Universal Beam and Column Sections (UB and UC) Explained

A universal beam (UB) is a hot-rolled steel I-section with parallel flanges, produced in a standard range of sizes and used for beams in buildings, bridges and industrial structures. Its companion, the universal column (UC), has a wider, squarer profile suited to columns. Between them, they are the workhorses of steel construction in the United Kingdom, Singapore and many other places that grew up with British section tables.

This article explains how UB and UC sections are designated, how their shapes differ and why, the standards they are produced to, and how an engineer selects and checks a section. It is written from the perspective of design practice rather than as a substitute for the published section tables.

What makes a section universal

The term describes a family of rolled I and H sections with parallel inner flange faces, rolled on universal mills that work the web and flanges simultaneously. Parallel flanges make connections simpler than with older tapered-flange joists, because bolts and plates sit flat against the flange.

The section works by putting most of its material in the two flanges, as far from the centre as possible, where it contributes most to bending resistance, and connecting them with a thinner web that carries shear. Our article on the I-beam explains that principle in more detail, and why the shape is so efficient for bending.

Dimensions for UB and UC sections in the British range are given in BS 4-1, while the European standard EN 10365 also lists dimensions for hot-rolled sections including these. Tolerances are covered by EN 10034. The steel itself is normally to EN 10025, in grades such as S275 and S355, as discussed in our article on steel grades in construction.

How UB and UC sections are designated

Sections are described by three numbers: serial depth by serial width, in millimetres, by mass per metre in kilograms, followed by UB or UC. For example:

457 × 191 × 67 UB is a universal beam in the 457 × 191 serial size, weighing about 67 kg per metre.
203 × 203 × 46 UC is a universal column in the 203 × 203 serial size, weighing about 46 kg per metre.

The serial size is nominal. Within one serial size, several sections are rolled using the same rolls but with the rolls set at different spacings, so they have different flange and web thicknesses, different masses and slightly different actual dimensions. The 457 × 191 × 67 UB, for instance, has an actual depth of about 453 mm and a flange width of about 190 mm according to published tables. Heavier sections in the same serial size are slightly deeper and wider.

The practical consequence is that the engineer must use the actual dimensions from the section tables for detailing connections, clearances and fire protection, not the serial size. The mass per metre is also the basis of material cost estimates.

Universal beam versus universal column

The two families have different proportions because they do different jobs.

Universal beams

A UB is deep and relatively narrow, with the depth typically well over the flange width. This gives a large second moment of area about the major axis for the weight of steel, which is what a beam needs to resist bending and limit deflection. The narrow flanges, however, make it less stiff about its minor axis, and a long, unrestrained UB is susceptible to lateral-torsional buckling, where the compression flange buckles sideways and the section twists.

Universal columns

A UC has a depth close to its flange width, giving an H-shape with relatively thick flanges and web. Its minor-axis stiffness is much closer to its major-axis stiffness, which matters for a column that must resist buckling in both directions. UCs are also used as beams where depth is limited, such as transfer beams under low headroom, at the cost of more steel for the same bending capacity.

In international terminology the same distinction appears as I-beams versus H-beams, where wide-flange H sections play the role of UCs.

Selecting a universal beam: the design checks

Choosing a section is an iterative process. A typical sequence for a floor beam is:

Loads and spans. Establish the dead, imposed and other loads, the span and the support conditions, and calculate the design bending moment and shear.
Initial sizing. Pick a trial section from a rule of thumb, such as a span-to-depth ratio, or from the required plastic modulus.
Bending resistance. Check the section’s moment resistance, taking into account section classification (whether the flanges and web are stocky enough to develop full plastic capacity).
Lateral-torsional buckling. Check whether the compression flange is restrained by the floor slab or secondary beams. If it is not, the buckling resistance may govern and a heavier section, or additional restraints, may be needed.
Shear and local effects. Check web shear and, at supports and concentrated loads, web bearing and buckling, adding stiffeners if needed.
Deflection and vibration. Check serviceability deflections and, for floors, the natural frequency and response to footfall. Long-span UBs are often governed by stiffness rather than strength.

In Singapore, steel design is generally carried out to the Eurocodes, with EN 1993 and the Singapore National Annexes setting the rules. Our explainer on Eurocode 3 summarises how that code is organised.

Columns, composite action and alternatives

For a column, the main check is flexural buckling about each axis, which depends on effective length and on the section’s radius of gyration. UCs are efficient here because their minor-axis radius of gyration is relatively large compared with a UB of similar mass. Combined axial load and bending, from eccentric connections or frame action, is then checked using interaction formulae.

Many floor beams act compositely with a concrete slab through shear studs welded to the top flange. Composite action greatly increases stiffness and strength, which means a lighter UB can be used. Other alternatives include fabricated plate girders for very long spans or heavy loads, cellular beams with large web openings for services, and hollow sections, which have advantages for columns and exposed steelwork, as described in our article on hollow structural sections.

Practical considerations on site

Availability matters as much as theory. Not every section in the tables is stocked everywhere, and a design that uses many different sizes increases cost and the risk of errors. Engineers often rationalise sizes across a project, accepting a little extra steel for simpler procurement and fabrication.

Fire protection, corrosion protection and connection design add to the cost of a steel frame and should be considered with section selection. In Singapore’s humid, coastal environment, exposed steel needs an appropriate coating system and detailing that sheds water. In existing buildings, when a UB is to be inserted to replace a removed wall or support new loads, bearing on existing structure, temporary propping and access often govern the choice of section. A structural engineering consultancy can size the beam, design its bearings and specify the propping sequence.

Frequently asked questions

What does 457 x 191 x 67 UB mean?

It is a universal beam with a serial depth of 457 mm, a serial flange width of 191 mm and a mass of about 67 kg per metre. The serial dimensions are nominal; the actual depth and width are given in the section tables and differ slightly.

Is a universal beam the same as an I-beam?

A universal beam is a type of I-beam: a hot-rolled section with parallel flanges in the British standard range. The term I-beam is broader and includes older tapered-flange joists and sections from other standards, such as European IPE or American W shapes.

Can a universal column be used as a beam?

Yes. UCs are sometimes used as beams where depth is restricted, because they carry more load for a given depth. They are less efficient than UBs in pure bending, so they use more steel for the same span and load.

Why do universal beams need lateral restraint?

Without restraint, the compression flange of a long, narrow beam can buckle sideways and the section twists, reducing its capacity well below its full bending strength. Floor slabs, secondary beams or bracing restrain the compression flange and allow the beam to reach its design resistance.

Which steel grade is used for universal beams?

The most common grades are S275 and S355 to EN 10025-2, with S355 increasingly the default because its higher strength often allows lighter sections. The grade must be specified on the drawings and confirmed by mill certificates.

Inserting a steel beam into an existing building, or need a section checked? Talk to our consultancy or get in touch.