Which limit state governs material toughness requirements under AASHTO specifications?

• A. Fatigue limit state
• B. Fracture limit state
• C. Fatigue I
• D. Fatigue II

Answer: (B)

Material toughness relates to a body's ability to resist crack initiation and slow, or prevent, unstable fracture when flaws are present. In AASHTO specifications, the fracture limit state is the one that ensures this behavior—the structure must not fracture catastrophically even with cracks, under the anticipated loads. Toughness is essentially about resisting fracture, so the fracture limit state directly governs material toughness requirements.

Fatigue limit states, including Fatigue I and Fatigue II, focus on repeated, cyclic loading and the growth of cracks over time, which is a different failure mechanism from sudden fracture due to existing flaws.