Steel Member (Design Only - ASD)

How it calculates

The Steel Member (Design Only - ASD) calculator checks a single member to AISC 360-22 using Allowable Strength Design. Each limit state compares your ASD design force with the nominal strength divided by its Omega safety factor.

ASD safety factors

For flexure Omega_b = 1.67 and for compression Omega_c = 1.67. For shear, Omega_v = 1.50 for rolled W, M and S shapes with h/tw below 2.24√(E/Fy), and 1.67 otherwise. For tension, rupture uses Omega_t = 2.00 and yielding uses Omega_t = 1.67. All check ratios are the design force divided by the allowable strength.

Section classification

Plate element slenderness ratios are compared to the limits from AISC 360-22 Table B4.1a and B4.1b to classify elements as compact, noncompact or slender. If either element is slender in compression, an effective area Ae is used for compression. For square and rectangular HSS with slender flanges, an effective section modulus is used in flexure.

Flexural capacity and lateral-torsional buckling

Chapter F provisions determine Mn. The plastic moment Mp sets the upper bound, and flange and web local buckling can reduce it. LTB reduces capacity when Lb exceeds Lp. The boundary conditions are:

• Lb ≤ Lp: no LTB, Mn = Mp
• Lp < Lb ≤ Lr: linearly reduced by LTB
• Lb > Lr: elastic LTB, Mn = Fcr × Sx

You enter Cb, the moment modification factor, which defaults to 1.0. It is not calculated from the moment diagram. Square and rectangular HSS use their own local buckling and lateral-torsional buckling equations. The strong-axis design moment is the larger of the positive and negative moments you enter.

Compression and column buckling

Chapter E covers flexural buckling about strong and weak axes, plus torsional or flexural-torsional buckling. The critical stress Fcr is derived from the governing slenderness ratio KL/r. The ASD allowable compression capacity is:

Pc = Pn / Omega_c = Fcr × Ag / 1.67

For slender element sections, an effective area Ae reduces Pn. Flexural-torsional buckling uses the singly symmetric equation for channels, and doubly symmetric shapes use the torsional buckling equation.

Tension

Tensile rupture is checked on the effective net area, An × U, where An is the gross area less your hole area. U is calculated from the connection length for HSS, defaults to 0.7 for other shapes, and can be overridden. Tensile yielding sets the axial term in the tension and bending interaction. Slenderness is flagged above 300 for tension members and above 200 otherwise.

Combined actions interaction

Chapter H ASD interaction equations are the key output. For Pa/Pc ≥ 0.2:

interaction ratio = Pa/Pc + (8/9)(Max/Mcx + May/Mcy) ≤ 1.0

For Pa/Pc < 0.2:

interaction ratio = Pa/(2Pc) + (Max/Mcx + May/Mcy) ≤ 1.0

Available flexural strength Mcx includes LTB reductions where applicable. Both required and available strengths are shown for each term, and the interaction cites AISC 360-22 H1.1. The same pair of equations is applied separately to tension with bending.

P-delta and stability

By default, a first-order moment amplifier B1 is applied about each axis to account for P-little delta effects within the member. You enter Cm for each axis, and you can switch amplification off. The member is assumed to be part of a braced frame. Frame-level second-order effects should be addressed before applying this calculator to sway-sensitive structures.

Shear

Strong-axis shear on I-shapes and channels uses the web shear coefficient Cv1, assuming an unstiffened web. Square and rectangular HSS use Cv2, and weak-axis shear also uses Cv2. The allowable shear is Vn / Omega_v, with Omega_v as set out above.