The ultimate tensile strain in steel is
- A5–15 times more strain than concrete at collapse
- B15–25 times more strain than concrete at collapse
- C25–35 times more strain than concrete at collapseCorrect
- D35–45 times more strain than concrete at collapse
Solution
Concept
Ductility of reinforcement compared with concrete
Step-by-step solution
1. Ultimate compressive strain of concrete = 0.0035. 2. Steel can stretch to about 10 percent or more (0.10–0.12) before fracture. 3. The ratio is about 0.10/0.0035 ≈ 28, i.e. in the range 25–35 times.
Explanation
Steel is far more ductile than concrete. Its ultimate strain at fracture is many times the crushing strain of concrete, which is why under-reinforced beams give warning before failure.
Why the other options are wrong
The range 5–15 or 15–25 would imply a fracture strain of only 1.8–8.8%, which is lower than that for reinforcing steel. 35–45 times would need more than 12–16%.
Shortcut
Concrete 0.0035; steel ≈ 0.10 → about 30 times.
Common mistake
Comparing the yield strain instead of the ultimate strain.
Correct answer: C) 25–35 times more strain than concrete at collapse