WT20X251.5 Steel WT-shape — Section Properties
Dimensions
| Property | Value | Unit |
|---|---|---|
| Depth (d) | 21 | 533.4 mm |
| Flange Width (bf) | 16.4 | 41.66 cm |
| Flange Thickness (tf) | 2.76 | 70.1 mm |
| Web Thickness (tw) | 1.54 | 39.1 mm |
| Area (A) | 74 in² | 477.4 cmÃÂò |
| Weight | 251.5 lb/ft | 374.3 kg/m |
Elastic Section Properties
| Property | Strong Axis (X-X) | Weak Axis (Y-Y) | Unit |
|---|---|---|---|
| Moment of Inertia (I) | 2730 | 1020 | in⁴ |
| Elastic Section Modulus (S) | 174 | 124 | in³ |
| Plastic Section Modulus (Z) | 314 | 197 | in³ |
| Radius of Gyration (r) | 6.07 | 3.72 | in |
Torsional Properties
| Property | Value | Unit |
|---|---|---|
| Torsional Constant (J) | 138 | in⁴ |
| Warping Constant (Cw) | 1400 | in⁶ |
Section Profile Summary
WT/ST sections are cut from W-shapes — the stem tip was at the mid-depth of the original beam and has the highest residual stresses. For beam applications, orient the stem in tension (pointing down for simply-supported beams). Per AISC 360 Section F9, the flexural capacity depends on whether the stem or flange is in compression.
At 21" deep, this section is frequently specified for primary floor beams, girders, and moment frame columns in commercial and institutional buildings.
Key Design Checks (AISC 360)
| Check | Formula | This Section |
|---|---|---|
| Plastic moment | Mp = Zx × Fy | 15,700 kip-in |
| Deflection | Δ = 5wLâÃÂô/(384EIx) | Use Ix = 2,730 in⁴ |
| Torsion | St. Venant = GJ/L | J = 138 in⁴ |
| Column buckling | KL/r âÃÂàFcr | r_x = 6.07 in |
Design Notes
- Stem in tension for beams: Orient the tee so the flange is in compression (stem down for gravity loads). Per AISC 360 Section F9, the flexural capacity is significantly higher with the stem in tension.
- Flexural-torsional buckling for columns: Single-axis symmetry means the governing buckling mode may be flexural-torsional rather than pure flexural per AISC 360 Eq. E4-4.
- Connection eccentricity: The centroid is closer to the flange — tension connections must account for the induced bending when the work line differs from the centroidal axis.
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 Capacity — wt20x251_5
Scenario: wt20x251_5 used as a bottom chord member in a roof truss. The member carries axial tension only under the governing load combination.
Given:
- wt20x251_5: gross area Ag = 74 in²
- Steel: Fy = 50 ksi, Fu = 65 ksi
- Connection: bolted through the flange with 4 bolts per line (standard holes)
Step 1 — Gross yield (AISC 360 Eq. D2-1):
φTn_yield = 0.9 × Ag × Fy = 0.9 × 74 × 50 = 3,330 kips
Step 2 — Net section fracture:
For bolted connections, deduct bolt holes from Ag: An = Ag − n × dh × tf
The effective net area Ae = U × An depends on the shear lag factor U per AISC 360 Table D3.1.
Check φTn_fracture = 0.75 × Ae × Fu per AISC 360 Eq. D2-2.
Step 3 — Stem-in-tension note:
For WT/ST sections loaded in axial tension, the eccentricity between the centroid and the connection plane introduces a bending moment that should be considered in the connection design. The stem is more flexible than the flange — verify the weld or bolt group can accommodate the induced prying action.
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.