C-Purlin and Z-Purlin are secondary structural members in light gauge steel framing systems, primarily used in roof and wall systems of industrial and commercial buildings. They support cladding materials such as color-coated steel sheets, sandwich panels, or PV modules, and transfer loads to primary frames (e.g., portal frames). The most common types are C-section and Z-section purlins, cold-formed from galvanized or aluzinc steel coils, offering light weight, high strength, easy installation, and excellent corrosion resistance.
Key Features
Main Types:
C-Purlin (C-Section)
"C"-shaped cross-section with symmetrical flanges.
Suitable for short spans and light loads.
Common sizes: C80, C100, C120, C140, C160, C200, C250 (number indicates height in mm).
Z-Purlin (Z-Section)
"Z"-shaped with a slight lip angle (e.g., 10°–16°), allowing continuous lapping over multiple spans.
Ideal for long-span, multi-bay roofs with superior structural performance.
Common sizes: Z80, Z100, Z120, Z140, Z160, Z200, Z250.
✅ Advantage of Z-Purlin: Enables continuous beam effect through lapping, reducing deflection and increasing load capacity.
Applicable Standards:
GB/T 50018-2002 – Technical code for cold-formed thin-wall steel structures (China).
GB/T 6725-2017 – General technical requirements for cold-formed sections.
GB/T 2518-2019 – Continuously hot-dip galvanized steel sheet/strip.
JIS G 3302 – Japanese standard for galvanized steel.
ASTM A653/A653M – Standard for zinc-coated steel (USA).
EN 10143:2006 – Tolerances on dimensions for cold-rolled sections (Europe).
AS/NZS 1365:1996 – Dimensional tolerances (Australia/New Zealand).
Materials (Base Steel Grades):
Q235B / S280GD: General strength for standard industrial buildings.
Q355B / S350GD / S550GD: High-strength steel for long-span or heavy-load roofs.
G300 / G550 (per ASTM A653): Yield strength ≥300 MPa or 550 MPa.
All grades must have good cold-forming ductility and weldability.
Zinc Coating Requirements:
Coating Types:
Hot-Dip Galvanized (GI): Coating mass 180–275 g/m² (double-sided).
55% Al-Zn (GL, Aluzinc): Superior corrosion resistance, e.g., AZ150 (150 g/m² Al-Zn alloy).
Standards: Compliant with GB/T 2518, ASTM A792, JIS G 3321.
Dimensional Range (Typical):
| Type | Height H (mm) | Web Thickness t (mm) | Flange Width b (mm) | Lip Width c (mm) |
| C-Purlin | 80 – 300 | 1.5 – 3.5 | 50 – 80 | 20 – 30 |
| Z-Purlin | 80 – 300 | 1.5 – 3.5 | 50 – 80 | 20 – 30 |
🔹 Weight Formula:
Weight (kg/m) = Cross-sectional Area (mm²) × 0.00785
Surface & Delivery Conditions:
Surface: As-galvanized (GI/GL), optional pre-painted or passivated.
Length: Cut-to-length or random, typically 6m – 12m.
Packaging: Bundled with moisture-proof paper and steel strapping, corner protectors.
Marking: Each bundle labeled with size, grade, length, batch number, manufacturer.
Main Applications:
Roofs and walls of factories, warehouses, logistics centers
Light roofs for commercial buildings, stadiums, exhibition halls
Solar racking systems (Z-purlins for sloped roofs)
Secondary structures in airports, train stations
Modular and prefabricated buildings
Key Advantages:
Lightweight reduces primary structural load.
Factory-precut, bolted on-site – fast installation.
Long service life (25+ years) with proper coating.
Recyclable and eco-friendly.
Cost-effective for mass industrial construction.
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