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

A quick practical test for "limit state of strength" is to ask whether this condition, if it occurred, would mean the structure can no longer safely carry its load at all.

1. Fire: handled as a special, separate design case, not a routine strength-limit consideration.
2. Failure by excessive deformation: yes, if deformation grows enough to threaten stability or collapse, the structure has genuinely lost load-carrying capacity, which is exactly a strength-limit condition.
3. Corrosion: a slow durability issue affecting long-term service life, not an immediate strength failure.
4. Repairable damage or crack due to fatigue: being repairable, it is a serviceability issue, not a loss of overall capacity.

So the factor included in the limit state of strength is failure by excessive deformation.

Answer 2

A third way is to recall the standard, specific list of failure modes that codes place under the limit state of strength, and check which option appears on that list.

The limit state of strength is typically defined to include: loss of equilibrium of the structure (overturning or sliding), failure by rupture or excessive yielding, buckling of compression members or elements, and failure caused by transformation of the structure into a mechanism through excessive deformation. Everyday durability and cracking issues are deliberately kept outside this list, under a separate serviceability category.

1. Fire: does not appear in the standard strength-limit-state list above; it is addressed through a separate fire-design provision entirely.
2. Failure by excessive deformation: appears directly in the standard list, as excessive deformation leading to instability or mechanism formation is one of the explicitly recognized strength-limit-state failure modes.
3. Corrosion: does not appear in the strength-limit-state list; it belongs to the durability or serviceability considerations instead.
4. Repairable damage or crack due to fatigue: also does not appear in the strength-limit-state list, since repairable cracking is treated under serviceability, not collapse-level safety.

Matching each option against the codified list of strength-limit-state failure modes confirms only excessive deformation belongs there.

Therefore, the correct answer is failure by excessive deformation.