Phase 7 · Pass the examination

Critical structural details

Three at minimum, chosen because they are critical to your scheme — not because they are the ones you can draw.

Who this is for:Candidates at any stage ·IMIStructE members moving to MIStructE

A minimum of three, and the word doing the work is critical — generic and simple typical details are explicitly not acceptable.

What is expected

Institution of Structural Engineers

A minimum of three details would ordinarily be expected.
The critical details vary with the question but may include cantilever connections, major splices and retaining wall details.
On the supplementary paper, candidates must select the critical details from the chosen scheme and prepare detailed drawings with dimensions as appropriate. Generic and simple typical details would not be acceptable.

Critical details ordinarily expected: 3minimumGeneric and simple typical details would not be acceptable.
Section 2d — drawings and critical details: 20marksA minimum of three critical details would ordinarily be expected.
Part b — critical structural details: 20marksA minimum of three details; generic or simple typical details are not acceptable.

From Exam Guidance and Instructions — Chartered Membership Examination, Institution of Structural Engineers.

Which details are critical

A detail is critical when the scheme depends on it — when getting it wrong would change the design, and when it is where the load actually has to be resolved.

Ask which junctions in your scheme are doing something difficult:

Where the load path changes direction or transfers. Transfer beams onto columns, hangers, changes of frame.
Where the stability system connects. Bracing connections, shear wall to slab, core to frame.
Where there is a discontinuity. Movement joints, major splices, changes of material.
Where a cantilever is supported, including the back-span and any tie-down.
Where the ground is involved. Retaining wall stems and bases, pile caps, ground beams.
Anything unique to your scheme. If you proposed something unusual in 1a, its key junction is by definition critical.

A simply-supported beam-to-column bolted cleat is a typical detail, not a critical one. Drawing three of those is the failure mode the instructions are warning about.

How to draw one

Each detail wants: the members meeting, dimensioned; the connection medium — bolts, welds, reinforcement, bearing — indicated by type and rough size; a note of what it is transferring; and a label saying which part of the scheme it belongs to.

Annotate the force path through it. A note reading "tie force 320 kN taken through the cleat into the slab reinforcement" shows you understand what the detail is for, which is what is being marked.

On the supplementary paper this is a quarter of the marks

Part b is worth 20 of 80. That makes it proportionally the most valuable detailing section of any of the three papers, and it is worth practising specifically — selecting details from a scheme you have just invented, under time pressure.

Is this detail actually critical?

The load path changes direction, transfers, or is resolved here
It is where the stability system connects to the rest of the structure
There is a discontinuity — a movement joint, a major splice, a change of material
A cantilever is supported here, including its back-span or tie-down
The ground is involved — a retaining wall stem or base, a pile cap, a ground beam
It is unique to the scheme I proposed in the first section
Getting it wrong would change the design, not just the drawing

7 items · saved in this browser only

Ticked locally in this browser. If a detail satisfies none of these, it is a typical detail, and the instructions say those are not acceptable.

Drawing the details

Worth doing

Dimension the members meeting at the junction
Indicate the connection medium by type and rough size
Annotate the force being transferred, with a magnitude if you have one
Label which part of the scheme each detail belongs to
Draw at least three

Avoid

Submit a standard beam-to-column cleat as a critical detail
Draw three variations of the same junction
Detail reinforcement bar by bar — estimating standard is enough
Leave a detail unlabelled and unplaced
Run the section over on the supplementary paper, where it is worth a quarter of the marks