What is the section modulus of HSS20X12X5/8?

Sx = 188 inÃÂÃÂ³, Zx = 230 inÃÂÃÂ³ (strong axis). Sy = 142 inÃÂÃÂ³, Zy = 162 inÃÂÃÂ³ (weak axis).

What steel grade is standard for HSS20X12X5/8?

ASTM A500 Grade C (Fy = 50 ksi) or Grade B (Fy = 46 ksi). Verify with mill certificate.

What is the moment of inertia of HSS20X12X5/8?

Ix = 1880 inÃÂ¢ÃÂÃÂ´ about the strong axis and Iy = 851 inÃÂ¢ÃÂÃÂ´ about the weak axis. The radius of gyration is rx = 7.33 in and ry = 4.93 in.

HSS20X12X5/8 Steel Rectangular HSS — Section Properties

Dimensions

Property	Value	Unit
Height (h)	20	508.0 mm
Width (w)	12	304.8 mm
Wall Thickness (t)	0.625	15.9 mm
Area (A)	35 in²	225.8 cmÃÂÃÂ²
Weight	127.4 lb/ft	189.6 kg/m

Elastic Section Properties

Property	Strong Axis (X-X)	Weak Axis (Y-Y)	Unit
Moment of Inertia (I)	1880	851	in⁴
Elastic Section Modulus (S)	188	142	in³
Plastic Section Modulus (Z)	230	162	in³
Radius of Gyration (r)	7.33	4.93	in

Torsional Properties

Property	Value	Unit
Torsional Constant (J)	1890	in⁴
Warping Constant (Cw)	0	in⁶

Section Profile Summary

The closed shape eliminates the weak-axis buckling concern that governs open sections. Torsional constant J = 1,890 in⁴ is typically an order of magnitude higher than a W-shape of similar weight, making HSS the go-to choice when torsion cannot be avoided.

Key Design Checks (AISC 360)

Check	Formula	This Section
Plastic moment	Mp = Zx × Fy	11,500 kip-in
Deflection	Δ = 5wLÃÂ¢ÃÂÃÂ´/(384EIx)	Use Ix = 1,880 in⁴
Torsion	St. Venant = GJ/L	J = 1,890 in⁴
Column buckling	KL/r ÃÂ¢ÃÂÃÂ Fcr	r_x = 7.33 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 — hss20x12x5-8

Scenario: Braced frame diagonal in an industrial building Unbraced length L = 15 ft.

Given:

hss20x12x5-8: Ag = 35 in²
r_min = 7.33 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 / 7.33 = 25

Step 2 — Determine critical stress Fcr (AISC 360 Chapter E):

Elastic buckling stress: Fe = ÃÂÃÂÃÂÃÂ²E / (KL/r)ÃÂÃÂ² = ÃÂÃÂÃÂÃÂ² × 29,000 / (25)ÃÂÃÂ² = 458 ksi

For HSS with KL/r ÃÂ¢ÃÂÃÂ¤ 4.71ÃÂ¢ÃÂÃÂ(E/Fy) = 4.71ÃÂ¢ÃÂÃÂ(29,000/50) = 113.4:

If KL/r ÃÂ¢ÃÂÃÂ¤ 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 × 35 ÃÂ¢ÃÂÃÂ 1,575 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

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.