Grade Range for Bridge Work
Bridge structures call for steel with a certified strength and a defined toughness. The angle bars used for bracing, stiffeners and connection details are commonly supplied in ASTM A36 with a minimum yield strength of 250 MPa, in S235JR and S275JR under EN 10025-2 with minimum yield strengths of 235 MPa and 275 MPa, in ASTM A572 Grade 50 with a minimum yield strength of 345 MPa, and in SS400 under JIS G 3101 with a minimum yield of 245 MPa. The higher strength grades reduce the weight of bracing and cross frames, while the lower strength grades remain economic for secondary members. In all cases the toughness requirement should be matched to the lowest service temperature of the site.
Mechanical Properties and Toughness
EN 10025-2 grades carry a Charpy requirement: S235JR and S275JR are tested at 20 degrees Celsius with a minimum energy of 27 J. For lower temperatures the designer should specify S235J0 or S275J0 at zero degrees Celsius, or S235J2 and S275J2 at minus 20 degrees Celsius. ASTM A36 does not guarantee impact energy unless it is ordered as A36 with a supplementary impact requirement.
| Grade | Minimum Yield MPa | Tensile Range MPa | Impact Test Temperature |
| A36 | 250 | 400 to 550 | Not guaranteed unless specified |
| S235JR | 235 | 360 to 510 | 20 degrees Celsius |
| S275JR | 275 | 410 to 560 | 20 degrees Celsius |
| A572 Grade 50 | 345 | 450 minimum | Not guaranteed unless specified |
| SS400 | 245 | 400 to 510 | Not guaranteed unless specified |
Equal and Unequal Angel Sections in Bridge Detailing
Equal angles are used for cross bracing and lateral support between girders, while unequal angles with a long leg and a short leg are used for connection cleats and edge stiffeners where the bolt group needs an offset. Both are covered by GB/T 706 for metric dimensions, by EN 10056 for European dimensions and by ASTM A6 for inch sizes. Bolted connections dominate bridge bracing because they can be assembled and inspected on site. Slip critical joints should be designed with the specified surface preparation, and the angle must be supplied with the hole pattern and edge distances agreed before fabrication.
Fabrication and Protection
Bridge fabrication requires traceable material, documented welding procedures and dimensional control. Angles are cut to length, drilled rather than punched where fatigue matters, and welded only with a qualified procedure when the design uses welded connections. Corrosion protection is the decisive factor for service life. Hot dip galvanizing is common for smaller bracing members, while heavy duty painting systems or metal spraying are used for large structures. Drainage and detailing should avoid water traps between the angle and the main girder.
Typical Bridge Applications
Lateral and cross bracing between plate girders.
Stiffener and diaphragm connection cleats.
Edge trim and walkway supports.
Temporary works and erection bracing.
Bearing seat and anchorage details.
Frequently Asked Questions
Q: Which angle grade is best for cold region bridges?
S235J0, S275J0, S235J2 and S275J2 are preferred because they carry impact requirements at zero degrees Celsius or minus 20 degrees Celsius, while A36 needs a supplementary impact order.
Q: Why are unequal angles used in bridges?
Unequal angles give a wider or longer leg on one side, which suits connections where the bolt group must clear the main member or where a stiffener must follow a curved edge.
Q: Are angle bars bolted or welded in bridge work?
Both are used, but bolted connections dominate bracing because they are easier to assemble and inspect on site and avoid heat input to the main girder.
Q: How is the angle protected against corrosion?
Hot dip galvanizing, heavy duty paint systems and metal spraying are the usual methods, selected according to the corrosivity category and the required maintenance interval.
Q: What documentation is needed for bridge steel?
Material certificates with traceable heat numbers, welding procedure qualification records, dimensional inspection reports and coating thickness records are normally required.