Module 14
Water-retaining and containment structures
A tank does not fail by collapsing — it fails by leaking, and the crack that leaks usually formed before it was ever filled.
What this module covers
- Explain why crack width, not strength, governs a containment structure
- Derive the critical steel ratio, and say what happens either side of it
- Calculate the restrained early-thermal strain and the crack it causes
- Distinguish a through crack from one with a compression zone
- Say what actually reduces early thermal cracking
- Explain autogenous healing and what it cannot be relied on for
Lessons
Why the critical load case happens in the first three days, and the ratio that decides whether cracking is controlled at all.
Start lesson →Why the pour sequence is a structural decision, and what a crack limit is really protecting.
Start lesson →
Module checkpoint
Check what you have taken in
6 questions
Question 1
Concrete with fct,eff = 2.0 N/mm² and grade 500 steel. What is the critical steel ratio, as a percentage?
Question 2
What happens to a fully restrained member with less than the critical steel ratio?
Question 3
A wall restrained at R = 0.4 with T₁ = 40°C. Taking α = 12 × 10⁻⁶ and K = 0.65, what is the restrained strain, in microstrain?
Question 4
A 250 mm wall with 40 mm cover and H12 bars. What is the surface zone hc,eff, in mm?
Question 5
Why is a higher concrete grade unhelpful in a water-retaining structure?
Question 6
A 200 mm wall retains 5 m of water. What is the hydraulic gradient?