Find the correct statement regarding the assumption of limit state design under compression member as per IS 456:2000.
- AThe minimum compressive strain in concrete in axial compression is 0.002.
- BThe minimum compressive strain in concrete in axial compression is 0.0002.
- CThe maximum compressive strain in concrete in axial compression is 0.002.Correct
- DThe maximum compressive strain in concrete in axial compression is 0.02.
Solution
Concept
In IS 456:2000, the maximum compressive strain in concrete under pure axial compression is taken as 0.002.
Formula
εcu (axial compression) = 0.002; εcu (flexure) = 0.0035
Step-by-step solution
1. Recall the IS 456 assumptions for the limit state of collapse in compression members. 2. Under pure axial compression, the maximum compressive strain in concrete is 0.002. 3. In bending (flexure), the maximum strain is 0.0035. 4. The code gives a maximum limit, not a minimum. So option C is correct.
Explanation
IS 456 limits the strain in concrete under pure axial compression to 0.002. At this strain the parabolic stress-strain curve of concrete reaches its peak stress. This is a maximum value, not a minimum value.
Why the other options are wrong
A: 0.002 is a maximum, not a minimum. B: 0.0002 is wrong, and the code does not give a minimum strain. D: 0.02 is ten times too large and is not a code value.
Shortcut
Axial compression = 0.002 (maximum); bending = 0.0035 (maximum).
Common mistake
Mixing up 0.002 (axial) with 0.0035 (flexure), or reading it as a minimum strain.
Correct answer: C) The maximum compressive strain in concrete in axial compression is 0.002.