What is the section modulus of HSS20X12X3/8?

Sx = 120 inÃÂÃÂ³, Zx = 144 inÃÂÃÂ³ (strong axis). Sy = 91.1 inÃÂÃÂ³, Zy = 102 inÃÂÃÂ³ (weak axis).

What steel grade is standard for HSS20X12X3/8?

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

What is the moment of inertia of HSS20X12X3/8?

Ix = 1200 inÃÂ¢ÃÂÃÂ´ about the strong axis and Iy = 547 inÃÂ¢ÃÂÃÂ´ about the weak axis. The radius of gyration is rx = 7.45 in and ry = 5.04 in.

HSS20X12X3/8 Steel Rectangular HSS — Section Properties

Dimensions

Property	Value	Unit
Height (h)	20	508.0 mm
Width (w)	12	304.8 mm
Wall Thickness (t)	0.375	9.5 mm
Area (A)	21.5 in²	138.7 cmÃÂÃÂ²
Weight	78.52 lb/ft	116.9 kg/m

Elastic Section Properties

Property	Strong Axis (X-X)	Weak Axis (Y-Y)	Unit
Moment of Inertia (I)	1200	547	in⁴
Elastic Section Modulus (S)	120	91.1	in³
Plastic Section Modulus (Z)	144	102	in³
Radius of Gyration (r)	7.45	5.04	in

Torsional Properties

Property	Value	Unit
Torsional Constant (J)	1180	in⁴
Warping Constant (Cw)	0	in⁶

Section Profile Summary

Closed tubular section with J = 1,180 in⁴ — torsional stiffness is significantly higher than an open section of equivalent weight. The flat faces accept welded gusset and end-plate connections without stiffeners.

Key Design Checks (AISC 360)

Check	Formula	This Section
Plastic moment	Mp = Zx × Fy	7,200 kip-in
Deflection	Δ = 5wLÃÂ¢ÃÂÃÂ´/(384EIx)	Use Ix = 1,200 in⁴
Torsion	St. Venant = GJ/L	J = 1,180 in⁴
Column buckling	KL/r ÃÂ¢ÃÂÃÂ Fcr	r_x = 7.45 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 — hss20x12x3-8

Scenario: Parking structure column — 2 levels Unbraced length L = 8 ft.

Given:

hss20x12x3-8: Ag = 21.5 in²
r_min = 7.45 in (governing radius of gyration)
Steel: ASTM A500 Gr. C, Fy = 50 ksi, E = 29,000 ksi
Effective length factor K = 1.0 (braced frame)

Step 1 — Slenderness ratio:

KL/r = 96 / 7.45 = 13

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

Elastic buckling stress: Fe = ÃÂÃÂÃÂÃÂ²E / (KL/r)ÃÂÃÂ² = ÃÂÃÂÃÂÃÂ² × 29,000 / (13)ÃÂÃÂ² = 1,694 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 × 21.5 ÃÂ¢ÃÂÃÂ 968 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.