Which one of the following statements is correct under safety provisions of the ACI code ?
- ADesign strength is greater than required strength and design moment is greater than required momentCorrect
- BDesign strength is greater than required strength and design moment is less than required moment
- CDesign strength is less than required strength and design moment is greater than required moment
- DDesign strength is less than required strength and design moment is less than required moment
Solution
Concept
ACI strength design requirement
Formula
φ Sn ≥ U
Step-by-step solution
1. ACI requires the design strength φSn to be at least the required strength U. 2. Similarly the design moment capacity must be at least the required moment.
Explanation
Capacity reduction factors are applied to the nominal strength, and the result must not be less than the factored load effect.
Why the other options are wrong
Options with "less than" mean the member is unsafe.
Shortcut
Design strength ≥ required strength.
Correct answer: A) Design strength is greater than required strength and design moment is greater than required moment