In short: The AS 4100 steel structures standard is Australia’s core document for designing steelwork in buildings, structures and cranes using the limit states method. This post explains what it covers, who uses it, how it relies on the AS/NZS 1170 loading standards, and how it compares with AISC 360 and Eurocode 3. It explains concepts only and gives no design values.
What AS 4100 is for
AS 4100 is the Australian Standard titled Steel structures. It is written by the Standards Australia committee BD-001 and sets out the minimum requirements for designing steelwork. It also covers the engineering side of fabricating, erecting and modifying that steelwork. The method it uses is limit states design (more on that below).
The current edition is the third edition, AS 4100:2020. It was published on 21/08/2020 and replaced the 1998 edition, as the Australian Steel Institute’s update note records. Amendment No. 1 followed in September 2021, and the current reissue incorporates it. If you are working from an older copy, check which edition your project specification actually calls up. Always read the current edition yourself. This post explains the ideas in our own words and does not reproduce the standard, which is copyright of Standards Australia.
What the AS 4100 steel structures standard covers
The scope is buildings, structures and cranes constructed of steel. In practice that means the things you see on industrial and commercial sites:
- Portal frames, columns, beams and bracing
- Platforms, mezzanines and support structures
- Crane runway and gantry structures
- Bolted and welded connections between members
- Stability, so the frame does not buckle or sway excessively
- Serviceability, such as deflection and vibration in normal use
The standard also deals with the materials side at a general level. It expects structural steel to come from the recognised product standards, such as AS/NZS 3679.1 for hot-rolled sections, AS/NZS 3678 for plate and AS/NZS 1163 for hollow sections.
What it leaves out
AS 4100 is not a catch-all. A few examples of where you go elsewhere:
- Cold-formed, light-gauge members such as purlins and girts fall under AS/NZS 4600.
- Composite steel-concrete members are designed to AS/NZS 2327.
- Box girders and longitudinally stiffened girders point to AS/NZS 5100.6.
- Very thin steel elements and higher-strength steels sit outside the scope. The exclusions clause lists the limits, so read it in the current edition rather than relying on a summary.
Who uses it
Structural engineers are the main users, but they are not the only ones. Detailers and drafters build their drawings around the connection and member requirements the engineer works to. Fabricators and erectors work to the engineering intent. Certifiers and building surveyors check that the design follows a recognised pathway. Mechanical designers also meet it whenever a machine, platform or lifting frame has to be supported by a steel structure.
The National Construction Code (NCC) gives the standard its legal weight in buildings. Part B1 of NCC 2022 Volume One lists AS 4100 for steel structures and AS/NZS 4600 for cold-formed steel structures in its deemed-to-satisfy provisions. That is why a certifier asks about it at approval time.
Limit states design in plain words
Limit states design asks two questions:
- Will it hold? This is the strength (ultimate) question. Could the structure or a part of it fail, buckle or collapse?
- Will it behave? This is the serviceability question. Will it deflect, vibrate or crack finishes in normal use?
The “design action effects” come from loads that have been scaled up by factors. The “design capacity” of the member or connection is its nominal capacity scaled down by a capacity factor. The design is acceptable when capacity is at least as large as the action effect. The idea is that uncertainty is handled in both the load side and the strength side. Treat any specific factor values as something you read in the standard, not something to carry around in your head.
For historical context, AS 4100 first appeared in limit states format in 1990. Before that, Australian steelwork used permissible stress design under AS 1250. A 2012 presentation hosted by the Australian Steel Institute notes that the limit states approach was based on the American AISC LRFD resistance factors.
How AS 4100 relates to AS/NZS 1170 loads
AS 4100 tells you how strong the steel and its connections are. It does not tell you what loads a building will see. That job belongs to the AS/NZS 1170 series, Structural design actions:
| Part | What it deals with |
|---|---|
| AS/NZS 1170.0 | General principles, limit states, combinations of actions, robustness |
| AS/NZS 1170.1 | Permanent and imposed actions, plus liquid, ground water, ponding and earth pressure |
| AS/NZS 1170.2 | Wind actions |
| AS/NZS 1170.3 | Snow and ice actions |
| AS 1170.4 | Earthquake actions in Australia |
Part 0 is the glue. It sets the general limit states framework and how actions are combined. AS 4100 sits on the other side of the equation and supplies the resistance. Together they let an engineer compare “what the structure must resist” with “what it can resist”.
Two practical points follow from this:
- If you change what a structure is used for, the loads change, and the design needs to be reassessed. A drawing note that says “steel to AS 4100” does not say anything about the loads it was designed for.
- The AS/NZS 1170 commentary states that the series is intended to be applied by a suitably qualified professional. The same goes for AS 4100.
The family of standards around it
Steel work in Australia is not governed by one document. AS 4100 is the design standard, and it works alongside others:
| Standard | Role |
|---|---|
| AS 4100 | Design of steel structures |
| AS/NZS 5131 | Fabrication and erection, including tolerances and construction categories |
| AS/NZS 1554 series | Structural steel welding |
| AS/NZS 2312 | Corrosion protection of steel structures |
| AS/NZS 4600 | Cold-formed steel structures |
The Australian Steel Institute describes AS 4100 and AS/NZS 5131 as working together to deliver design and construction outcomes that are fit for purpose. If you read weld symbols on fabrication drawings, our post on weld symbols on drawings, AS 1101.3 and ISO 2553 explains how that information is communicated.
Overseas equivalents: AISC 360 and Eurocode 3
Readers outside Australia will want to know what the nearest equivalent is. The short version:
- United States: ANSI/AISC 360, Specification for Structural Steel Buildings. AISC announced that the 2022 edition supersedes the 2016 edition. The 2016 edition covers both load and resistance factor design (LRFD) and allowable strength design (ASD).
- Europe: Eurocode 3 (EN 1993), Design of steel structures. It applies to buildings and civil engineering works in steel and is split into parts covering general rules, bridges, towers and masts, silos and tanks, piling and crane-supporting structures. The European Commission’s Eurocodes site tracks how EN 1993 is being revised. It sits alongside EN 1990 (basis of design) and EN 1991 (actions on structures).
- Elsewhere: Other countries have their own, for example GB 50017 in China and IS 800 in India.
AISC 360 vs AS 4100
Both are limit-state style codes. The 2012 comparison mentioned earlier points out some differences in approach. AS 4100 and AISC both sort section elements into three regions (compact, non-compact and slender). Eurocode 3 uses four classes. For compression members, AS 4100 and Eurocode 3 both use several column curves where AISC 360-10 used one.
Those details come from older editions, so do not treat them as current. The point for a reader is that the codes are cousins, not twins. You cannot mix factors, load combinations or capacity equations from one code with another and expect the result to be valid. Use the code your project is governed by, with its own matching loading standard.
Reading AS 4100 on a project
A few habits help when AS 4100 shows up on a drawing or specification:
- Confirm the edition and any amendments.
- Check which loading standard and combinations the design used.
- Find out who the responsible engineer is.
- Check corrosion protection and fabrication requirements, not just the members.
If your steelwork supports plant, platforms or lifting equipment, safety in design thinking helps as early as concept stage. Our Safety in Design service is one place to see how that works. For equipment-led projects, see materials handling equipment, mechanical engineering design and mechanical drafting and 3D modelling. If you have a general question, the Engineering Q&A page is a good place to start, and the full list of our engineering and drafting services is on the services page.
Frequently asked questions
Is AS 4100 a law?
Not by itself. It is a standard, but the National Construction Code lists AS 4100 as a deemed-to-satisfy way to meet its structural requirements for steel structures. In practice that makes it the expected pathway for building approval in Australia. Always check the current NCC edition and any state or territory variations.
What is the latest edition of AS 4100?
The current edition is AS 4100:2020, the third edition, published on 21/08/2020 and replacing the 1998 edition. Amendment No. 1 was issued in September 2021, and the current reissue incorporates it. Check Standards Australia or an authorised distributor for the latest status before you rely on it.
What is the overseas equivalent of AS 4100?
The closest equivalents are ANSI/AISC 360 in the United States and Eurocode 3 (EN 1993) in Europe. All three use limit-state style methods, but the details differ. Do not mix factors, load combinations or equations between codes. Use the one your project is governed by, with its own loading standard.
Does AS 4100 give the loads on a structure?
No. Loads come from the AS/NZS 1170 series: Part 0 for general principles and combinations, Part 1 for permanent and imposed actions, Part 2 for wind, Part 3 for snow and ice, and AS 1170.4 for earthquake. AS 4100 supplies the resistance side of the comparison.
Where to start
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