The 'fatigue' design of steel bridges in India follows IS 1024. The key parameter controlling fatigue life is:
Choose the correct answer
Maximum stress (peak tensile stress only)
Stress range Δσ = σ_max − σ_min — fatigue life governed by range, not peak; detail category from connection type
Only dead load stress
Average stress over the life of the structure
Correct Answer
B. Stress range Δσ = σ_max − σ_min — fatigue life governed by range, not peak; detail category from connection type
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Fatigue life: number of cycles N to failure depends on: stress range Δσ = σ_max − σ_min (NOT peak stress). S-N curve: log(N) = A − m×log(Δσ). FAT class (fatigue detail category) depends on: type of connection, weld geometry, direction of loading. IS 1024 (now largely replaced by IS 800 Cl. 13): Δσ ≤ allowable range for given N cycles. Variable amplitude: Miner''s rule Σ(ni/Ni) ≤ 1.0.
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