Ever looked at a steel frame going up on a building site and wondered why all the pieces look different? Some are thick and chunky, some are hollow, and others are simple flat plates bolted into place. It’s not random. Every shape of structural steel is designed to do a specific job, in structural design, whether that’s carrying heavy loads, spanning open spaces, or keeping an entire structure stable.
We work with structural steel every day, so we’ve put together a clear guide to the most common steel types and shapes you’ll see on construction projects, what they’re used for, and why engineers choose them.
Why does structural steel come in different shapes
Steel might look simple at first glance, but it’s one of the most important construction products used in modern buildings. The shape of a section has a huge impact on how it performs. The right profile can carry more weight, resist bending, or stay stable under pressure, often while using less material.
That’s why structural steel sections are rolled, fabricated, or sometimes cold-formed into specific forms. Instead of using solid blocks of metal everywhere (which can get heavy and expensive), engineers place the steel where it’s needed most within the shape of the section.
The result? Stronger structures, lighter frames, and more efficient buildings.
UNIVERSAL BEAMS (I-BEAMS)
Universal beams, often called I-beams or RSJs, are some of the most recognisable structural steel sections. Their I-shaped profile concentrates steel in the top and bottom flanges, where bending forces are highest, while the thinner centre web keeps the weight down.
You’ll usually see them supporting floors, roofs, and large openings.
They’re commonly used for:
- Load-bearing walls removed in extensions
- Open-plan layouts
- Commercial floor structures
- Long spans in structural floors and roofs
Because they can carry serious loads across wide distances, a single universal beam can often replace several supporting walls, opening up the space without compromising strength.
UNIVERSAL COLUMNS (H-SECTIONS)
While beams are designed to span horizontally, universal columns are built to handle vertical loads. Their H-shaped profile is thicker through the centre, helping them transfer weight directly down into the foundations.
They’re widely used in steel-framed buildings where multiple storeys need strong vertical support.
You’ll often see universal columns used in:
- Multi-storey building frames
- Mezzanine floors
- Warehouse structures
- Commercial steel skeletons
If something needs to stand firm under constant pressure, there’s a good chance a universal column is doing the job.
PARALLEL FLANGE CHANNELS (C-SECTIONS)
Parallel flanged channel sections, usually called C-sections, are open steel profiles that are lighter than beams but still strong enough for many structural tasks.
Their shape makes them easy to fabricate, drill, bolt, or weld, which is why they’re popular for secondary steelwork and framing.
Common uses include:
- Steel framing systems
- Agricultural buildings
- Solar panel structures
- Transport and plant supports
They’re quick to install and versatile, which helps keep fabrication and installation efficient on-site.
ANGLE SECTIONS (L-SHAPED)
Angle sections might look simple, but they’re incredibly useful. As the name suggests, they’re rolled into an L-shape, making them ideal for connecting different steel components.
You’ll often find them working quietly in the background, tying structural elements together.
Typical uses include:
- Brackets and structural connections
- Supporting frames and edges
- Reinforcing steelwork joints
- Secondary support structures
Sometimes, two angle sections are paired together to create a stronger built-up section, depending on the loads involved.
STEEL PLATES
Steel plates are essentially flat sheets of structural steel and are one of the most versatile steel products used in fabrication, but don’t underestimate them. They’re often the pieces that make everything else work.
Fabricators use plates for:
- Base plates under columns
- Gusset plates connecting beams and braces
- Stiffeners strengthening beams
- Load distribution points
Because they can be cut, drilled, and welded into almost any configuration, steel plates act as the connectors that tie an entire structure together.
HOLLOW STEEL SECTIONS (HSS)
Hollow steel sections are tubular steel profiles with a hollow centre. Unlike open sections, the steel is distributed evenly around the outside, which gives them excellent strength in multiple directions.
They come in three main forms:
- Square hollow sections (SHS)
- Rectangular hollow sections (RHS)
- Circular hollow sections (CHS)
Because of their balanced shape, hollow sections perform particularly well under compression and twisting forces.
You’ll often see them used in:
- Steel building frames
- Architectural structures
- Walkways and bridges
- Marine and outdoor structures
They’re also efficient, strong, and without needing excessive material, which helps control both weight and costs.
RECTANGULAR SQUARE HOLLOW SECTIONS
Square and rectangular hollow sections are especially popular where both structure and appearance matter.
Their clean lines make them a favourite for:
- Exposed steel frames
- Columns in modern buildings
- Structural supports in commercial fit-outs
- Residential steel features
In many projects, the steelwork is deliberately left visible, and these sections provide the strength while still looking neat and consistent.
CIRCULAR HOLLOW SECTIONS
Circular hollow sections distribute forces evenly around their shape, which makes them particularly good at handling loads coming from different directions.
Because of this, they’re often used in structures exposed to wind, movement, or changing loads.
Typical applications include:
- Structural columns
- Bridge supports
- Pylons and towers
- Public architectural structures
Add galvanising or protective coatings, and they’re capable of lasting for decades even in challenging environments.
Structural steel types
Most structural steel used in construction is mild steel, also known as low-carbon steel. Common examples include Structural Steel S235 and Structural Steel S275, which are widely used in general building applications. It provides a good balance of strength, flexibility, and ease of fabrication, which is why it’s widely used across the industry.
When projects require higher performance, engineers might specify:
- High-strength low-alloy steel for increased strength with less material
- Weathering steel that forms a protective rust layer that resists corrosion
- Stainless steel for environments where hygiene, appearance, or exposure is important
All structural steel must meet recognised standards such as Eurocode 3, EN 1993-1-1, and EN 10025. These requirements ensure products meet the Construction Products Regulations and wider EU legislation for structural steel. In simple terms, what’s designed on paper performs exactly as expected on site.
Why choosing the right steel section matters
Every beam, column, plate, or hollow section plays a part in how a structure behaves. Choosing the right section means loads travel efficiently through the structural steelwork, foundations stay sensible in size, and construction runs smoothly.
Get it wrong, and you either end up over-engineering the structure or solving problems further down the line.
From iconic structures like the Empire State Building to everyday home extensions and warehouses, structural steel keeps proving the same point: when it’s designed and fabricated properly, it just works.
Need structural steel fabrication for your project?
Whether it’s RSJs, columns, hollow sections, or bespoke fabricated steel components, working with experienced steel fabricators makes all the difference. Properly specified steelwork ensures your structure performs exactly as intended, safely, efficiently, and is built to last.
If you’re planning a project and need reliable structural steel fabrication, it’s always worth speaking to professionals who understand the practical side of how these sections perform in the real world.