Steel Beam (ASD)

How it calculates

The Steel Beam (ASD, AISC 360-22) calculator runs an allowable strength and deflection check per AISC 360-22 on hot-rolled steel beams with any number of spans and loads.

Section classification (AISC 360-22 B4)

Flanges and webs are classified as compact, noncompact, or slender by comparing width-to-thickness ratios to lambda_p and lambda_r limits. Classification decides whether the full plastic moment is available or a local buckling reduction applies.

Flexural capacity - AISC 360-22 Chapter F

Allowable bending strength is Mn / Omega_b, where Omega_b = 1.67. Positive and negative bending are evaluated separately. utilization = M_a / (Mn / 1.67) ≤ 1.0. For a section with no local buckling or LTB reduction, Mn is the plastic moment Mp. Lateral-torsional buckling is checked with the unbraced length Lb against limiting lengths Lp and Lr. The Cb moment gradient factor accounts for moment variation along the unbraced length. Flange local buckling reductions apply to noncompact and slender flanges. Web local buckling is checked for HSS.

Shear capacity - AISC 360-22 Chapter G

Allowable shear strength is Vn / Omega_v, with Vn = 0.6 Fy Aw Cv. For W, M and S shapes bent about the strong axis with h/tw below 2.24 sqrt(E/Fy), Cv1 = 1.0 and Omega_v = 1.50. Other I-shapes and channels bent about the strong axis use Cv1 from web slenderness with Omega_v = 1.67. HSS, tees, angles and weak-axis bending use Cv2 with Omega_v = 1.67.

Load combination analysis

The default ASD combinations (D; D + L; D + S; D + 0.75L + 0.75S; D + 0.6W; 0.6D + 0.6W; etc.) are run with FEA. Project settings can change this list. The governing combination for moment and for shear is identified separately. Unfactored load cases feed the deflection checks.

Deflection checks

Three deflection limits are tracked, each checked span by span:

• Instantaneous deflection - from live, roof live, snow and 0.42W cases, compared to the lesser of L/n and an absolute limit (defaults L/360 and 2 in)
• Long-term deflection - checked against its own limit (default L/240) and reported when it is more critical than the instantaneous check
• Simplified DL+(LL or SL) deflection - default combination D + L + Lr, limit L/240 by default

utilization = delta / delta_allow ≤ 1.0 for each criterion. Cantilever limits use twice the cantilever length by default.

Inputs summary

Geometry: section designation, yield strength Fy (ksi), span lengths, support types, incline pitch, tributary spacing. Loads: unfactored dead, live, roof live, snow, and wind loads applied as uniform, partial, point, or moment loads. Design criteria: separate deflection limit inputs for live load, long-term, and simplified combined deflection.

Outputs summary

The summary reports critical moment demand and allowable moment, governing load combination for moment and shear, shear demand and allowable shear, and deflection ratios for all three criteria. Inclined beams also report maximum vertical and horizontal reactions. Reactions are structured for direct load linking to column and footing calculations downstream.