Question

Which of the following factors is included in the limit state of strength?

• A. Fire
• B. Failure by excessive deformation
• C. Corrosion
• D. Repairable damage or crack due to fatigue

Hint:

Strength limit state is about {safety against collapse}. Serviceability is about {comfort/appearance} (deflection, cracking) without collapse.

Answer 1

The Correct Option is B

Step 1: Understand what “limit state of strength” means.
Limit state of strength refers to a condition related to collapse or failure of the structure, where the structure becomes unsafe.
It includes failures such as yielding, buckling, fracture, instability, or deformation leading to loss of load carrying capacity.
Step 2: Check each option with respect to strength (collapse) criteria.
(A) Fire: Fire is generally treated as an accidental/exceptional loading condition, not a normal strength limit state factor.
(B) Failure by excessive deformation: If deformation becomes excessive such that the member loses stability or load capacity, it is treated under strength/collapse considerations. Hence, this is the best match.
(C) Corrosion: Corrosion is mainly a durability issue and affects long-term performance, not directly a strength limit state factor in standard MCQ classification.
(D) Repairable damage or crack due to fatigue: Fatigue cracking is usually treated under fatigue/durability or service life criteria and is not taken as the primary “strength limit state” factor in such MCQs.
Step 3: Conclusion.
Therefore, the factor included in the limit state of strength (collapse-type consideration) is (B) Failure by excessive deformation.

Answer 2

Indian and international codes classify all limit states into essentially two broad categories: the limit state of strength (collapse), concerned with safety and the load-carrying capacity of the structure, and the limit state of serviceability, concerned with the structure's performance in normal use (deflection, cracking, vibration, durability, and so on). Sorting each option into one of these two categories settles the question directly.

1. Fire: Resistance against fire is generally treated separately as an accidental or exceptional design situation (fire resistance design), rather than being grouped under either the routine strength or serviceability limit states.
2. Failure by excessive deformation: When deformation becomes large enough that the structure loses its ability to carry load safely (such as through instability or loss of equilibrium caused by the deformation), this falls squarely under the strength or collapse category, since it directly concerns the structure's safety and capacity, not just its everyday serviceability.
3. Corrosion: Corrosion affects long-term durability and is classified under durability or serviceability considerations, since it degrades performance over the service life rather than representing an immediate strength or collapse failure mode.
4. Repairable damage or crack due to fatigue: Because this damage is explicitly described as repairable, it is treated as a serviceability-level concern (affecting appearance, tightness, or long-term performance) rather than an outright loss of load-carrying capacity.

Sorting each option by whether it concerns the structure's safety and capacity or its everyday serviceability places excessive-deformation failure squarely in the strength category.

Therefore, the correct answer is failure by excessive deformation.