L3X2-1/2X1/4 Steel Angle — Section Properties
Dimensions
| Property | Value | Unit |
|---|---|---|
| Leg Length (leg) | 3 | 7.62 cm |
| Leg Thickness (t) | 0.25 | 0.64 cm |
| Area (A) | 1.32 in² | 8.5 cmÃÂò |
| Weight | 4.5 lb/ft | 6.7 kg/m |
Elastic Section Properties
| Property | Strong Axis (X-X) | Weak Axis (Y-Y) | Unit |
|---|---|---|---|
| Moment of Inertia (I) | 1.16 | 0.734 | in⁴ |
| Elastic Section Modulus (S) | 0.555 | 0.397 | in³ |
| Plastic Section Modulus (Z) | 1 | 0.707 | in³ |
| Radius of Gyration (r) | 0.94 | 0.746 | in |
Torsional Properties
| Property | Value | Unit |
|---|---|---|
| Torsional Constant (J) | 0.03 | in⁴ |
| Warping Constant (Cw) | 0.016 | in⁶ |
Section Profile Summary
Leg local buckling (b/t ratio) and shear lag at bolted connections are the governing limit states for this angle in tension applications. Per AISC 360 Section D3, the effective net area accounts for the eccentricity when connected through one leg only.
Key Design Checks (AISC 360)
| Check | Formula | This Section |
|---|---|---|
| Plastic moment | Mp = Zx × Fy | 50 kip-in |
| Deflection | Δ = 5wLâÃÂô/(384EIx) | Use Ix = 1.16 in⁴ |
| Torsion | St. Venant = GJ/L | J = 0.03 in⁴ |
| Column buckling | KL/r âÃÂàFcr | r_x = 0.94 in |
Design Notes
- Single-angle flexure: Use AISC 360 Section F10. Moments are resolved about the principal axes (w-w and z-z), not the geometric axes. The geometric properties above are tabulated for convenience — transform to principal axes for accurate flexure design.
- Leg slenderness: The outstanding leg b/t ratio controls compactness per AISC 360 Table B4.1a, Case 6 (single angle).
- Shear lag in bolted connections: When only one leg is connected, the effective net area per AISC 360 Section D3 accounts for the eccentricity. For welded connections, U depends on the weld length-to-width ratio.
Verification (AISC 360): All designs using this section must be verified by a licensed Professional Engineer. Before finalizing member selection, check beam-column interaction (P-M), lateral-torsional buckling, serviceability deflections, and all connection limit states. See Engineering Disclaimer.
Worked Example: Tension Member Check — l3x2-1-2x1-4
Scenario: A single angle used as a diagonal tension brace in a braced frame bay. The brace is connected to a gusset plate by welding one leg. Because the connection is eccentric (load applied to one leg only), shear lag reduces the effective net area.
Given:
- l3x2-1-2x1-4: gross area Ag = 1.32 in²
- Steel: Fy = 50 ksi, Fu = 65 ksi
- Connection: welded to one leg only
Step 1 — Gross section yield (AISC 360 Eq. D2-1):
φTn_yield = φ × Ag × Fy = 0.9 × 1.32 × 50 = 59 kips
Step 2 — Net section fracture with shear lag (AISC 360 Eq. D2-2):
For a single angle welded to one leg, the shear lag factor U depends on the connection length and eccentricity. Per AISC 360 Table D3.1, for a single angle with 4+ fasteners per line or equivalent weld length, U = 0.80.
Ae = U × An where An = Ag (no bolt holes for welded connection)
φTn_fracture = φ × Ae × Fu = 0.75 × (0.80 × 1.32) × 65 âÃÂà43 kips
Step 3 — Design check:
The smaller of the two limit states governs: φTn = min(yield, fracture) kips. Ensure the factored axial demand (from wind or seismic load combinations) does not exceed this value. Also verify the gusset plate weld length develops the required force.
Related Resources
- Steel Beam Capacity Calculator
- Column Capacity Calculator
- Beam Deflection Calculator
- Section Properties Calculator
- Steel Grades Reference
- Section Comparison Tool
Design Resources
- Section Properties Lookup — Compare with similar sections
- Steel Beam Sizes Reference — Standard beam dimensions
Educational reference only. Verify all section properties against the current AISC 360 Manual and mill certificates before design. Results are PRELIMINARY — NOT FOR CONSTRUCTION.