ASTM A709 — Yield Strength, Tensile Strength and Applications
The bridge umbrella spec. A709-26 lists twelve grades that parallel A36, A992, A588, A913 and stainless A1010, with bridge-specific toughness and quality requirements. Use where American Association of State Highway and Transportation Officials (AASHTO) or a Department of Transportation (DOT) invokes it.
Strength
| Grade | Fy (ksi) | Fu (ksi) | Note |
|---|---|---|---|
| 36 | 36 | 58 | Parallels A36. |
| 50 | 50 | 65 | Non-weathering. |
| 50S | 50–65 | 65 | Shapes. Fy/Fu ≤ 0.85 (0.87 web-tested). Parallels A992. |
| 50W | 50 | 70 | Weathering; parallels A588 (46/42 ksi over 4 in.). |
| 50CR | 50 | 70 | Stainless (formerly A1010) plate; corrosion-resistant without paint. |
| QST 50 | 50 | 65 | Quenched and Self-Tempered (QST) shapes; parallels A913 Grade 50. |
| QST 50S | 50–65 | 65 | QST shapes with capped Fy and ratio. |
| QST 65 | 65 | 80 | QST shapes; parallels A913 Grade 65. |
| QST 70 | 70 | 90 | QST shapes; parallels A913 Grade 70. |
| HPS 50W | 50 | 70 | Plate only. Improved toughness and weldability. |
| HPS 70W | 70 | 85–110 | Plate only. Fu is a range; design uses 85 ksi. |
| HPS 100W | 100 | 110–130 | Plate ≤ 2.5 in. Over 2.5 to 4 in.: Fy 90 ksi. Design uses Fu = 110 ksi. |
Fy and Fu are specification minimums. Verify the grade on the Mill Test Report (MTR); dual-certified material is common.
Applicable members
Plates and shapes (grade-dependent); shape grades cover W, S, M, HP, C, MC, L, WT, MT, ST
Applicable is not the same as stocked. Confirm availability with the supplier.
Common applications
Highway and rail bridges, fracture-critical members, DOT-governed structures.
Field notes
- The value is the toughness and quality requirements, not the base strength.
- Charpy V-Notch (CVN) and testing requirements depend on grade, member category and project provisions. They are invoked on the order by the T (non-fracture-critical) or F (fracture-critical) suffix and temperature zone 1–3, e.g. A709 Grade 50W T2.
- Never swap in a building-grade equivalent on a bridge without carrying the toughness requirements.
- High-Performance Steel (HPS) grades are plate only; they cut weight and improve field weldability on long-span girders. QST grades are shapes only.
Material constants
- Modulus of elasticity E: 29,000 ksi
- Shear modulus G: 11,200 ksi
- Density: 490 lb/ft³ (0.284 lb/in³)
- Poisson's ratio: 0.30
- Thermal expansion: 6.5 × 10⁻⁶ in/in/°F
These are the same for every structural steel grade. Strength changes with the specification; stiffness does not.
Related
- ASTM Structural Steel Grades Reference
chemistry, tolerances and the full specification behind this grade
- Steel Shape Properties Table
the sections this grade is supplied in
- Bolt Tensile & Shear Capacity Calculator
fastener grades to match this base metal
- Fillet Weld Strength Calculator
electrode selection to match this base metal
The full specification
Chemistry, tolerances, coatings, galvanizing, weldability, availability and substitutions for every spec: ASTM 101 (STL+).