What Steel Grades Are Commonly Used for Bridges?
Bridge projects commonly use dedicated bridge structural steels such as Q345q, Q370q, and Q420q in China, while ASTM A709 grades are widely specified in the US, and S355 grades may appear in projects following European standards.
But bridge steel is not just about yield strength. When purchasing, you also need to consider impact toughness, plate thickness, weldability, design temperature, corrosion resistance, Z-direction properties, UT requirements, and the applicable bridge design standard.
This guide covers the most common bridge steel grades across Chinese, American, and European standards — and what buyers should check before ordering.
1. What Is Bridge Steel?
Bridge steel is a dedicated category of structural steel designed for bridge construction. It differs from general structural steel in several ways:
- ✔ Higher strength — to handle vehicle loads, dead loads, dynamic loads, wind loads, and temperature changes
- ✔ Better impact toughness — bridges are exposed to outdoor environments, and low-temperature toughness is critical
- ✔ Good weldability — bridges use extensive welded structures
- ✔ Stricter quality control — chemical composition, mechanical properties, impact testing, thickness tolerance, UT, and MTC requirements
2. Common Chinese Bridge Steel Grades
The Chinese bridge steel standard is GB/T 714. The most common grades are:
📌 Note: The Chinese bridge steel grade system has evolved from Q345q/Q370q to include Q420q, Q500q, and even Q690q for major projects [citation:1]. GB/T 714-2025 also added Q390q, Q550q, Q620q, and Q690q grades [citation:2].
2.1 Q345qC, Q345qD and Q345qE
Q345q ≠ Q345B. The "q" stands for "桥" (bridge), indicating this is a dedicated bridge steel.
- ✔ Q345 = strength level
- ✔ q = bridge structural steel
- ✔ C/D/E = different impact toughness temperature requirements
The letters indicate impact test temperatures: C = 0°C, D = -20°C, E = -40°C [citation:5][citation:6]. The exact requirements should always be confirmed against the applicable GB/T standard and project specification.
2.2 Q370qC, Q370qD and Q370qE
Q370q offers higher strength than Q345q. It is useful when designers need higher load-bearing capacity and potentially allows structural weight optimization. However, welding and toughness still require attention.
2.3 Q420qC, Q420qD and Q420qE
Q420q is a higher-strength bridge steel used for demanding structural applications. But it is not automatically the best choice simply because its strength is higher.
⚠️ Important: A higher steel grade does not always mean a better choice. The grade must match the structural design.
3. Q345qC vs Q345qD vs Q345qE: What Is the Difference?
The difference is not simply the strength level — it is the impact toughness requirement.
- ✔ Yield strength: basically the same grade level (345 MPa)
- ✔ Tensile strength: grade-dependent
- ✔ Impact toughness: different temperature requirements (0°C, -20°C, -40°C)
💡 Key point: Project temperature is an important factor when selecting C/D/E. The exact acceptance temperature and requirements must be confirmed against the applicable standard and order specification.
4. Q345q vs Q345B: Are They the Same?
Conclusion: Q345q should not be treated as a simple substitute for Q345B just because their strength levels appear similar.
5. ASTM A709 Bridge Steel Grades
For projects following US standards, ASTM A709 is the primary specification for bridge structural steel [citation:3][citation:10].
- ✔ A709 Grade 36 — 250 MPa yield strength
- ✔ A709 Grade 50 — 345 MPa yield strength, most common bridge grade
- ✔ A709 Grade 50W — weathering bridge steel with enhanced atmospheric corrosion resistance
6. European Bridge Steel Grades
- ✔ S355J2 — commonly used for bridge plates up to 50mm thick [citation:4]
- ✔ S355K2 — used for thicker plates (55-70mm) requiring higher toughness [citation:4]
- ✔ Weathering grades: S355J0W, S355J2W [citation:11]
⚠️ Important: European structural steel grades and Chinese bridge steel grades should not be considered automatically equivalent. Do not assume Q345q = S355J2 without checking the full specification.
7. How to Choose the Right Bridge Steel Grade?
Step 1: Check the design standard — GB/T, ASTM, EN, or project-specific
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Step 2: Check required strength — yield, tensile, thickness
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Step 3: Check impact toughness — design temperature, Charpy V-notch requirements
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Step 4: Check welding requirements — carbon equivalent, procedure, preheating
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Step 5: Check Z-direction requirements — Z15 / Z25 / Z35
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Step 6: Check UT requirements — standard, testing level, acceptance criteria
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Step 7: Check inspection and certification — MTC, third-party inspection, traceability
8. Bridge Steel Plate Thickness and Delivery Requirements
Bridge steel procurement cannot be based on grade alone. You need to confirm:
- ✔ Thickness, width, length, quantity
- ✔ Delivery condition
- ✔ Impact testing requirements
- ✔ UT requirements
- ✔ Surface requirements
- ✔ MTC and inspection requirements
📌 Example: Q345qC 20 × 2500 × 12000 mm and Q345qC 60 × 2500 × 12000 mm have the same grade but different production, rolling, delivery, and testing requirements.
9. Common Mistakes When Buying Bridge Steel
❌ Mistake 1: Treating Q345q as Q345B
They are different steel categories with different requirements.
❌ Mistake 2: Choosing the grade only by yield strength
Impact toughness, weldability, and inspection requirements matter equally.
❌ Mistake 3: Ignoring impact test temperature
A plate tested at 0°C is not suitable for -40°C service.
❌ Mistake 4: Assuming different standards are automatically equivalent
Q345q is not the same as S355J2 or A709 Grade 50.
❌ Mistake 5: Confirming the grade but not the inspection requirements
UT, impact testing, and MTC requirements should be confirmed before ordering.
❌ Mistake 6: Waiting until production to discuss UT or third-party inspection
Inspection requirements must be agreed before production, not after.
10. Q345q, Q370q or Q420q: Which One Should You Choose?
- ✔ Q345q — common choice for many bridge structures
- ✔ Q370q — when higher strength is required
- ✔ Q420q — when the project calls for higher-strength bridge steel
💡 Key point: The final selection should come from the structural design and project specification — not from the steel supplier alone.
11. Frequently Asked Questions
❓ What is the most commonly used bridge steel grade?
In China, Q345qD is one of the most widely used bridge steel grades. In the US, ASTM A709 Grade 50 is common. The choice depends on the project's design standard and location.
❓ What is Q345qC steel?
Q345qC is a Chinese bridge steel grade with a minimum yield strength of 345 MPa. The "C" indicates impact testing at 0°C. It is used for bridge structural members in moderate climates.
❓ What is the difference between Q345qC and Q345qD?
The main difference is the impact test temperature. Q345qC is tested at 0°C, while Q345qD is tested at -20°C. Q345qD offers better low-temperature toughness.
❓ Is Q345q the same as Q345B?
No. Q345q is a dedicated bridge steel under GB/T 714, while Q345B is a general structural steel under GB/T 1591. They have different toughness requirements and inspection standards.
❓ What is Q370q steel used for?
Q370q is a higher-strength bridge steel used for bridge structures requiring greater load-bearing capacity. It allows designers to optimize structural weight.
❓ What is ASTM A709 Grade 50?
ASTM A709 Grade 50 is a high-strength low-alloy steel for bridge construction with a minimum yield strength of 345 MPa. It is one of the most common bridge steel grades in the US.
❓ Is S355J2 equivalent to Q345q?
They are similar in strength level but belong to different standard systems. They should not be considered automatically equivalent without checking chemical composition, mechanical properties, and project requirements.
12. Final Thoughts
When sourcing bridge steel, the grade is only the starting point. The applicable standard, thickness, impact toughness, welding requirements, and inspection conditions should all be confirmed before production.
For buyers: confirm the design standard, required strength, impact temperature, Z-direction properties, UT requirements, and MTC requirements. A grade alone is not a complete purchasing specification.
💡 Our view: We supply and export Q345qC, Q345qD, Q345qE, Q370q, and Q420q bridge steel plates. Send us your design standard, grade, thickness, and inspection requirements — we'll source the right material and provide full MTC documentation.
📚 Further Reading & Related Content
- 🔗 Corten Steel vs Weathering Steel: What Is the Difference?
- 🔗 How to Read a Steel Plate Mill Test Certificate (MTC)
- 🔗 Why Choosing the Right Steel Plate Matters More Than the Lowest Price
- 📄 GB/T 714-2025, ASTM A709/A709M, EN 10025
Need Bridge Steel Plates?
CEHE STEEL supplies bridge steel plates including Q345qC, Q345qD, Q345qE, Q370q, and Q420q. Send us your grade, thickness, and standard — we'll provide a quotation with full MTC documentation.