Module 18
Fabrication, erection and durability
The point at which a design stops being a calculation and becomes an instruction to somebody else — and the two limit states that are reached on site rather than in service.
What this module covers
- Say what determines the execution class, and why it is a determination rather than a preference
- Explain what an execution class actually buys, and what it costs
- Treat corrosion protection as a design-life problem rather than a paint problem
- Identify the details that defeat a coating specification whatever is written on it
- Show why a partly erected frame can be several times less stable than the finished one
- State what the sway imperfection of Module 4 does and does not cover
Lessons
Every calculation in this course has assumed a structure built the way it was drawn. This lesson is about the machinery that makes that assumption true — and about who pays for it.
Start lesson →One is reached slowly over decades, the other in an afternoon halfway through the programme. Neither appears in the frame analysis, and both can govern.
Start lesson →
Module checkpoint
Check what you have taken in
5 questions
Question 1
Moving from EXC2 to EXC3 changes the proportion of butt welds given volumetric NDT from 10% to 20%. By what factor does the tested proportion increase?
Question 2
Unprotected steel in a C5 marine environment corrodes at about 120 µm per year. Over a 50-year design life, how much thickness is lost from each exposed face, in mm?
Question 3
A frame will finish with 4 braced bays and αcr = 12. At one stage, 2 bays are braced and all the steel is standing. Estimate αcr at that stage.
Question 4
A 4 m storey is permitted to be out of plumb by h/300. What is the permitted deviation, in mm?
Question 5
A 200 µm system gives 25 years to first maintenance in C3. How many times must the building be repainted over a 50-year design life?