Design by testing

Why it is needed

The behaviour of thin-walled structures is complex: the stability modes interact, connections fail in the sheet, and the contribution of the lining is hard to model.

Calculation handles these conservatively: safe, but often an underestimate of the real capacity. Testing measures the actual behaviour instead.

Where it is typical

Manufacturers’ products

Manufacturers often verify the capacity of profile families, bracing systems and connectors by testing, and derive design values from it.

Sheathing-braced walls

The capacity of a board-braced wall is very hard to determine by calculation alone — here test results provide the basis.

Bespoke connections

Where a non-standard connection is made and repeats in large numbers, testing can pay for itself.

What makes it acceptable

“Trying it out” is not enough. The standard prescribes:

• the test arrangement, which models the real action,
• the number of specimens, because the scatter in results has to be handled,
• the statistical method of evaluation, which yields the design value,
• the scope of application: the range over which the result is valid.

That last one is the most common source of misunderstanding: a test result cannot be generalised at will — extension has rules.

The practical consequence

Manufacturer data is worth having

If a product carries a test-based design value, use it: it is better than conservative calculation.

But check its validity

For which arrangement, which material thickness, which fixing it applies. If the project differs, the value does not apply.

One-off testing rarely pays

Not for a single house. For series production and repeating structures the cost of testing is spread out, and it can bring significant material savings.

The point

Testing is not a way round the rules but the other route the standard offers. The key is the scope of validity: a test is valid for exactly what was tested.