FEA in practice: when analysis earns its keep, and what to hand the engineer

Finite element analysis (FEA) breaks a component into thousands of small elements, applies loads and constraints, and solves for the stress and deflection in each one. Modern CAD packages make it possible to produce a colourful stress plot in an afternoon. That is exactly why it is worth being clear about when the plot means something.

Hand calculations come first

Most steelwork and mechanical components are covered by code formulas. A beam under a known load, a bolted connection, a fillet weld, a lifting lug of standard proportions: the Australian Standards (AS 4100 for structural steel, AS 3990 for mechanical equipment steelwork, AS 1418 for cranes and lifting equipment) give methods that a competent engineer can apply in minutes and a reviewer can check just as fast. For these, FEA is slower, harder to review and no more accurate. If an engineer reaches for FEA on a standard member, ask why.

When FEA is the right tool

• Geometry the code does not cover. Castings, machined parts, irregular brackets, cut-outs near loads, anything where the stress concentration cannot be looked up.
• Weight optimisation. Mobile equipment, attachments, lifted items and anything transported by road. FEA shows where material is doing nothing and can be removed while keeping stiffness where it matters.
• Fatigue. Components under cyclic load, such as screens, conveyors, vibrating equipment and anything that gets lifted daily, fail at stress concentrations that hand methods struggle to locate.
• Non-standard lifting equipment. Spreader beams, lifting frames and lugs with unusual geometry. AS 4991 covers lifting devices and expects the design to be justified.
• Assessing existing structures. Where measured deflections or cracking do not match the original design assumptions, or where a structure is being asked to take a load it was never designed for.
• Justifying reuse. Demonstrating that an existing frame or skid can be repurposed rather than replaced.

What the engineer needs from you

An FEA model is only as good as its inputs, and the inputs mostly come from the client. Gather these before the analysis starts and the job goes quickly:

1. Geometry. The CAD model if one exists, otherwise fabrication drawings. Weld sizes, corner radii and plate thicknesses matter, because stress concentrates at exactly those details.
2. Loads and load cases. Not just the operating load. Test loads, transport and tie-down loads, wind, seismic where relevant, impact, and the worst credible misuse. If you do not know the load, say so; measuring or estimating it is part of the job.
3. Material and certificates. Grade, and mill certificates if the item already exists. The difference between Grade 250 and Grade 350 steel is a 40 per cent change in the answer.
4. Boundary conditions. How the part is held: bolted, welded, resting on a surface, pinned. Getting this wrong is the single most common FEA error, and only the person who knows how it is installed can answer it.
5. Acceptance criteria. Which standard applies, what utilisation or safety factor is required, and whether deflection limits matter. Site engineering standards often add their own.
6. History. Inspection findings, cracks, repairs and previous modifications on an existing component.

What a good FEA report contains

You should be able to hand the report to another engineer and have them agree or disagree with it without re-running the model. That means it includes:

• The assumptions, stated plainly: loads, materials, boundary conditions and what was simplified.
• The mesh, and evidence that refining it does not change the answer (mesh convergence).
• A hand calculation cross-check of at least one result. If the FEA says a beam deflects 3 mm and the hand calculation says 30 mm, one of them is wrong and it is usually the model.
• Results against the acceptance criteria, as utilisation ratios rather than just stress plots.
• Recommendations: what to change, what to inspect, or what the safe working limit is.
• RPEQ certification, because the conclusion is a professional engineering service.

A weight optimisation example

A typical case is a transport frame or trailer-mounted skid that has to stay under a road-legal mass. The first pass of the design uses generous sections everywhere. FEA under the transport, lifting and operating load cases shows that most of the structure is below 30 per cent utilisation while a few connections are close to the limit. The engineer thins the lightly loaded members, adds gussets where the load concentrates, re-runs the cases and confirms stiffness has not dropped below the deflection limit. The result is usually a 15 to 25 per cent mass reduction with no loss of margin, and the analysis becomes the justification for the design.