ASTM A709/A709M — Structural steel for bridges
Grades
Gr.36, Gr.50, Gr.50S, Gr.HPS 50W, Gr.HPS 70W, Gr.100, Gr.100W, Gr.HPS 100W
Chemical composition and mechanical properties
| Grade | Chemical composition | Mechanical properties |
|---|---|---|
| Gr.36 | C≤0.26, Mn 0.60-0.90, P≤0.040, S≤0.050, Cu≥0.20 (acceptable) | Rm 400-550 MPa, Rp0.2 ≥250 MPa, A≥23% |
| Gr.50 | C≤0.23, Mn≤1.35, P≤0.040, S≤0.050, Nb+V 0.01-0.15 | Rm ≥450 MPa, Rp0.2 ≥345 MPa, A≥21% |
| Gr.50S | C≤0.23, Mn 0.50-1.50, P≤0.035, S≤0.045, Si 0.15-0.40 | Rm ≥450 MPa, Rp0.2 ≥345 MPa, A≥21%, Yield strength ratio ≤0.85 |
Application scope
ASTM A709/A709M specifically specifies steel plates for bridge structures, covering carbon steel, high-strength low-alloy steel, and quenched and tempered alloy steel, including weather-resistant (W) and high-performance (HPS) varieties. The standard is divided into multiple grades according to yield strength, and specifies tensile, impact toughness, and weldability, taking into account strength, toughness, and weather resistance, and is applicable to welded or bolted bridge load-bearing components.
Typical applications
It is mainly used for the main beams, deck systems, bearings, and various load-bearing components of highway and railway bridges; the weather resistance rating can be used for exposed bridge structures that require no painting or minimal maintenance. With its classification by strength and toughness, and the inclusion of high-performance and weather-resistant varieties, it can be selected based on span, load, and environment, making it suitable for bridge projects with high requirements for safety, durability, and low-temperature toughness.
