Module 21 · Lesson 21.1
The sequence
Sixteen steps, and why the order is the point rather than the list.
Why this matters
Every technique in this course has been taught separately. On a project they arrive together, in an order, under time pressure, and the order is what decides whether they help.
The sequence below is not a procedure to follow mechanically. It is an ordering that puts the cheap, consequential decisions before the expensive, reversible ones — because the commonest way a computational exercise goes wrong is that a model gets built before anybody decided what question it was for.
By the end of this lesson you should be able to
- State the sixteen steps and the phase each belongs to
- Explain why prediction precedes model construction
- Say what each phase costs and what it protects
- Recognise when a step has been skipped
What you should already know
- All of Stages A to D — this module assembles them rather than adding to them
- The model record and the three-stage check in particular (Module 13)
Before anything is built
1. Problem definition. What engineering question must be answered, in one sentence. Everything downstream follows, and a model without one will eventually be asked the wrong question.
2. Concept options. Several genuinely different forms, not variations of one. Module 2's divergent half, done deliberately.
3. Parametric variables. What you intend to vary, and what you are fixing. Module 3: parameterise the uncertain and the variable, and state what has been fixed.
4. Digital workflow. Where the geometry comes from, where results go, and what is lost at each handover.
Deciding the model
5. Analytical model strategy. Whole structure or component, one dimension or three, and what the model will not be able to answer.
6. Element selection. From the required outputs. One-dimensional for frame forces; two for slabs and walls; three only where you must.
7. Solver selection. Linear, second-order or nonlinear — chosen from the expected behaviour, not from what ran last time. Module 11's first lesson: list the nonlinear features before choosing.
8. Prediction. The step that is skipped most and costs least. Estimate the answer now, in writing, before the model exists.
Steps 1 to 8 cost a morning between them and they decide almost everything. Steps 9 onwards cost weeks and can only implement what steps 1 to 8 decided.
Building and checking
9. Model construction. With the diagnostics of Module 12 run as you go rather than at the end: counts, connectivity, units, restraints.
10. Verification plan. Written before the results arrive, so it is not shaped by them. What check, against what, and what agreement would count.
11. Sensitivity study. Which inputs the answer depends on, with ranges that have a stated basis.
Exploring and deciding
12. Optimisation study. Where the question is 'which of these' rather than 'is this adequate'.
13. Carbon comparison. Computed the same way for every option, with the ranking tested against the uncertainty in its own factors.
14. AI-use assessment. Whether any part of this has a legitimate machine-learning role — and for each, whether a deterministic method exists.
15. Model review record. Purpose, assumptions, exclusions, limitations, verification, sign-off.
16. Recommendation. What you advise, on what evidence, and what would change it.
Recognising a skipped step
Each one leaves a characteristic mark:
| Skipped | How it shows |
|---|---|
| 1 Problem definition | The model is asked a question it was not built for, and answers |
| 2 Concept options | One scheme, developed in detail, with no evidence it was the right family |
| 7 Solver selection | A linear analysis of something whose αcr is 3 |
| 8 Prediction | Every result is 'about what I expected', afterwards |
| 10 Verification plan | The checks that were run are the ones that passed |
| 11 Sensitivity | A single answer with no idea what it depends on |
| 15 Model record | Only the author can check the model |
The two most consequential are 8 and 10, and both are free.
Try it
Integrated project workspace
Choose a brief and work the sixteen steps. The prediction cannot be entered once the analysis has run, because a prediction made afterwards is not one.
Project brief
- Steps completed
- 0 of 16
- Before any model (1–8)
- 0 of 8
- Prediction recorded
- no
- Verification plan recorded
- no
Once this is pressed, step 8 locks. That is the whole mechanism: a prediction written after seeing the result is a search for reasons the number might be right.
Six-storey office, 12 m grid proposed
8 000 m² over six storeys. The architect proposes a 12 m column-free grid for letting flexibility. The client has committed publicly to an embodied-carbon target. Floor zone agreed at 1 100 mm including services.
The engineering question, in one sentence.
Several genuinely different forms, not variations of one.
What you will vary, and what you are fixing.
Where geometry comes from, where results go, what is lost.
Whole or component, 1D/2D/3D — and what it will NOT answer.
From the required outputs.
List the nonlinear features first.
Estimate the answer NOW, before the model exists.
With the diagnostics run as you go.
Written before results arrive. What check, against what.
Which inputs it depends on, with ranges that have a basis.
Where the question is 'which of these'.
Same method for every option; test the ranking.
Any legitimate role? Does a deterministic method exist?
Purpose, assumptions, exclusions, limitations, sign-off.
What you advise, on what evidence, what would change it.
8 of the first eight steps are still empty. Those cost about a morning between them and decide almost everything; steps 9 onwards cost weeks and can only implement what they decided.
What none of these steps supplies
- An expectation of what the structure does. Every check depends on having one, and it comes from Structural Behaviour rather than from any procedure.
- The judgement that the brief has already given away the answer — which is what the module's worked project turned on.
- How much checking is enough. Module 13 said it should follow the consequence; judging the consequence is not on any list.
What this shows: Ten of the sixteen steps come before the first result is read — and the two that cost nothing, prediction and the verification plan, are the two most often skipped.
Check yourself
Why does the sequence put prediction (step 8) before model construction (step 9)?
Practice
Of the sixteen steps, how many are completed before any model is built?
Worked example
Which steps are free and which are skipped
Given
- The sixteen-step sequence, of which eight happen before any model exists
Find
Which steps cost nothing and which get left out
Worked example
Where a model belongs in the sequence
Given
- A project engineer proposes to start by building the model
Find
What would be lost
Practice
Of the sixteen steps, eight happen before any model exists. What percentage of the sequence is that?
Check yourself
Why does the sequence put solver selection before model construction?
Summary
- Steps 1 to 8 cost a morning and decide almost everything
- Steps 9 onwards cost weeks and only implement what was already decided
- Prediction before construction, or it is rationalisation
- The verification plan is written before the results, or it is shaped by them
- Each skipped step leaves a characteristic mark, and the two most costly to skip are free
This is educational material. It uses simplified examples to teach principles, and must not be relied on for real design or safety-critical decisions. Module overview and checkpoint