A36 Mechanical Properties Table

PRELIMINARY — NOT FOR CONSTRUCTION. All values are minimum specified properties. Actual certified mill test report values typically exceed minimums by 10–25%. Must be independently verified by a licensed Professional Engineer before use in design.

Property Value (Imperial) Value (Metric) Notes
Yield Strength Fy 36 ksi min 250 MPa min For t ≤ 8 in (200 mm)
Tensile Strength Fu 58–80 ksi 400–550 MPa 58 ksi / 400 MPa minimum governs
Fy/Fu Ratio ≤ 0.62 typical ≤ 0.62 typical Lower ratio = better ductility
Elongation (8 in / 200 mm) 20% min 20% min Plates and bars
Elongation (2 in / 50 mm) 23% min 23% min
Modulus of Elasticity E 29,000 ksi 200,000 MPa All structural steels
Shear Modulus G 11,200 ksi 77,000 MPa
Density ρ 490 lb/ft³ 7,850 kg/m³
Poisson's Ratio ν 0.30 0.30
Thermal Expansion α 6.5 × 10⁻⁶ /°F 11.7 × 10⁻⁶ /°C

Thickness Adjustments for Yield Strength

A36 yield strength is calibrated at 36 ksi up to 8 inches thick. For thicker plates:

Plate Thickness Minimum Fy Notes
t ≤ 8 in (200 mm) 36 ksi (250 MPa) Standard range for structural plates
8 in < t ≤ 12 in 32 ksi (220 MPa) Reduced yield for ultra-heavy plates
t > 12 in Consult mill Beyond standard A36 scope

These thickness limits matter when designing thick base plates, heavy gusset plates, and built-up column sections. Always verify the applicable thickness bracket before entering Fy into a capacity equation.

A36 Chemical Composition

A36 is a low-carbon steel with controlled manganese for strength and deoxidation. The specification limits phosphorus and sulfur for toughness and weldability:

Element Maximum Content Effect on Properties
Carbon (C) 0.25–0.29% Primary strength contributor; higher C = higher strength but reduced weldability
Manganese (Mn) 0.80–1.20% Counters sulfur embrittlement; contributes to strength
Phosphorus (P) 0.04% max Controlled to prevent cold shortness
Sulfur (S) 0.05% max Controlled to prevent hot shortness
Silicon (Si) 0.40% max Deoxidation agent; improves strength slightly
Copper (Cu) 0.20% min if specified Corrosion resistance (optional)

Carbon limits vary by product form and thickness:

Carbon Equivalent (CE) for Weldability

The carbon equivalent formula predicts hardenability and cold-cracking susceptibility:

CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15

For typical A36 chemistry, CE falls in the range 0.38–0.42. This is below the commonly cited 0.45 threshold where preheat becomes necessary for most structural welding. CE values below 0.40 are considered readily weldable with standard low-hydrogen electrodes.

AWS D1.1 Preheat Requirements for A36

Per AWS D1.1 Structural Welding Code, preheat is based on base metal thickness and carbon equivalent:

Base Metal Thickness Minimum Preheat Temperature Applicable Condition
t < 3/4 in (19 mm) None required Ambient ≥ 50°F (10°C); low-hydrogen electrode
3/4 in ≤ t ≤ 1-1/2 in (38 mm) 50°F (10°C) min Match base metal temperature
1-1/2 in < t ≤ 2-1/2 in (64 mm) 150°F (65°C)
t > 2-1/2 in (64 mm) 225°F (110°C)

These are minimum requirements. Higher preheat may be specified in the welding procedure specification (WPS) for high-restraint joints, low ambient temperatures, or when welding A36 to higher-strength steel. E7018 low-hydrogen electrodes are standard for A36 structural welding.

Product Forms and Typical Sizes

ASTM A36 covers the following product forms:

Product Form Common Sizes Typical Application
Plates 3/16 in – 4 in thick (5–100 mm) Gusset plates, base plates, connection plates, stiffeners
Structural shapes (S, C, L, WT) Per AISC Manual Secondary framing, bracing, lintels
Round bars 1/4 in – 12 in dia Anchor rods, pins, tie rods
Flat bars 1/8 in × 1/2 in – 8 in × 12 in Tension members, stiffeners, spacers
Square bars 1/2 in – 6 in

Note: AISC recommends A992 for W-shapes. Many mills now produce shapes that are dual-certified to both A36 and A992, meaning they meet the chemistry and tensile requirements of A36 while also meeting the Fy = 50 ksi and Fy/Fu ≤ 0.85 requirements of A992.

A36 vs. Higher-Strength Grades

Grade Fy (ksi) Fu (ksi) Fy/Fu Ratio Cost Relative to A36 Best Application
A36 36 58 ≤ 0.62 Baseline (1.0) Plates, bars, secondary framing
A572 Gr 42 42 60 ~0.70 ~1.03 Moderate strength plates
A572 Gr 50 50 65 ~0.77 ~1.05 Primary structural plates, gusset plates
A992 50 65 ≤ 0.85 ~1.05 W-shapes, seismic applications
A588 50 70 ~0.71 ~1.10 Weathering steel (unpainted bridges)
A514 100 110–130 ~0.83 ~1.50 Heavy plate girders, crane girders

A572 Grade 50 provides 39% higher yield strength at essentially the same fabrication cost. For connection plates determined by tension or compression capacity, switching from A36 to A572 Gr 50 can reduce plate thickness by approximately 28% (governed by sqrt(36/50) ≈ 0.85 for area-based checks). This reduction saves material weight, welding volume, and erection time.

International Equivalents

Standard Grade Fy (MPa) Fu (MPa) Notes
ASTM A36 250 400–550 US reference
EN 10025-2 S275JR 275 410–560 Closest EU match; slightly higher Fy
JIS G3101 SS400 245 400–510 Japanese equivalent
AS/NZS 3679.1 Grade 250 260 410 Australian hot-rolled sections
CSA G40.21 260W 260 410 Canadian structural steel
GB/T 700 Q235B 235 375–500 Chinese equivalent

International equivalents are approximate only. Do not substitute across standards without checking chemical composition, CVN toughness, and certification requirements for the governing project specification.

Design Applications

Plate Elements

A36 plates are specified for elements governed by bearing, bolt bearing, block shear, and tension yielding where the 36 ksi strength is not a limiting factor. Common examples:

Tension Members

For A36 tension members, two limit states govern:

  1. Tensile yielding (gross section): φPn = φ × Fy × Ag = 0.90 × 36 ksi × Ag = 32.4 ksi × Ag
  2. Tensile rupture (net section): φPn = φ × Fu × Ae = 0.75 × 58 ksi × Ae = 43.5 ksi × Ae

The governing capacity is the lower of the two. For most practical net sections (Ae/Ag > 0.75), tensile yielding controls.

Welded Connections

For A36 base metal in fillet-welded connections:

Worked Example: A36 Gusset Plate Capacity

Given: A36 gusset plate, 3/8 in × 8 in, with single row of 2 bolts (3/4 in dia, standard holes).

Step 1 — Gross section yielding: φPn = 0.90 × 36 ksi × (3/8 × 8.0) = 0.90 × 36 × 3.0 = 97.2 kips

Step 2 — Net section rupture: Net width = 8.0 − 2 × (3/4 + 1/16) = 8.0 − 1.625 = 6.375 in Ae = 3/8 × 6.375 = 2.391 in² φPn = 0.75 × 58 × 2.391 = 104.0 kips

Step 3 — Block shear (conservative assumption): Agv = 3/8 × 2 × 2.0 = 1.50 in² Anv = Agv − 1.5 × (3/4 + 1/16) × (3/8) = 1.50 − 0.457 = 1.043 in² Ant = 3/8 × 4.5 − 0.5 × (3/4 + 1/16) × (3/8) = 1.688 − 0.152 = 1.536 in² Ubs = 1.0

φRn = 0.75 × min(0.6 × 58 × 1.043 + 1.0 × 58 × 1.536, 0.6 × 36 × 1.50 + 1.0 × 58 × 1.536) = 0.75 × min(27.18 + 89.09, 32.40 + 89.09) = 0.75 × 116.27 = 87.2 kips

Governing capacity: 87.2 kips (block shear rupture controls).

Quick Reference Card

Parameter Value
Yield Fy 36 ksi / 250 MPa
Tensile Fu 58 ksi / 400 MPa
Modulus E 29,000 ksi / 200 GPa
Density 490 lb/ft³ / 7,850 kg/m³
φ for yielding 0.90 (AISC LRFD)
φ for rupture 0.75 (AISC LRFD)
CE typical 0.38–0.42
Preheat threshold t ≥ 3/4 in

References