Hollow Sections, PFC Channels and Unusual Profiles: When to Choose Alternatives to a Standard UB Beam

When most people think of structural steel, they picture a standard Universal Beam (UB). And for good reason. UBs are versatile, widely available, and suitable for many domestic and commercial projects.

But they are not the only option.

Depending on the layout, loading conditions, connection details, and architectural requirements, a hollow section, PFC channel, or other profile may actually be the smarter choice. Understanding when to move beyond a standard UB can save weight, simplify connections, and improve overall performance.

Here’s what you need to know.

When a Universal Beam Isn’t Ideal

Universal Beams are excellent for spanning openings and carrying vertical loads. Their I-shaped profile provides strong bending resistance in one primary direction, making them ideal for floor openings, knock-throughs, and structural alterations.

However, UBs have limitations:

• They are open sections, which means lower torsional resistance.

• They can be bulky in certain design situations.

• Their flanges may not suit all connection types.

• They are not always the most efficient shape for compression or multi-directional loading.

When these factors become important, alternative profiles start to make sense.

Hollow Sections (RHS, SHS and CHS)

Hollow sections — including Rectangular Hollow Sections (RHS), Square Hollow Sections (SHS), and Circular Hollow Sections (CHS) — are closed profiles. That closed shape changes everything.

Why choose a hollow section?

1. Better torsional resistance
Because they are closed sections, hollow profiles perform far better under twisting loads than open sections like UBs or channels. This makes them ideal for frames, columns, and structures subject to lateral forces.

2. Cleaner appearance
Architectural projects often favour hollow sections because they look neater and more symmetrical. In exposed steelwork, this matters.

3. Strong compression performance
For columns, hollow sections distribute stress evenly around the profile. This makes them highly efficient under axial compression.

4. Reduced weight for certain applications
In some cases, an RHS or SHS can achieve required strength with less steel than a comparable UB, depending on the loading and span.

That said, connections can be more complex. Bolting directly into hollow sections usually requires welded plates, end plates, or specialist connectors. So while structurally efficient, they may require more fabrication.

PFC Channels (Parallel Flange Channels)

PFC channels are C-shaped sections with parallel flanges. They are often overlooked but extremely useful.

Where channels make sense:

1. Edge beams and floor perimeters
Channels can sit flush against masonry or slabs more easily than a UB in some layouts.

2. Situations requiring back-to-back sections
Two channels bolted together can form an efficient built-up section, sometimes used in portal frames or heavier-duty applications.

3. Lighter structural solutions
For smaller spans or secondary steelwork, a channel may provide adequate strength without the bulk of a UB.

However, because they are open sections, channels are more susceptible to twisting under load unless restrained. Proper lateral restraint is essential in design.

Bespoke and Built-Up Sections

Sometimes neither a UB nor a standard hollow section is the right answer.

In larger or more complex builds, engineers may specify:

• Built-up plate girders

• T-sections

• Boxed sections formed from welded plates

• Asymmetric sections for specific load paths

These solutions are usually driven by engineering requirements rather than convenience. For example:

• Long spans with height restrictions

• Heavy point loads

• Irregular load distributions

• Architectural constraints

Custom profiles allow engineers to place material exactly where it is needed, improving efficiency while meeting strict design requirements.

Strength vs Weight Considerations

Steel selection is not just about maximum strength. It’s about efficient strength.

A UB may offer excellent bending capacity, but if torsion, lateral loading, or compression dominate the design, another profile could achieve the same performance with less material.

Reducing weight can:

• Lower fabrication and material costs

• Reduce lifting requirements on site

• Simplify installation

• Decrease foundation loads

Every project benefits from using the right shape for the job rather than defaulting to the most common option.

Connection Practicalities

Connections often drive the final choice of section.

For example:

• UBs are straightforward for bolted end plate and flange connections.

• Hollow sections may require welded plates for bolting.

• Channels can simplify certain edge or flush connections.

• Built-up sections may allow tailored connection plates to be integrated from the outset.

Ease of fabrication, access for bolting, fire protection requirements, and on-site handling all play a role in deciding which section works best.

Choosing the Right Profile

There is no “best” section — only the most appropriate one for a given design.

A structural engineer will assess:

• Span and loading

• Lateral stability requirements

• Connection detailing

• Architectural considerations

• Installation constraints

• Budget

In many straightforward domestic alterations, a Universal Beam is perfectly suitable. But in more complex builds — or where space, weight, appearance, or torsion matter — hollow sections, channels, or bespoke profiles may offer clear advantages.

Understanding these alternatives allows builders, designers, and property owners to make informed decisions rather than relying on habit.

If you’re unsure which section your project requires, always consult a qualified structural engineer before ordering steel. The right choice at design stage can prevent costly changes later on.