Material optimisation

The size of the item

On the material cost of the structure itself, around 40% can be saved with a well-calculated, optimised design against an over-sized one.

It cannot be projected onto the whole building — that would be comparing apples with pears. For the other disciplines it cannot be measured as precisely, but a more accurate structure is easier and faster to work to.

Why over-sizing happens

Not through incompetence. The commonest causes:

• too little time: rounding safely upwards is faster than calculating precisely,
• standardisation: the same section everywhere, because it is simpler,
• stacked assumptions: somebody rounds up at every uncertainty,
• missing input: if the weight of the build-up is unknown, the designer works with the worse case. What happens if the input is incomplete.

Where the reserve sits

Member-by-member design

Not every stud carries the same. In LGS manufacturing supports this too: the thicker section goes where the load justifies it. Auto-gauging.

Taking the restraint accurately

In a thin-walled structure the capacity is limited by stability. If the model is more pessimistic than reality, that shows up in material. Restraint.

Connections

Often the connection is the bottleneck, not the member. With a better connection the member can be smaller.

Nesting

Waste is material cost too. Nesting and waste.

When it pays

On larger structures the item often repays the design fee several times over. On a small building the absolute figure is small, so we look at it within a plan review instead. Plan review.

What we do not do

We do not optimise at the expense of safety. The design is still to the Eurocodes — the difference is that it is precise rather than rounded up.

The point

Over-sizing is paid for by the client, and they get nothing for it. Optimisation is not risk-taking but accurate work.