By QED Consulting Engineers — structural & civil engineers, Notting Hill, Melbourne
Structural steel is the backbone of most warehouses, commercial buildings and larger residential projects. Designing it involves two things: sizing the steel members for the loads, and designing the connections that hold them together — and the connections are where a surprising amount of the engineering happens. Steel design in Australia is carried out to the standard AS 4100.
Here's how structural steel design works and why connections matter as much as the beams themselves.
What is structural steel design?
Structural steel design is the engineering of hot-rolled steel members — universal beams, universal columns, channels and hollow sections — into a frame that safely carries the building's loads. It covers working out the loads, selecting members strong enough to carry them without excessive deflection, and designing how those members join.
This is the heavier end of steel construction. It's distinct from light gauge steel (LGS), which uses thin cold-formed sections for framing — a different material and a different design standard. (See our guides on light gauge steel design for that side.)
Why connections are so important
People picture steel design as choosing beam sizes. In practice, the connections often take more engineering thought than the members. A beam is only as good as how it's joined to the columns and other members around it — and a poorly designed connection is a common failure point.
Connections come in different forms depending on what they need to do:
- Simple (pinned) connections transfer shear but allow rotation
- Moment connections are rigid and transfer bending, keeping a frame stable
- Base plates connect columns to their footings and transfer load to the ground
Each is designed for the forces it carries, using bolts, welds or both. Getting the connection type right is fundamental to how the whole frame behaves.
What the engineer designs
A structural steel package typically includes:
- Member sizing for beams, columns and bracing
- Connection design — bolted and welded details
- Base plates and holding-down bolts into the footings
- Bracing to keep the frame stable against lateral loads
- Design documentation to AS 4100 for the building permit
For complex or non-standard elements, engineers use finite element analysis (FEA) to model real-world behaviour before finalising the design.
Design vs detailing — what's the difference?
Two distinct stages, easily confused. Design determines what the steel needs to be — the members, the connections, the forces. Detailing turns that design into fabrication (shop) drawings the fabricator builds from, showing every dimension, hole and weld.
Both are needed, and clear coordination between them keeps fabrication accurate and avoids costly rework on site.
Where structural steel is used
Structural steel appears across the projects our commercial and industrial engineering team designs — portal frame warehouses, mezzanines, industrial buildings — and in residential work where long spans or heavy loads call for steel beams and columns. Wherever the loads or spans exceed what timber or lighter systems can handle, structural steel earns its place.
Got a project that needs structural steel?
Talk to a Melbourne structural engineer about the design and documentation.
Frequently asked questions
What does structural steel design involve?
Sizing steel members for the loads and designing the connections that join them, documented to AS 4100 for the building permit.
What's the difference between structural steel and light gauge steel?
Structural steel uses heavier hot-rolled members (beams, columns); light gauge steel uses thin cold-formed sections for framing. They're different materials designed to different standards.
Who designs steel connections?
A structural engineer designs the connections — simple, moment or base-plate — for the forces they carry, using bolts and welds.
What's the difference between steel design and detailing?
Design works out what the steel must be; detailing produces the fabrication drawings the fabricator builds from. Both are required.
