What is a U-channel?
A U-channel, also called a channel section or U-beam, is a steel beam with a U-shaped cross-section: a vertical web with two flanges that point to one side only. Because the flanges face one way, the back of the section is flat, which makes it easy to fix against a wall, another steel section or a timber joist.
UPN and UPE
In European hot-rolled steel you will mainly come across two families:
- UPN: the inner faces of the flanges are tapered. This is the classic channel.
- UPE: the flanges are parallel, which makes bolted connections simpler because you do not need tapered washers.
The number after the name is the depth in millimetres, so a UPN 160 is 160 mm deep. Dimensions and masses are given in EN 10365, tolerances in EN 10279. In the UK, parallel flange channels are also sold as PFC. Cold-formed U and C sections, pressed from thin sheet, are much lighter alternatives.
Application
- Trimmer beams around floor openings and stairwells.
- Lintels over openings, often two channels back to back or combined with a plate.
- Stringers for steel staircases.
- Facade rails and posts in steel-framed buildings and sheds.
- Strengthening timber joists by bolting a channel to the side.
Points to watch
- Twisting and buckling: because the web is off-centre, the shear centre lies outside the section. A channel loaded through its web tends to twist. Provide lateral restraint or have a structural engineer check it.
- No swaps by eye: a channel of the same depth is usually less stiff than an I- or H-section. Never replace a calculated section without checking.
- Corrosion: galvanise or coat well outdoors, and avoid water collecting inside a channel laid with its opening upwards.
- Fire: load-bearing steel in homes may need fire-resistant boarding or coating.
Related terms
- Structural steel sections
- H-beam
- IPE beam
- Cold-formed steel
- Lintel
- Stair stringer
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