which is why cold formed channels perform better than their thin gauge might suggest.
Grades and Standards
Hot rolled channels are supplied in S235JR, S275JR and S355JR under EN 10025-2, in Q235B and Q345B under the Chinese standards, and in SS400 under JIS G 3101. Cold formed sections are produced from strip in Q235, S250GD or S350GD with a zinc coating, and the dimensional and tolerance requirements are covered by general cold formed section standards such as EN 10162. Where the channel will be galvanized after fabrication, the steel must be suitable for the process and the design must include vent and drain holes so that the coating can reach internal surfaces and no air is trapped during dipping.
Design and Connection Notes
A channel is strong in bending about its major axis but weak in torsion and in bending about the minor axis, because the shear centre lies outside the section. Loads applied away from the shear centre therefore produce twisting as well as bending, and this must be considered when the channel is used alone. Back to back or boxed channel arrangements restore symmetry and greatly improve torsional behaviour. Connections are usually made to the web because the web provides a flat surface for a cleat or an end plate, and the bolt group should be kept clear of the root radius.
Typical Applications
Roof purlins and wall girts.
Edge beams and floor trim.
Equipment and machine support frames.
Racking uprights and shelving.
Vehicle chassis and trailer frames.
Frequently Asked Questions
Q: What is the difference between UPE and UPN channels?
UPE channels have parallel flanges that provide a flat surface for bolts and fittings, while UPN channels have tapered inner flange faces and are the traditional European profile.
Q: When is a cold formed C section used?
Cold formed C sections are used for purlins, girts and light framing because they are light, economical and can be produced to the exact size required for a system.
Q: Why do channels twist under load?
The shear centre of a channel lies outside the section, so a load applied through the web or the flange produces a torsional moment that twists the member.
Q: How can twisting be prevented?
Use back to back or boxed channels, provide lateral restraint along the length, or design the connection so that the load is applied close to the shear centre.
Q: Can C channels be galvanized?
Yes. Provide vent and drain holes so that molten zinc can reach all surfaces and trapped air cannot prevent complete coating.