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The HSS steel's specified minimum yield strength.
Commonly 345 MPa (50 ksi) for Grade B/C HSS.
The hollow steel section's own cross-sectional (wall) area, from the manufacturer's tables.
The steel area from the shape table, not calculated from the outside dimensions and the nominal wall. HSS corners are radiused and the wall is thinner than nominal by the manufacturing tolerance, so a hand calculation over-states the steel by several per cent — which is the unconservative direction in a composite column where the steel does most of the work.
The HSS shape, which sets the concrete confinement coefficient C2.
Round HSS confines the concrete infill more effectively than rectangular/square HSS, so AISC assigns it a higher C2 coefficient.
The specified compressive strength of the concrete infill.
Commonly 30 MPa (4,350 psi) for a filled HSS column.
The cross-sectional area of the concrete infill (inside the HSS wall).
The area inside the wall, which is the outside dimensions less twice the DESIGN wall thickness, and the corners are radiused there too. Reinforcement inside the infill displaces concrete and has its own contribution that this arrangement does not carry. An infill that is not fully placed — a void at the top of a lift — is not the area entered here, and is the commonest defect in a filled tube.
Cross-sectional compressive capacity Pno
617 kips
This is the zero-length NOMINAL cross-sectional capacity (Pno) for a compact section. TWO steps stand between it and a design strength you may compare against a factored load: the AISC slenderness reduction (Pn = Pno x 0.658^(Pno/Pe), from the effective stiffness and unbraced length), and the resistance factor phi_c = 0.75 from AISC 360 I2.2b. Neither is applied above. A short, well-braced column is the dangerous case here, because the slenderness step barely moves it and the missing phi alone leaves a third more capacity than the code allows. Consult a structural engineer for final column design.
- phi_c x Pno (phi_c = 0.75, still before slenderness)
- 462.83 kips
They open the calculator with your figures already in it
Concrete-Filled HSS Composite Column Capacity Calculator: 617 kips — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- AISC 360 Chapter I (§I1.2a, §I2.2b): Pno = Fy×As + C2×f'c×Ac, where C2 = 0.85 for rectangular HSS and 0.95 for round HSS (confinement effect)
Inputs used
- Steel Yield Strength Fy
- 50038.02 psi
- Steel HSS Cross-Sectional Area As
- 7.75 in²
- HSS Shape
- Rectangular/Square HSS (C2 = 0.85)
- Concrete Strength f'c
- 4351.13 psi
- Concrete Infill Area Ac
- 62 in²
Intermediate steps
- phi_c x Pno (phi_c = 0.75, still before slenderness)
- 462.83 kips
Confidence note: This is the zero-length NOMINAL cross-sectional capacity (Pno) for a compact section. TWO steps stand between it and a design strength you may compare against a factored load: the AISC slenderness reduction (Pn = Pno x 0.658^(Pno/Pe), from the effective stiffness and unbraced length), and the resistance factor phi_c = 0.75 from AISC 360 I2.2b. Neither is applied above. A short, well-braced column is the dangerous case here, because the slenderness step barely moves it and the missing phi alone leaves a third more capacity than the code allows. Consult a structural engineer for final column design.
What this calculation does not cover
- The equation above is the compact-section case only. AISC classifies a filled section by wall slenderness — b/t against 2.26√(E/Fy) for rectangular HSS, D/t against 0.15E/Fy for round — and a noncompact or slender wall buckles locally before the steel ever reaches Fy, so Pno then comes from a different and lower expression. Fy × As applied to a thin-walled tube overstates the steel's contribution, not the concrete's, and nothing on this page checks the wall.
- The concrete only carries its share if the load is actually put into it. Where a beam or cap plate delivers load to the steel tube alone, AISC Chapter I6 governs the transfer into the core — direct bearing, limited to 1.7 f'c on the bearing area, or shear connectors inside the tube — and it has to occur within the load introduction length either side of the connection. A column detailed to bear on the tube wall alone never develops the Ac term counted above.
- This is the room-temperature capacity. A concrete-filled HSS is often chosen for its fire performance, where the tube weakens first and the core carries the column — which usually means reinforcing bar or fiber in the fill, and always means vent holes drilled through the tube wall at each floor, because steam trapped in a heated sealed tube can burst it. None of that follows from Pno.
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This result is a specification — 617 kips — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- AISC 360 Chapter I (§I1.2a, §I2.2b): Pno = Fy×As + C2×f'c×Ac, where C2 = 0.85 for rectangular HSS and 0.95 for round HSS (confinement effect)
Which documents these citations point at
Standards referenced: AISC 360 (American Institute of Steel Construction, United States).
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