HSS18X18X5/8 Steel Rectangular HSS — Section Properties
Dimensions
| Property | Value | Unit |
|---|---|---|
| Height (h) | 18 | 457.2 mm |
| Width (w) | 18 | 457.2 mm |
| Wall Thickness (t) | 0.625 | 15.9 mm |
| Area (A) | 39.6 in² | 255.5 cmÃÂò |
| Weight | 144.4 lb/ft | 214.9 kg/m |
Elastic Section Properties
| Property | Strong Axis (X-X) | Weak Axis (Y-Y) | Unit |
|---|---|---|---|
| Moment of Inertia (I) | 1980 | 1980 | in⁴ |
| Elastic Section Modulus (S) | 220 | 220 | in³ |
| Plastic Section Modulus (Z) | 257 | 257 | in³ |
| Radius of Gyration (r) | 7.07 | 7.07 | in |
Torsional Properties
| Property | Value | Unit |
|---|---|---|
| Torsional Constant (J) | 3120 | in⁴ |
| Warping Constant (Cw) | 0 | in⁶ |
Section Profile Summary
HSS provides uniform strength in all directions — efficient for columns, bracing, and torsion-critical applications. At 144.4 lb/ft, this section is well-suited for bracing, secondary columns, and architectural exposed steel.
Key Design Checks (AISC 360)
| Check | Formula | This Section |
|---|---|---|
| Plastic moment | Mp = Zx × Fy | 12,850 kip-in |
| Deflection | Δ = 5wLâÃÂô/(384EIx) | Use Ix = 1,980 in⁴ |
| Torsion | St. Venant = GJ/L | J = 3,120 in⁴ |
| Column buckling | KL/r âÃÂàFcr | r_x = 7.07 in |
Design Notes
- Wall slenderness: b/t limits per AISC 360 Table B4.1a define compact, noncompact, and slender classifications. Round HSS use D/t limits.
- HSS connection design: Welded connections to HSS walls must check chord plastification, punching shear, and sidewall yielding per AISC 360 Chapter K. Through-bolting requires reinforcing sleeves or plate washers.
- Concrete-filled HSS: For composite column applications, filling the HSS with concrete increases axial capacity and fire resistance. Composite design follows AISC 360 Chapter I.
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: Column Capacity — hss18x18x5-8
Scenario: Braced frame diagonal in an industrial building Unbraced length L = 15 ft.
Given:
- hss18x18x5-8: Ag = 39.6 in²
- r_min = 7.07 in (governing radius of gyration)
- Steel: ASTM A500 Gr. C, Fy = 50 ksi, E = 29,000 ksi
- Effective length factor K = 1.0 (pinned ends)
Step 1 — Slenderness ratio:
KL/r = 180 / 7.07 = 25
Step 2 — Determine critical stress Fcr (AISC 360 Chapter E):
Elastic buckling stress: Fe = ÃÂÃÂÃÂòE / (KL/r)ÃÂò = ÃÂÃÂÃÂò × 29,000 / (25)ÃÂò = 458 ksi
For HSS with KL/r âÃÂä 4.71âÃÂÃÂ(E/Fy) = 4.71âÃÂÃÂ(29,000/50) = 113.4:
If KL/r âÃÂä 113.4: Fcr = 0.658^(Fy/Fe) × Fy (inelastic buckling) If KL/r > 113.4: Fcr = 0.877Fe (elastic buckling)
Step 3 — Design compressive strength:
φPn = φ × Fcr × Ag = 0.9 × Fcr × 39.6 âÃÂà1,782 kips (preliminary)
For a precise capacity accounting for local buckling and the exact KL/r value, use the Column Capacity Calculator with this section's properties.
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.