Design calculations in the exam

You choose which members are principal structural elements, and you choose how far to check each one. Both choices are being marked.

Choosing the five to seven

The instructions give the likely candidates. For building structures: main members in trusses, portal frames and arches; transition and transfer members and members with high point loads; cantilever members; vertical structures with high load concentration or significant out-of-balance moments; members of the stability system; foundations including piles, pile caps, reinforced rafts and pads, and balancing beams; retaining walls; and any special element unique to your scheme.

For bridge structures: the deck; the main deck support structure; the vertical structure; the stability system; and the foundations including piles, pile caps and reinforced pads.

Most schemes will not contain all of these. Choose the ones that are structurally decisive in your scheme — the members whose failure would matter and whose sizing drives the rest.

"Repetitive and simple calculations are not required"

This sentence is worth reading twice, because candidates routinely lose an hour ignoring it.

You do not need to design every beam. You do not need multiple load cases. You need the worst case, checked properly, for each principal element. A candidate who designs three typical floor beams at different spans has spent the time that should have gone into the transfer structure and the foundations.

Depth of checking is a judgement being marked

Bending, shear and a span/depth deflection check is the stated baseline for most members. The extra marks come from recognising where that baseline is not enough — and saying so.

Web buckling under a concentrated load is the example the instructions give. Others that commonly matter: lateral-torsional buckling of an unrestrained beam; punching shear at a flat-slab column; overturning and sliding of a retaining wall; uplift on a light structure; and local effects at a transfer.

You do not need to complete every additional check to earn the recognition. Naming it, saying why it governs here, and showing the check that matters is the mark-earning move.

Keeping it legible

The instruction is that calculations be clear and easy to follow, and that is a marking criterion in a section worth over a fifth of the paper.

• One element per page, headed with what it is and where it sits.
• State the loading and its source at the top, once.
• Show the load path down to the foundation, so a marker can follow it.
• Box the answer — size, grade, and the check that governed.
• State assumptions where you make them, not in a preamble nobody reads.