What the 100 x 100 x 5 mm Equal Angle Section Gives You
A 100 x 100 x 5 mm hot rolled equal angle has two legs of 100 mm at a thickness of 5 mm, forming a rigid L shaped section that resists bending in both directions and carries compression loads without a separate web or flange. Its section area is about 9.75 cm2 and its nominal mass is about 7.65 kg/m, so a 6 m length weighs roughly 46 kg and can be handled with light lifting equipment or a two-person team. Because the two legs are equal, the section is symmetric about the 45 degree axis, which makes it easy to detail in back-to-back pairs, star struts and braced frames.
The section is produced by hot rolling, so the surface carries mill scale, the corners are rounded and the material retains the ductility of a structural carbon steel rather than the work-hardened condition of a cold formed profile. That combination is what makes the size suitable for both welded frames and bolted connections.
Grade Comparison: A36, SS400, Q235B and Q345B
| Grade | Standard | Yield, min (MPa) | Tensile (MPa) | Elongation, min (%) | Impact requirement |
|---|---|---|---|---|---|
| A36 | ASTM A36 | 250 | 400-550 | 20 | not specified |
| SS400 | JIS G3101 | 245 | 400-510 | 17 | not specified |
| Q235B | GB/T 700 | 235 | 370-500 | 26 | 20 C, 27 J |
| Q345B | GB/T 1591 | 345 | 470-630 | 21 | 20 C, 34 J |
The chemical requirements differ in character as well as in number. A36 fixes a heat analysis with carbon at 0.25% maximum, manganese of 0.80-1.20%, silicon at 0.40% maximum, phosphorus at 0.04% maximum and sulphur at 0.05% maximum. Q235B to GB/T 700 caps carbon at 0.20%, manganese at 1.40%, silicon at 0.35% and both phosphorus and sulphur at 0.045%, which is what separates the B quality class from the basic A class. JIS G3101 defines SS400 mainly through mechanical properties rather than a single fixed analysis, so producers control carbon and manganese to land inside the 400-510 MPa tensile window. Q345B, the old designation for what GB/T 1591 now calls Q355, allows manganese up to about 1.60% and silicon up to about 0.55%, and the B quality class is defined by a Charpy V-notch impact test at 20 C with a minimum absorbed energy of 34 J.
In use, the four grades are interchangeable for most static framing, but not for cold-climate or dynamic work: Q345B is the choice where higher strength or a guaranteed impact value is required, while A36, SS400 and Q235B are selected on price, availability and the standard quoted on the drawing.
Mass, Section Area and Detailing Data
| Equal angle size | Section area (cm2) | Theoretical mass (kg/m) | Mass of a 6 m length (kg) |
|---|---|---|---|
| 75 x 75 x 6 mm | 8.64 | 6.78 | 40.7 |
| 100 x 100 x 5 mm | 9.75 | 7.65 | 45.9 |
| 100 x 100 x 10 mm | 19.00 | 14.92 | 89.5 |
| 125 x 125 x 8 mm | 19.36 | 15.20 | 91.2 |
| 150 x 150 x 12 mm | 34.56 | 27.13 | 162.8 |
The masses above are theoretical values calculated from the sharp-corner section area at a steel density of 7.85 g/cm3, which is the same convention used in rolled section tables; actual mass differs only slightly because of roll tolerances. All four grades have essentially the same density, so choosing Q345B instead of Q235B does not change the weight of a delivered bundle; it only changes the strength available from that weight.
For detailing, the 5 mm leg limits direct bolting to fasteners up to about M16 and calls for washers under both head and nut to spread the bearing pressure, while welded connections should keep the fillet leg within the thickness of the thinner part. Where the section is used in compression over a long span, the slenderness ratio usually governs well before the yield strength of the steel is reached, which is why a higher grade does not always allow a smaller angle to be substituted.
Welding, Coatings and Durability
A36, SS400 and Q235B weld with E70XX electrodes or ER70S-6 filler and normally need no preheat at 5 mm thickness.
Q345B is welded with matching higher-strength or low-hydrogen consumables, and heat input is controlled to preserve the toughness of the heat-affected zone.
Mill scale and rust are removed along the joint because they cause porosity and lack of fusion in fillet welds.
Hot-dip galvanising to ISO 1461 gives steel between 3 mm and 6 mm thick a minimum average coating of 70 micrometres, which suits outdoor and mildly corrosive service.
Where galvanising is impractical, a zinc-rich primer followed by a suitable topcoat gives comparable protection, and uncoated steel is kept dry and ventilated to avoid rusting.
None of the four grades is a weathering steel, so service in humid, coastal or chemically loaded environments depends on the coating system rather than on the base metal. Fixings and adjacent materials should be chosen to avoid a galvanic couple with the zinc coating, and cut edges and drilled holes are best protected with a zinc-rich repair coating after fabrication.
Typical Construction Applications
Primary and secondary framing for industrial sheds, warehouses and mezzanine floors.
Bracing, tie members, gusset stiffeners and column base details.
Walkway, platform and stair framing, guard rail posts and handrail supports.
Pipe racks, cable tray supports, conveyor and equipment mounting frames.
Racking uprights and beams, pallet support structures and shelving frames.
Bridge railings, sign gantries, temporary works and formwork supports.
The size is popular because it balances a stiff cross-section against a mass that stays within the lifting capacity of small site equipment, and because standard connection hardware for M12 to M16 bolts fits the 100 mm legs without special fabrication. Bundles are identified by heat number and supplied with mill test certificates covering chemistry, tensile properties and, for the Q grades, the impact test result.
Frequently Asked Questions
Q: How much does 100 x 100 x 5 mm angle steel weigh per metre?
The section area is about 9.75 cm2, giving a theoretical mass of about 7.65 kg/m at a density of 7.85 g/cm3, so a 6 m length weighs roughly 46 kg and a 12 m length about 92 kg.
Q: Is A36 the same as SS400?
Both are general structural steels of similar strength, but A36 is an ASTM grade with a specified analysis and a 250 MPa minimum yield, while SS400 is a JIS grade defined mainly by properties with a 245 MPa minimum yield and a 400-510 MPa tensile range.
Q: Which grade suits cold or dynamic loading?
Q345B is impact tested at 20 C with a minimum absorbed energy of 34 J and has a higher yield strength, so it performs better than Q235B under low-temperature or fatigue loading; colder service than 20 C calls for a C, D or E quality class.
Q: Can the four grades be welded to each other?
Yes. The filler is matched to the higher-strength grade, low-hydrogen consumables are used for Q345B and for thicker sections, mill scale is cleaned from the joint faces, and welding procedure qualification is based on the combination actually used.
Q: How is a 100 x 100 x 5 mm angle protected outdoors?
Hot-dip galvanising to ISO 1461 provides a minimum average coating of 70 micrometres at this thickness, and where galvanising is not practical a zinc-rich primer with a topcoat is used, with cut edges and holes repaired after fabrication.
Q: What tolerances apply to leg length, thickness and straightness?
Dimensional tolerances follow ASTM A6 for A36, JIS G3192 for SS400 and GB/T 706 for the Q grades, covering leg length, thickness, squareness and straightness; the permissible deviations are small relative to the member size and do not affect bolted or welded connections.