Structural steel sections explained: beams, channels and how to choose

Structural steel sections are the standard hot-rolled shapes that frame buildings and machines: I-beams (IPE), wide-flange H-beams (HEA and HEB), channels (UPN and UPE), angles, tees and hollow sections, in grades S235, S275 and S355. Each shape puts steel where it resists load best, so the right section carries more for less weight. The beam shapes span and support, channels and angles frame and brace, and hollow sections give even strength in every direction. This guide explains the family and how to choose between them.

What structural sections are

A structural section is a length of steel hot-rolled into a shape that carries load efficiently. Instead of a solid bar, the metal is arranged into an I, an H, a U or an L so that it resists bending and buckling with the least material, which makes steel frames both strong and economical. The shapes are standardised across Europe for their dimensions and tolerances, so sections from any mill fit and combine predictably. They are the building blocks of steelwork, and choosing the right one for each member is the heart of structural design.

I-beams: IPE

The IPE section is the classic I-beam, with a tall, relatively narrow profile and tapering or parallel flanges. Its depth is much greater than its width, which makes it very efficient at resisting bending about its strong axis, so it is the natural choice for beams that span and carry vertical load, such as floor and roof beams and lintels. Because most of its strength is in one direction, an IPE is used where the load is predictable and mainly vertical. Its dimensions follow EN 10365, which replaced the older DIN tables.

Wide-flange H-beams: HEA, HEB and HEM

The HE sections are wide-flange beams, as wide as they are deep, which gives them strength in both directions and makes them stable as columns. HEA is the lighter series, HEB the standard heavier series and HEM the extra-heavy series, so the same nominal size comes in three weights. Their square proportions suit columns and posts that carry load from any direction, as well as heavily loaded beams. Where an IPE would be efficient as a simple beam, an HE section is chosen for a column or where width and two-way strength are needed.

IPE or HE: choosing a beam

The choice between an IPE and an HE section comes down to how the member is loaded. For a beam spanning between supports and carrying mainly vertical load, the deep, narrow IPE gives the most strength for the weight. For a column, or a beam that also has to resist sideways load or buckling, the wide, square HE section is more stable. As a rule, IPE for beams and HE for columns is a good starting point, refined by calculation. Our guide to black steel structural sections gives the full detail on beams and channels.

Channels: UPN and UPE

Channel sections have a U-shaped profile, with a web and two flanges on the same side, giving a flat back that sits neatly against other members. UPN is the traditional channel with tapered flanges, and UPE the parallel-flange series that is easier to bolt and connect. Channels are used for frames, purlins, edge beams, trims and members that must fix flat against a surface. Their tolerances follow EN 10279. Where a symmetrical beam is not needed and a flat fixing face is useful, a channel is often the practical choice.

Angles and tees

Angle and tee sections handle bracing, framing and connection. Angle, the L-section, comes in equal and unequal leg forms and is used for bracing, brackets, frames and supports, with its own standard EN 10056; our guide to steel angle covers it in full. Tee sections, T-shaped in profile, suit framing and connections where a stem and a flat face are wanted, and are used as made or split from beams. Both are smaller supporting members rather than main spans, and both are valued for the flat faces they present for fixing.

Hollow sections

Hollow sections put the steel in a closed tube, square, rectangular or round, which gives even strength in every direction and a clean, closed look. This makes them efficient for columns, exposed structures, frames and anything loaded in more than one direction or subject to twisting. They also have no sharp internal corners to trap dirt, which suits architectural and hygienic work. Cold-formed hollow sections follow EN 10219, covered in our guide to EN 10219 hollow sections. Where an open section would twist or look unfinished, a hollow section is the answer.

The web and the flanges

Most sections share the same anatomy of a web and flanges, and understanding it explains why the shapes work. The flanges are the wide horizontal parts at the top and bottom, and they do most of the work of resisting bending, because they sit furthest from the centre where the stress is highest. The web is the vertical part joining them, and it mainly carries shear and holds the flanges apart. A deep section with the flanges far apart resists bending well, which is why beams are deep, and it is this simple geometry that lets a shaped section outperform a solid bar of the same weight.

Connecting structural sections

Sections are joined into frames by bolting or welding, and the shape affects how. Open sections such as beams, channels and angles give easy access to their faces, so they are readily bolted through cleats, end plates and gussets, or welded directly, which is why they dominate bolted steel frames. Hollow sections give a clean look but only outside access, so they are usually welded or joined with special fittings. Base plates, cleats and stiffeners are fabricated from plate and angle to transfer load into and between members. Designing the connections is as much a part of steelwork as choosing the sections themselves.

Grades and standards

Structural sections are rolled in the grades of EN 10025-2, defined by minimum yield strength: S235 at 235 megapascals, S275 at 275 and S355 at 355, with quality suffixes JR, J0 and J2 for impact toughness. Dimensions and tolerances are set by section standards: EN 10365 for the dimensions of I, H and U sections, EN 10034 for the tolerances of I and H sections, EN 10279 for channels and EN 10056 for angles. Ordering to the grade and the standard gives a defined, repeatable section. Our guide to structural steel S235, S275 and S355 covers the grades.

Choosing the right section

This is a starting point rather than a rule, because the final section is sized by structural calculation to the relevant Eurocode for the loads and spans involved. Matching the shape to the role first, then sizing it, gives an efficient, economical frame.

Protecting structural steel

Structural sections are supplied as bare, black hot-rolled steel, which rusts if left exposed, so protection is planned with the design. Indoors and in dry conditions bare or painted steel is fine. Outdoors, hot-dip galvanising gives durable protection, and paint systems or a duplex of galvanising plus paint are used for the longest life or a specific colour. Our guide to galvanised steel covers the options. The protection is chosen for the exposure, so the frame lasts as long as it needs to.

Structural steel sections from ULAMEX

ULAMEX has supplied structural steel sections since 1988, in the shapes and grades that engineers and fabricators specify.

Need structural sections for a project? Tell ULAMEX the sections, the grade and the quantity and the desk will confirm availability and return a non-binding quotation. See our guides to black steel structural sections and EN 10219 hollow sections, and our supply capabilities, or contact the export desk at [email protected] or +48 504 424 761.

Frequently asked questions