Steel Beam Calculator

AISC 360-22 requires checking: flexural strength (moment capacity), shear strength, lateral-torsional buckling (LTB), local buckling, and deflection limits. Calculate required moment (Mu) and shear (Vu) from loads, then verify beam capacity exceeds demand. Use LRFD (Load and Resistance Factor Design) or ASD (Allowable Stress Design) methods.

LTB occurs when a beam's compression flange buckles sideways and twists. It's controlled by unbraced length (Lb), beam geometry, and moment gradient. AISC provides three design cases: plastic (compact), inelastic, and elastic buckling. Reduce unbraced length with lateral bracing, use deeper sections, or select sections with higher LTB capacity. The calculator determines LTB capacity based on these factors.

Moment capacity (Mn) depends on: section properties (Zx, Sx), yield strength (Fy), unbraced length, and LTB. For compact sections with adequate bracing: Mn = Fy × Zx. For LTB-controlled sections: Mn = Fcr × Sx, where Fcr is buckling stress from AISC equations. The calculator handles all cases per AISC 360-22 Chapter F.

Plastic sections: Can develop full plastic moment (Mp) and rotate significantly. Compact sections: Can develop Mp but limited rotation. Non-compact: Cannot develop Mp, limited by local buckling. Slender: Local buckling controls before yield. AISC classifies sections by width-to-thickness ratios (λ). Compact sections (λ ≤ λp) are most efficient for flexure.

Shear capacity (Vn) = 0.6 × Fy × Aw × Cv, where Aw is web area and Cv is web shear coefficient. For unstiffened webs: Cv = 1.0 if h/tw ≤ 2.24√(E/Fy), otherwise reduced per AISC G2. Stiffened webs allow higher Cv. Check Vu ≤ φVn (LRFD) or Va ≤ Vn/Ω (ASD). Most wide-flange beams are shear-governed by web area, not buckling.

Common deflection limits: L/360 for live loads (floors), L/240 for total loads, L/300 for roofs, L/180 for plastered ceilings. L is span length. More restrictive limits improve serviceability but may require larger sections. The calculator checks deflection against user-specified limits and calculates required moment of inertia (Ix).

Compare weight per foot (lb/ft) for sections meeting all requirements. Lightest section is usually most economical. Consider: fabrication costs (standard sizes cheaper), availability, depth constraints, and connection requirements. Use AISC Steel Construction Manual beam selection tables or the calculator's optimization feature to find minimum weight solutions.