Section Form and Why Angles Are Specified
An equal angle bar is a hot rolled section with two legs of the same width meeting at a right angle. The geometry provides bending stiffness in both principal axes, so the section is used where loading direction is not fully defined, and the flat outer faces make it easy to bolt, weld and drill. Because the legs are equal, the section is symmetric about the diagonal axis, which simplifies connection detailing compared with an unequal angle.
Angles are supplied in carbon steel grades rather than in high strength low alloy grades for most light and medium structural work, because the sections are thin walled and deflection or local buckling usually governs before yield strength does. Where additional strength is needed, the next higher grade is selected rather than a thicker leg, which keeps bolt gauge distances practical.
Steel Grades and Mechanical Properties
| Grade | Standard | ReH min (MPa) | Tensile strength (MPa) |
|---|---|---|---|
| A36 | ASTM A36/A36M | 250 | 400 - 550 |
| Q235B | GB/T 700-2006 | 235 up to 16 mm | 370 - 500 |
| Q345 | GB/T 1591-2008 | 345 up to 16 mm | 470 - 630 |
A36 is the default North American grade and also the standard material for bolted angle connections. Q235B is the general purpose Chinese structural grade for buildings, ladders, racks and supports. Q345, now generally superseded by Q355 in current Chinese practice, is used where the member carries higher load or where section depth is limited by the connection detail.
Chemical requirements follow the parent standard, and because angle sections are thin, the carbon and sulfur levels of these grades are low enough for routine welding without preheat under a qualified procedure. Certificate issue is normally to EN 10204 3.1 or to the acceptance class stated in the purchase order.
Size Range, Thickness and Length
Equal angles are produced with leg widths from 25 mm to 200 mm and thicknesses from 3 mm to 24 mm in common supply. Leg width, thickness and root radius determine the section area and radius of gyration used in the design check, and the mass per metre of a standard size is tabulated in the dimensional standard of the series.
| Size (mm x mm x mm) | Nominal mass (kg/m) | Dimensional standard family |
|---|---|---|
| 50 x 50 x 5 | 3.77 | GB/T 706-2016 / EN 10056-1 |
| 75 x 75 x 6 | 6.91 | GB/T 706-2016 / EN 10056-1 |
| 100 x 100 x 10 | 15.1 | GB/T 706-2016 / EN 10056-1 |
Standard delivery length is 6 m to 12 m, and cut to length supply is normal for fabrication orders. Dimensional tolerance is taken from GB/T 706-2016 for Chinese sections, EN 10056-1 for dimensions and EN 10056-2 for tolerances in the European system, JIS G3192 for Japanese sections and ASTM A6/A6M for American practice. Because these tolerance systems differ, each item must be inspected against its own standard.
Fabrication and Connection Practice
Angles are cut by saw or plasma, punched or drilled for bolts, and welded under procedures qualified to AWS D1.1/D1.1M, EN 1090-2 or ISO 15614-1. The most common defects in angle fabrication are edge distance violations at bolt holes and distortion caused by welding along one edge only, so hole positions are checked against the governing standard before assembly and welding sequence is planned to balance heat input.
Galvanizing to ASTM A123/A123M or EN ISO 1461 protects exposed angles in outdoor service. Angles are fabricated with drainage and venting holes before coating so that the zinc can enter and leave the section, and site cuts or welds are repaired with a zinc-rich coating.
Typical Applications
Equal angles are used for bracing and cross bracing, transmission tower legs and bracing, ladder stringers, cable trays, shelving and racking, machinery guards, base frames and connection cleats between beams and columns. In everyday steel work they are the standard choice for frames, benches and small structures because they are easy to cut, drill and weld with basic equipment.
Where the load is eccentric relative to the angle legs, the connection design accounts for the eccentricity rather than assuming the angle acts concentrically. This is the most frequent structural error in angle work and is normally resolved by using a gusset plate or by doubling the angle on both sides of the connection.
Frequently Asked Questions
Q: What is the difference between equal and unequal angle bar?
A: Equal angles have two legs of the same width and are symmetrical about the diagonal axis, which gives predictable behaviour in bracing. Unequal angles have different leg widths and are chosen where the connection geometry or the load direction calls for one long and one short leg.
Q: Which grade is equivalent to A36 in the Chinese system?
A: Q235B to GB/T 700-2006 is the closest match, with a minimum yield of 235 MPa against 250 MPa for A36, and a tensile range of 370 - 500 MPa against 400 - 550 MPa. Both are weldable carbon structural steels used for the same class of work.
Q: Can angle bar be supplied cut to length and drilled?
A: Yes. Angles are commonly cut to length, punched or drilled for bolt holes, and coped before galvanizing so that all cut faces receive coating. Producing holes before coating is preferred because drilling after coating damages the protective layer.
Q: How is the mass of an angle bar calculated for an order?
A: Order mass is based on the nominal mass per metre of the standard size multiplied by the supplied length, which is the practice used in the dimensional standard. Where a project requires weighing, the actual mass is usually compared against nominal with the tolerance stated in the standard.
Q: Are angle bars suitable for welded bracing in cold climates?
A: Yes, provided the grade has a certified impact requirement at the service temperature. Grades without a Charpy requirement, such as A36 and Q235B, are used in normal temperature service, while low temperature work needs a grade with a defined impact test temperature.
Q: What tolerance applies to the leg thickness of an angle?
A: Leg thickness and leg width tolerance are governed by the dimensional standard of the series, with the permitted deviation stated as a band or percentage of nominal thickness. For European supply, EN 10056-2 is the document that applies.