Equal-Leg Angle Properties — AISC (A36 / A572 Gr50)

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Designation: L B × B × t (e.g., L4×4×1/2 = 4 in legs, 1/2 in thickness)

Selected Unequal-Leg Angles — Common Sizes

Designation: L B × b × t (longer leg first, e.g., L5×3×3/8)

Minimum Fillet Weld Size for Angles

When welding angles to gussets or base plates, minimum weld size per AISC Table J2.4 depends on the angle leg thickness:

Common Angle Applications

Slenderness Limits for Compression

Per AISC Table B4.1a (compression in angles):

For equal-leg angles as compression members:
  λ = b/t (outstanding leg to thickness)
  λp (compact) = 0.54√(E/Fy) = 13.0 (Fy = 50 ksi)
  λr (non-compact/slender boundary) = 0.91√(E/Fy) = 21.9

For b/t > 21.9: angle leg is slender — reduced compression capacity

Common angle b/t ratios:

Metric Angle Sizes (AS/NZS 3679.1)

Frequently Asked Questions

What is the most common structural angle size? L4×4×3/8 and L6×6×1/2 are among the most frequently used. For light framing and bracing, L3×3×3/16 to L4×4×1/4 are typical. For ledger angles supporting masonry veneer, L4×4×3/8 to L5×5×1/2 are most common.

Are equal-leg or unequal-leg angles better for bracing? Equal-leg angles are preferred for single-angle bracing because they can be connected through one leg and achieve balanced stiffness about both axes. Unequal-leg angles are used when specific geometric constraints require one longer leg (e.g., connecting to a web vs. flange of different depths).

How do I calculate the axial capacity of an angle brace? Per AISC 360-22 Chapter E: φPn = φ × Fcr × A, where Fcr is determined from KL/r (using the minor principal axis for single angles connected one leg). AISC 360 Section E5 applies for single angles. KL/r must include modification for eccentricity in single-angle members connected through one leg.

What is the rz radius of gyration? rz is the radius of gyration about the minor principal axis (the diagonal axis through the angle at 45° from the legs). For equal-leg angles, rz is the minimum r and governs weak-axis buckling. It is always smaller than rx = ry. For L4×4×1/2: rz = 0.617 in vs. rx = 1.22 in — rz governs for compression.

When do you use equal-leg versus unequal-leg angles in structural applications? Equal-leg angles are preferred when the connection can be made symmetrically through one leg or when the member needs comparable stiffness about both principal axes, such as in X-brace diagonals and lightly loaded compression members. Unequal-leg angles are used when geometric constraints favor one longer leg — for example, connecting to a beam web while spanning a larger depth, supporting masonry ledgers where the horizontal leg must extend further, or achieving a specific eccentricity in a framing angle connection. For most bracing and light framing applications, equal-leg angles simplify connection design because the centroid is equidistant from both legs.

How do you calculate the weak-axis radius of gyration for an angle used as a brace? For a single angle connected through one leg, the governing slenderness uses rz, the radius of gyration about the minor principal axis (the z-axis at approximately 45° to the legs). For equal-leg angles, rz ≈ 0.195 × b where b is the leg width in inches, though exact values should be taken from AISC tables. AISC 360-22 Section E5 applies additional modifiers for single-angle members to account for the eccentricity of the end connection; the effective slenderness is taken as KL/rz but with KL/r not less than 0.5×(KL/rx) to limit the reduction for closely spaced connections. For an L4×4×3/8 brace at 10 ft (KL = 120 in): KL/rz = 120/0.622 ≈ 193, close to the AISC recommended limit of 200 for bracing members.

What ASTM grade is typically specified for structural steel angles? The most common specifications are ASTM A36 (Fy = 36 ksi, Fu = 58 ksi) and ASTM A572 Grade 50 (Fy = 50 ksi, Fu = 65 ksi). A36 has historically been the default for angles because it is widely available and its lower yield strength can be advantageous for connection ductility. A572 Gr50 is increasingly specified to reduce section sizes and weight, particularly for longer bracing members where higher Fy improves compression capacity. ASTM A529 Grade 50 and A709 Grade 50 are sometimes used for bridge applications. Mill-produced angles in the US are predominantly dual-certified to both A36 and A572 Gr50, so the engineer of record should verify certification with the fabricator before assuming Fy = 50 ksi for design.

Run This Calculation

→ Beam Capacity Calculator — bending and shear capacity for steel angle sections used as beams or lintels.

→ Section Properties Calculator — Ix, Iy, Iz, rx, ry, rz, and centroid location for any angle size in this table.

Try it now: Check your steel angle sizes with our free Steel Weight calculator →

Related pages

• Column Axial Load Design Check — single angle compression capacity with KL/r check
• Steel Section Types — angles vs. HSS vs. W-shapes for specific applications
• Fillet Weld Size Chart — weld sizes for connecting angles to gussets
• Bolt Hole Sizes Reference — hole sizes for angle bolted connections
• HSS Section Properties — alternative tubular sections for compression members
• Reference tables directory
• How to verify calculator results
• structural steel weight per foot table
• Steel Channel Sizes
• Wide Flange Beam Sizes
• steel member weight calculator

Section properties from AISC Steel Construction Manual 16th Ed., Part 1. Area (A), moments of inertia (I), and section moduli (S) calculated about axes through the centroid. For connection design, always account for eccentricity of load relative to bolt group centroid.

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