Question 1

Which formula does the capacity use?

Accepted Answer

The AISC 360-16 E3 column curve. First Fe = π²E/(KL/r)² is computed. If KL/r ≤ 4.71√(E/Fy) the column buckles inelastically and Fcr = 0.658^(Fy/Fe)·Fy; otherwise it buckles elastically and Fcr = 0.877·Fe. The design capacity is φPn = 0.90·Fcr·A (LRFD).

Question 2

What is the effective length factor K?

Accepted Answer

K converts the real column length into the equivalent pinned-pinned buckling length: 1.0 for pinned–pinned, 0.5 for fixed–fixed, 0.7 for fixed–pinned and 2.0 for a cantilever (fixed–free). The Euler load uses (KL)² in the denominator, so K has a squared effect on capacity.

Question 3

Why does the IPE mode use the weak axis?

Accepted Answer

A column that is not braced differently in the two directions always buckles about the axis with the larger slenderness — for I-shaped sections that is the weak (z) axis with the smaller radius of gyration. If your column is braced about the weak axis, use manual mode with the strong-axis properties.

Question 4

Is the Euler load a safe design value?

Accepted Answer

No. The Euler load is the theoretical elastic limit for a perfect column. Real columns have residual stresses and initial imperfections, which is why the AISC curve reduces capacity — use φPn, not Ncr, for design.

Question 5

Can I use this for other materials?

Accepted Answer

Yes for the Euler part — set E for aluminium, timber, etc. The AISC E3 curve, however, is calibrated for hot-rolled steel; for other materials use the appropriate design standard.

Column Buckling Calculator