Consider the following statements related to the limit state design criterion for a safe design of the structure: 1.The structure or its elements should not collapse when subjected to the design loads. 2.The structure should not become unfit for use due to cracking or excessive deflection. 3.The structure should reach a limit state during its design life. Which of the above statements are correct?
- A1 and 2 onlyCorrect
- B2 and 3 only
- C1 and 3 only
- D1, 2 and 3
Solution
Concept
A safe design must not reach any limit state (collapse or serviceability) during its design life.
Step-by-step solution
1. Statement 1: The structure must not collapse under design loads. This is the limit state of collapse. Correct. 2. Statement 2: The structure must not become unfit due to cracking or excessive deflection. This is the limit state of serviceability. Correct. 3. Statement 3: The aim of design is that the structure should NOT reach a limit state during its design life. So this statement is wrong. 4. So only 1 and 2 are correct. Answer is (A).
Explanation
In limit state design, the structure must be safe against collapse and must also stay fit for use. A limit state is an unacceptable condition, so a safe structure should not reach it during its design life. So statements 1 and 2 are correct and statement 3 is wrong.
Why the other options are wrong
B: Statement 3 is wrong. C: Statement 3 is wrong, and statement 2 is missing. D: Statement 3 is wrong.
Shortcut
Limit state = failure condition. A good design should NEVER reach it.
Common mistake
Reading statement 3 quickly and not seeing that it says 'should reach' instead of 'should not reach'.
Correct answer: A) 1 and 2 only