"RSJ" - rolled steel joist - is the name most people use for any steel beam. Strictly, an RSJ is an older section shape with tapered flanges. Almost all modern structural beams in the UK are universal beams (UB) with parallel flanges, rolled to a standard range of sizes. When your engineer specifies a beam, it will almost certainly be a UB, UC or PFC.
The common steel sections
- UB - universal beam: deeper than it is wide; the workhorse for spanning openings and floors.
- UC - universal column: roughly as wide as it is deep; used for posts and columns, and sometimes for beams where depth is limited.
- PFC - parallel flange channel: a C-shaped section, often used in pairs, as trimmers, or where one flat face is needed.
- RSA - rolled steel angle: L-shaped; used for lintels, brackets and secondary steel.
- SHS / RHS / CHS - hollow sections: square, rectangular or circular tubes; popular for posts, frames and exposed architectural steel.
Reading a section size
A designation such as UB 203x133x25 tells you three things: the nominal depth (203 mm), the nominal flange width (133 mm) and the mass (about 25 kg per metre). So a 4 m length of UB 203x133x25 weighs about 100 kg. The engineer may also state the steel grade - typically S275 or S355 - which describes its strength.
Why the exact section matters
Two beams of the same depth can have very different strengths and weights. Never substitute a "similar" beam without the engineer's approval - the calculations depend on the exact section and grade. If a section is hard to source, a fabricator can suggest alternatives for the engineer to check.
What to send when you order
- The engineer's calculations and any structural drawings
- Lengths, bearing details and connection requirements
- Whether you need end plates, bolt holes, splices or baseplates
- Coating requirements and where the steel will be located