GB Standard Framework, Grades and Sections
GB standard angle steel is produced to GB/T 706, which governs the dimensions, mass and permissible tolerances of hot rolled section steel including equal leg and unequal leg angles. The steel itself is normally ordered to GB/T 700 for Q235B or to GB/T 1591 for Q355B, so the purchaser specifies a section standard and a grade standard together. Typical leg sizes run from L40x40x4 up to L200x200x24, with wall thicknesses matched to the design load and to the bolt or weld capacity of the connection.
| Item | Typical specification |
|---|---|
| Section standard | GB/T 706 |
| Carbon steel grade | Q235B to GB/T 700 |
| Low alloy grade | Q355B to GB/T 1591 |
| Yield strength, Q235B | 235 MPa minimum |
| Yield strength, Q355B | 355 MPa minimum |
| Hot dip galvanizing | GB/T 13912 |
Section size is chosen together with the grade. A Q235B angle is economical for light bracing and secondary framing, while Q355B allows a smaller or thinner section to carry the same load, which reduces steel weight in towers, cranes and long span supports. Tolerances on leg length, thickness and straightness matter as much as strength in bolted assemblies, because a twisted angle forces fit up stress into the joint.
Construction Sector Applications
In building work, GB angles are found in roof trusses, staircase and balustrade framing, partition supports, lintel and opening reinforcement, plant platforms and facade fixing steel. In apartment framing, small sections such as L40x40x4 are used for secondary framing and supports, while larger sections such as L125x125x10 carry column bracing in factory buildings. Galvanized or painted angles are specified for exposed balconies, canopies and external stairs, where coating durability determines service life.
Roof trusses, purlins and ridge bracing
Staircase railings, stringers and platform edge protection
Partition and cladding support frames
Column bracing and crane runway supports in industrial halls
Equipment foundations and machine base frames
Infrastructure Projects
Infrastructure uses GB angles where repetitive, easily erected members are needed. Highway and railway works consume them for bridge substructure supports, guardrails and parapet frames, with sections such as L75x75x8 used in overpass works. Power transmission projects use angles as tower components, cross arm bracing and cable supports, frequently in galvanized condition, with sections such as L63x63x6 used in transmission line towers. Drainage and utility works use angles for support brackets, trench covers and pipe anchoring.
Manufacturing and Machinery
Manufacturing industries consume GB angles in frames, guards, trolleys and machine bases. Conveyor systems, agricultural machinery and vehicle trailers are typical end products, with sections such as L56x56x5 used in truck and trailer frame fabrication. The grade selection in these applications usually follows the fabrication method: Q235B where formability and weldability dominate, Q355B where a lighter frame must carry a heavier dynamic load. Punching, shearing and bending limits should be respected, and deformation from welding should be controlled to keep frames square.
Renewable Energy and Other Projects
Renewable energy projects have become a significant outlet for GB angles. Solar mounting structures typically use galvanized L60x60x5 or similar sections for rail supports, array frames and foundation brackets, where corrosion resistance is the deciding factor because the steel stays exposed for decades. Wind and biomass plants use angles for internal platforms, cable ladder supports and auxiliary frames. Cold formed and hot rolled angles both appear, and the choice depends on required thickness accuracy, hole position tolerances and the finish that the site can be maintained with.
Frequently Asked Questions
Q: Which standard governs GB standard angle steel?
GB/T 706 governs the dimensions, mass and tolerances of hot rolled angles, while GB/T 700 and GB/T 1591 govern the Q235B and Q355B grades.
Q: Which industries use GB angle steel most heavily?
Building construction, infrastructure such as bridges and transmission towers, manufacturing frames and trailers, and renewable energy mounting structures.
Q: Is Q355B better than Q235B for angle steel?
Q355B offers a yield strength of at least 355 MPa against 235 MPa for Q235B, so it suits heavier loads or lighter sections, but it costs more and is not needed everywhere.
Q: How is GB angle steel protected from corrosion?
Hot dip galvanizing to GB/T 13912 is the usual choice for exposed and outdoor work, with painting or a combined system used where appearance or chemical exposure requires it.
Q: What sizes of GB angle steel are common?
Equal leg angles from L40x40x4 up to L200x200x24 cover most building, tower, machinery and solar mounting requirements.
Q: Can GB angle steel be drilled and welded on site?
Yes. Both Q235B and Q355B angles are routinely punched, drilled, bolted and welded, provided that welding follows an approved procedure for the grade and thickness.