AS3990 vs AS4100 – Why Equipment Design Needs a Different Rulebook
When people talk about steel design in Australia, the conversation usually begins and ends with AS4100. And for buildings, platforms, and general structures — that’s fair. But when it comes to mechanical equipment, mobile plant, or fabricated frames supporting dynamic loads, there’s another standard that often gets overlooked: AS3990.
At Trang Imagineering, we work with both. Here’s why AS3990 matters, when you should use it, and how we apply it to the kinds of jobs most engineers shy away from.
What Is AS3990?
AS3990 is the Australian Standard for Mechanical Equipment – Steelwork. It governs the design and verification of steel structures that are part of mechanical systems — like skids, machinery frames, pump bases, and equipment enclosures.
Unlike AS4100 (which assumes static loads, predictable conditions, and structural building assumptions), AS3990 is built for the messy reality of plant equipment. That includes:
Cyclic loads
Dynamic vibration
Mechanical interactions
Component integration
In other words: AS3990 is where mechanical engineering meets structural compliance.
How Is AS3990 Different from AS4100?
While AS4100 and AS3990 share a similar design foundation, they’re built for very different types of work. Here’s a breakdown of the key differences:
Application:
AS4100 is used for structures like buildings, walkways, and platforms. AS3990 is used for mechanical systems — like equipment frames, skids, and machinery supports.Loading Conditions:
AS4100 is based around static loads and predictable building forces. AS3990 factors in dynamic loads, vibration, and shock cycles typical of rotating or mobile equipment.Connection Design:
AS4100 focuses on structural bolted and welded joints. AS3990 considers equipment interfaces, including mounting brackets, mechanical fixings, and bolted bases.Fatigue Considerations:
AS4100 gives limited attention to fatigue. AS3990 specifically deals with fatigue and cyclic stress, which is critical for high-duty or vibrating systems.Stress Limits:
AS4100 applies structural safety factors. AS3990 adjusts stress limits to suit mechanical duty, load frequency, and service class.
In short — if it’s plant, machinery, or anything that moves or vibrates, AS3990 is usually the right tool for the job.
How Trang Applies AS3990 in Practice
We specialise in projects that involve complex, non-standard mechanical systems — like:
Mobile plant frames and towable skids
Pressure equipment mounts and baseplates
Ag machinery chassis and toolbars
Brackets for hydraulic/pneumatic equipment
Equipment with high-duty cycles or repetitive shock loads
We apply FEA analysis, custom load modelling, and fatigue simulations to validate compliance with AS3990. Then we certify it with a full engineering report ready for tender submission, council acceptance, or site installation.
Who Needs AS3990?
If your structure:
Moves
Supports rotating or reciprocating equipment
Carries mechanical loads (not just people or static weight)
Needs fatigue analysis or duty-specific design
…then you need AS3990.
It’s not a nice-to-have — it’s the correct standard. Using AS4100 on a mechanical system might get you through drafting, but it won’t hold up in a serious audit, inspection, or worst-case scenario.
Why Clients Trust Trang With Complex Certification
We don’t just know the standards — we know when and how to apply them. We regularly deliver:
AS3990 certification for fabricated machinery
Hybrid AS4100/AS3990 verification reports for mixed structural/mechanical systems
Modifications and retrofits to bring existing gear into compliance
Practical, buildable solutions that don’t break the jobsite budget
Whether you’re designing a one-off machine or upgrading equipment for a mine site shutdown, Trang Imagineering is ready to help with standards-driven, real-world engineering.
Need help deciding whether AS3990 or AS4100 applies to your job?
We’ll figure it out for you — and make sure the job gets certified, fast.