What is the properties of steel?

The principal engineering properties of structural steel are: yield strength (Fy = 36–80 ksi depending on grade), ultimate tensile strength (Fu = 58–100 ksi), elastic modulus (E = 29 000 ksi / 200 GPa, essentially constant for all grades), elongation at break (18–23 %), Poisson's ratio (ν = 0.30), density (7 850 kg/m³), thermal expansion (α = 11.7 × 10⁻⁶ /°C), and weldability measured by carbon equivalent. Combined, these give steel its predictable, ductile behavior under load.

Why is steel so strong?

Steel is strong because adding 0.05–2.0 % carbon to iron creates iron-carbide (Fe₃C) particles that obstruct dislocation motion through the crystal lattice. Heat treatment, alloying elements (Mn, Cr, Mo, V, Ni), and cold-working amplify that obstruction further — modern HSLA steels reach 70–100 ksi yield. The combination of metallic bonding, body-centered-cubic crystal structure, and engineered impurities gives steel its rare combination of high strength and high ductility.

What is the yield strength of HSS steel?

For ASTM A500 Grade C — the dominant North American HSS grade — the yield strength is Fy = 50 ksi (345 MPa) for rectangular and square sections, and Fy = 46 ksi (315 MPa) for round sections. For ASTM A1085 (preferred for seismic detailing), Fy is a controlled 50 ksi minimum with 70 ksi maximum, and Fu = 65 ksi minimum.

What is the difference between A500 and A1085 HSS?

A500 has historically allowed wider variation in wall thickness and yield strength, with no upper limit on Fy and a wall-thickness tolerance of −10 %. A1085 (introduced 2013) uses 100 % nominal wall thickness in design, caps Fy at 70 ksi, requires CVN toughness when specified, and runs slightly tighter chemistry. For high-seismic and impact-rated work, specify A1085.

How is high-strength steel different from mild steel?

Mild steel (A36) has Fy = 36 ksi and Fu = 58 ksi — driven by carbon content alone. High-strength steels (A572 Gr. 50, A992, A913, A1085) hit Fy = 50–80 ksi by adding micro-alloys (Nb, V, Ti) and using controlled rolling instead of more carbon. The result: same ductility, higher strength, lighter members. Ultra-high-strength alloys (A514, A709 HPS-100W) reach Fy = 100 ksi for bridge and crane work.

What is the properties of steel?

The principal engineering properties of structural steel are: yield strength (Fy = 36–80 ksi depending on grade), ultimate tensile strength (Fu = 58–100 ksi), elastic modulus (E = 29 000 ksi / 200 GPa, essentially constant for all grades), elongation at break (18–23 %), Poisson's ratio (ν = 0.30), density (7 850 kg/m³), thermal expansion (α = 11.7 × 10⁻⁶ /°C), and weldability measured by carbon equivalent. Combined, these give steel its predictable, ductile behavior under load.

Why is steel so strong?

Steel is strong because adding 0.05–2.0 % carbon to iron creates iron-carbide (Fe₃C) particles that obstruct dislocation motion through the crystal lattice. Heat treatment, alloying elements (Mn, Cr, Mo, V, Ni), and cold-working amplify that obstruction further — modern HSLA steels reach 70–100 ksi yield. The combination of metallic bonding, body-centered-cubic crystal structure, and engineered impurities gives steel its rare combination of high strength and high ductility.

What is the yield strength of HSS steel?

For ASTM A500 Grade C — the dominant North American HSS grade — the yield strength is Fy = 50 ksi (345 MPa) for rectangular and square sections, and Fy = 46 ksi (315 MPa) for round sections. For ASTM A1085 (preferred for seismic detailing), Fy is a controlled 50 ksi minimum with 70 ksi maximum, and Fu = 65 ksi minimum.

What is the difference between A500 and A1085 HSS?

A500 has historically allowed wider variation in wall thickness and yield strength, with no upper limit on Fy and a wall-thickness tolerance of −10 %. A1085 (introduced 2013) uses 100 % nominal wall thickness in design, caps Fy at 70 ksi, requires CVN toughness when specified, and runs slightly tighter chemistry. For high-seismic and impact-rated work, specify A1085.

How is high-strength steel different from mild steel?

Mild steel (A36) has Fy = 36 ksi and Fu = 58 ksi — driven by carbon content alone. High-strength steels (A572 Gr. 50, A992, A913, A1085) hit Fy = 50–80 ksi by adding micro-alloys (Nb, V, Ti) and using controlled rolling instead of more carbon. The result: same ductility, higher strength, lighter members. Ultra-high-strength alloys (A514, A709 HPS-100W) reach Fy = 100 ksi for bridge and crane work.

Reference · Material specs

HSS Steel Material — Yield Strength, UTS & Grade Reference

HSS steel material — hollow structural sections per ASTM A500 Grade C — has a yield strength of 50 ksi (rectangular) or 46 ksi (round) and an ultimate tensile strength of 62 ksi. This page covers the mechanical properties of structural steel grades, why steel is strong, the difference between mild and high-strength alloys, and a worked HSS column design example. Reviewed by a licensed PE.

What HSS steel material is

Steel is an iron–carbon alloy (0.05–2.0 % C) with engineered amounts of Mn, Si, Cr, Ni, Mo, and micro-alloys that give it predictable strength and ductility. "HSS steel material" specifically refers to hollow structural sections — square, rectangular, and round closed tubes used for columns, braces, trusses, and architecturally exposed framing.

In North America, HSS is governed by ASTM A500 (cold-formed) or A1085 (cold-formed with tighter tolerances). Both are listed in AISC 360 as permitted structural materials. Because closed sections resist torsion and compression efficiently, HSS is the default choice when a designer needs high stiffness with a low painted/exposed surface area.

Stress, strain, and design strength formulas

Eq. 01 — Yield strength definition SI

F_y = \frac{P_{yield}}{A_g}

·: F_y = Yield strength (0.2 % offset), ksi
·: P_yield = Tensile force at 0.2 % permanent strain, kip
·: A_g = Original gross cross-section area, in²

Eq. 02 — Hooke's law (elastic region) SI

\sigma = E \cdot \varepsilon

·: σ = Stress, ksi
·: E = Modulus of elasticity = 29 000, ksi
·: ε = Engineering strain (dimensionless)

Eq. 03 — LRFD tension design strength SI

\phi P_n = \phi \cdot F_y \cdot A_g

·: φ = Resistance factor for yielding = 0.90
·: P_n = Nominal tension strength, kip
·: F_y = Specified minimum yield strength, ksi
·: A_g = Gross cross-section area, in²

Standards governing structural steel

Standard	Scope	Fy (ksi)	Fu (ksi)
ASTM A36	Carbon mild plate / shapes	36	58–80
ASTM A572 Gr. 50	HSLA plate / shapes	50	65
ASTM A992	Wide-flange (W-shape) standard	50–65	65 min
ASTM A500 Gr. C — rect.	HSS cold-formed rectangular	50	62
ASTM A500 Gr. C — round	HSS cold-formed round	46	62
ASTM A1085	HSS — improved tolerances	50–70	65 min
ASTM A913 Gr. 65/70	QST high-strength shapes	65 / 70	80 / 90
ASTM A514	Quenched-tempered ultra-high strength	100	110

Reference values — properties of structural steel

Property	Value	Notes
Modulus of elasticity, E	29 000 ksi (200 GPa)	Same for every grade
Shear modulus, G	11 200 ksi (77 GPa)	From E and ν
Poisson's ratio, ν	0.30	Elastic, all grades
Density, ρ	7 850 kg/m³ (490 lb/ft³)	490 plf for unit-volume estimates
Coefficient of thermal expansion, α	11.7 × 10⁻⁶ /°C (6.5 × 10⁻⁶ /°F)	Used in PEMB and bridge expansion design
Specific heat	0.49 kJ/(kg·K)	Ambient temperature
Thermal conductivity	50 W/(m·K) at 20 °C	Drops with temp
Elongation at break	18–23 % in 8 in (200 mm)	Per ASTM tensile spec

Identify the steel grade Read the mill certificate or the structural drawing key plan: A500 Grade C, A992, A572 Gr. 50, A36, etc. Each grade pins both Fy (yield) and Fu (ultimate) per the ASTM spec.
Look up Fy and Fu For A500 Grade C HSS round: Fy = 46 ksi, Fu = 62 ksi. For A500 Grade C HSS rectangular: Fy = 50 ksi. For A992 W-shapes: Fy = 50 ksi, Fu = 65 ksi.
Compute design strength For LRFD (AISC 360, Chapter D): φPn = φ · Fy · Ag with φ = 0.90 for tension yielding. For ASD: Pa = Fy · Ag / Ω with Ω = 1.67.
Check elongation and ductility Most structural steels guarantee 18–23 % elongation in 8 in (200 mm). For seismic / SCBF, switch to A500 Grade C HSS or A1085 (tighter chemistry, better toughness).
Verify weldability and chemistry Confirm CE (carbon equivalent) is below 0.45 for non-preheat weldability; for high-strength A913 Gr. 65/70/80, follow AWS D1.1 preheat tables.

Worked example — HSS6×6×3/8 column at 100 kip axial

Specify an HSS6×6×3/8 (A500 Gr. C, Fy = 50 ksi) column with KL = 12 ft and verify it carries 100 kip axial compression.

Section properties: Ag = 7.58 in², rx = ry = 2.34 in.
Slenderness: KL/r = 12 × 12 / 2.34 = 61.5 → inelastic Euler region.
Elastic stress: Fe = π² · 29 000 / 61.5² = 75.6 ksi.
Critical stress: Fcr = (0.658^(50/75.6)) · 50 = 38.0 ksi (AISC E3-2).
Nominal strength: Pn = 38.0 × 7.58 = 288 kip.
LRFD capacity: φPn = 0.90 × 288 = 259 kip > 1.6 × 100 = 160 kip.

Comparison — HSS A500 vs. A1085 vs. wide-flange A992

Aspect	HSS A500 Gr. C	HSS A1085	W-shape A992
Form	Closed tube	Closed tube	Open I
Fy (ksi)	50 / 46	50 (controlled max 70)	50
Wall thickness in design	0.93 × t (NEC reduction)	1.00 × t (full nominal)	n/a
CVN toughness	Not required	Optional supplement	Not required
Best for	General framing, AESS	Seismic SCBF, impact	Beams, columns, moment frames
Cost premium vs. A36 plate	~5–10 %	~10–15 %	baseline rolled shape

HSS steel material in context — related queries

High strength steel and high strength steel alloys

High-strength steel covers any structural grade with Fy ≥ 50 ksi (345 MPa). The dominant family — HSLA (high-strength low-alloy) — uses controlled rolling and trace additions of niobium, vanadium, and titanium to refine the grain structure rather than packing in more carbon. ASTM A572 Gr. 50, A913 Gr. 65/70, and A1011 SS Gr. 50 sit in this family. Ultra-high-strength alloys like A514 push to Fy = 100 ksi and A1066 to 80 ksi for crane runway, mining, and military applications.

Steel column and column base plate design

Steel columns are dimensioned by axial load, end fixity, and unbraced length. AISC E3 governs the inelastic and elastic Euler buckling regimes. The base plate at the foundation interface is sized per AISC Design Guide 1, balancing bearing stress on the concrete pier against bending in the plate itself. For HSS columns, weld a cap plate with full-penetration groove welds and anchor with at least four bolts to handle shear plus uplift.

Steel beam and steel beam span rule of thumb

For preliminary sizing, a quick rule of thumb gives a wide-flange beam depth of about L/20 (in inches) for typical office floor loads, where L is the span in feet. A 30 ft span needs roughly an 18 in deep W-shape (W18×35 to W18×50, depending on tributary width). Final design uses AISC F2 for compact bending and L/360 / L/240 deflection limits per IBC 1604.3.

Steel plate and steel plate bearing

Steel plate (A36, A572 Gr. 50, A1011) is sold in 1/4" to 6" thicknesses for connections, base plates, gussets, and stiffeners. Bearing stress at bolt holes is governed by AISC J3.10: ϕRn = 1.2 · Lc · t · Fu, with the deformation limit usually controlling.

Steel structure, steel frame and bracing

A steel structure or steel frame combines columns, beams, and lateral bracing into one load path. Braced steel frames (X-, K-, V-, eccentric brace) resist lateral loads through axial member force, while moment frames rely on rigid beam-to-column joints. For seismic SCBF (special concentrically braced frames), AISC 341 requires HSS A500 Gr. C or A1085 with KL/r ≤ 200, compact b/t, and CVN-tested welds.

What is the properties of steel?: The principal engineering properties of structural steel are: yield strength (Fy = 36–80 ksi depending on grade), ultimate tensile strength (Fu = 58–100 ksi), elastic modulus (E = 29 000 ksi / 200 GPa, essentially constant for all grades), elongation at break (18–23 %), Poisson's ratio (ν = 0.30), density (7 850 kg/m³), thermal expansion (α = 11.7 × 10⁻⁶ /°C), and weldability measured by carbon equivalent. Combined, these give steel its predictable, ductile behavior under load.
Why is steel so strong?: Steel is strong because adding 0.05–2.0 % carbon to iron creates iron-carbide (Fe₃C) particles that obstruct dislocation motion through the crystal lattice. Heat treatment, alloying elements (Mn, Cr, Mo, V, Ni), and cold-working amplify that obstruction further — modern HSLA steels reach 70–100 ksi yield. The combination of metallic bonding, body-centered-cubic crystal structure, and engineered impurities gives steel its rare combination of high strength and high ductility.
What is the yield strength of HSS steel?: For ASTM A500 Grade C — the dominant North American HSS grade — the yield strength is Fy = 50 ksi (345 MPa) for rectangular and square sections, and Fy = 46 ksi (315 MPa) for round sections. For ASTM A1085 (preferred for seismic detailing), Fy is a controlled 50 ksi minimum with 70 ksi maximum, and Fu = 65 ksi minimum.
What is the difference between A500 and A1085 HSS?: A500 has historically allowed wider variation in wall thickness and yield strength, with no upper limit on Fy and a wall-thickness tolerance of −10 %. A1085 (introduced 2013) uses 100 % nominal wall thickness in design, caps Fy at 70 ksi, requires CVN toughness when specified, and runs slightly tighter chemistry. For high-seismic and impact-rated work, specify A1085.
How is high-strength steel different from mild steel?: Mild steel (A36) has Fy = 36 ksi and Fu = 58 ksi — driven by carbon content alone. High-strength steels (A572 Gr. 50, A992, A913, A1085) hit Fy = 50–80 ksi by adding micro-alloys (Nb, V, Ti) and using controlled rolling instead of more carbon. The result: same ductility, higher strength, lighter members. Ultra-high-strength alloys (A514, A709 HPS-100W) reach Fy = 100 ksi for bridge and crane work.

Regardless of the specified yield strength, the modulus of elasticity of all structural steel grades is taken as 29 000 ksi (200 000 MPa) and Poisson's ratio as 0.30. Designers should specify the lightest member that satisfies strength, serviceability, and fabrication requirements.

AISC Steel Construction Manual, 16th edition → Part 1, General Properties

Sources

AISC 360-22 — Specification for Structural Steel Buildings.
AISC Steel Construction Manual, 16th edition.
AISC 341-22 — Seismic Provisions for Structural Steel Buildings.
ASTM A500 / A1085 — Cold-formed welded HSS specifications.
ASTM A992 / A572 / A913 — Structural shapes specifications.
AWS D1.1 — Structural Welding Code, Steel.