--------------------- | -------------------- | -------------------------------------- | | Resistance factor | phi = 0.9 | phi_c = 0.9 | | Column curve | (1+lambda^2n)^(-1/n) | 0.658^(lambda_c^2) or 0.877/lambda_c^2 | | n for W-shapes | 1.34 | Implicit in curve | | n for HSS (cold-formed) | 2.24 | Separate HSS provisions | | Effective area (Class 4) | per Clause 11.3.4 | per Section E7 | | Torsional-flexural | Clause 13.3.3 | Section E4 (separate equation) |

Both standards are calibrated to the same SSRC column database and produce near-identical results for hot-rolled I-shapes. Differences emerge for cold-formed HSS where CSA uses a distinct n exponent and for Class 4 sections where the effective width calculation methods differ slightly.

FAQ

Calculation Tips

• CSA S16 uses the minor axis (ry) for slenderness unless bracing restrains the weak axis.
• 350W steel is the most common Canadian structural grade — it provides 17% more capacity than 300W.
• For Class 4 sections, the effective area reduction can significantly lower Cr — verify flange and web slenderness per Clause 11.3.4.
• Adding intermediate bracing at mid-height reduces KL by 50%, often doubling the member compressive resistance.
• The n = 1.34 exponent for hot-rolled W-shapes produces a column curve equivalent to AISC LRFD — less conservative than the n = 2.24 used for cold-formed HSS.

What is the resistance factor φ for columns in CSA S16? The φ factor for compression members is 0.9 per CSA S16:24 Clause 13.3.1.

How does the calculator handle the slenderness reduction? CSA S16:24 uses the factor (1 + λ²ⁿ)^(-1/n) where n = 1.34 for W-shapes (hot-formed). This is based on the SSRC multiple-column curve approach and is equivalent to the AISC LRFD column curve.

Does CSA S16 use different buckling curves for different sections? Yes. The parameter n varies by section type: n = 1.34 for hot-formed shapes (W, S, C), n = 2.24 for cold-formed HSS, and n = 2.24 for structural tubing per CSA S16:24 Clause 13.3.1.

What about combined compression and bending? Clause 13.8.2 interaction is checked for biaxial bending and axial compression using the interaction formula Cf/Cr + Mfx/Mrx + Mfy/Mry ≤ 1.0, with the P-δ amplification factor U1x = ω1/(1 - Cf/Cex) applied where Cex = π²EIx/(KL)².

What is the difference between cross-section resistance and member resistance? Cross-section resistance Cr = φAFy represents the squash load with no buckling — it applies only to very short columns (λ < 0.15). Member resistance accounts for flexural buckling through the slenderness parameter λ and the n exponent. For a typical 4 m column, member resistance is 60-80% of cross-section resistance. The member resistance always governs for practical column lengths.

How does the calculator handle unbraced frame columns? For columns in sway-permitted (unbraced) frames, the effective length factor K ≥ 1.2 per Clause 13.3.2. The calculator accepts user-specified K values. The alignment chart (Annex H) provides approximate K values: K = (1.6 + 2.4GA + 1.6GB + 4GAGB) / (GA + GB + 7.5GAGB)¹/² for sway-permitted frames, where GA and GB are the stiffness ratios at the column ends.