Steel Column Compressive Strength
Hardsteelcolumnsflexural bucklingslenderness
A steel column has effective slenderness ratio gross area mm yield stress MPa and GPa. It has no slender elements. Per AISC LRFD flexural buckling provisions, the design compressive strength is most nearly:
- A866 kN
- B962 kN
- C1,630 kN
- D2,480 kN
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Answer: A. 866 kN
First decide which branch applies. The boundary is 4.71√(E/Fy) = 4.71√(200,000/345) = 113.4. Since KL/r = 120 exceeds it, buckling is elastic and Fcr = 0.877 Fe. The Euler stress is Fe = π²E/(KL/r)² = π²(200,000)/120² = 137.1 MPa, so Fcr = 0.877 × 137.1 = 120.2 MPa. Then Pn = Fcr Ag = 120.2 × 8,000 = 962 kN and φc Pn = 0.90 × 962 = 866 kN. Quoting 962 kN forgets the resistance factor; 2,480 kN is 0.9 Fy Ag, the squash load with buckling ignored, which a slender column can never reach.
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