Container Sections | Cold-Formed Steel for Container Frames
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RBT is a manufacturer of cold-formed sections used in the construction of durable and high-strength steel structures. Cold-formed sections are the foundation for the production of modern container frames and modular construction, among others. Unlike hot-rolled structural steel, container sections are manufactured using LGS (Light Gauge Steel) technology. This method offers precisely engineered cross-sections with mechanical parameters tailored to actual loads – eliminating material excess. Cold-forming technology allows for the processing of sheet metal in thicknesses ranging from 0,50 mm to 4,0 mm. Typical cross-sectional shapes include C, U, Z, and Omega (Ω), along with mounting holes, punched directly on a CNC-controlled production line.
A manufacturer of cold-formed sections for modular construction provides several key advantages:
- lower overall container frame weight
- factory-applied anti-corrosion coating
- full compliance with the EN 1090 standard
- CE marking
Technical Comparison: Cold-Formed vs. Hot-Rolled Sections
Container sections for the manufacturing of container frames can be produced using two methods:
- cold-forming
- hot-rolling
For an engineer designing a container frame (e.g.: 20 ft or 40 ft), the choice of technology directly impacts the total frame weight, corrosion protection costs, and assembly time.
The following table presents the structural parameters for both technologies:
| Feature | Cold-Formed Sections (LGS) | Hot-Rolled Structural Sections |
| Structural Weight | 20–40% weight reduction while maintaining load-bearing capacity through I_x / W_x optimization | High dead weight, increasing transport and foundation costs |
| Element Length | Fully customizable to project requirements (up to 12.5 m) | Limited to standard mill commercial lengths |
| Cross-section Geometry | High design flexibility: C, U, Z, Ω, and multi-bend custom channels | Limited, standardized dimensions – no possibility for geometric customization |
| Corrosion Protection | Ease of full surface protection (open profiles); factory-applied Z275 or Zinc-Magnesium coating | Difficulty in protecting the internal surfaces of closed mill sections |
| CNC Prefabrication | Punching, notches, and bevels with ±0.1 mm tolerance directly from the production line | Requires labor-intensive mechanical processing after purchase (drilling, milling, cutting) |
| Certification | Full compliance with EN 1090-2, classes EXC2/EXC3/EXC4; CE marking | Dependent on mill certification; requires additional executive documentation |
| Steel Grades | S390GD (Rp0,2 ≥ 390 MPa), S350GD (Rp0,2 ≥ 350 MPa), S355JR (Rp0,2 ≥ 355 MPa), S235JR (Rp0,2 ≥ 235 MPa) | S235, S355, S275 – standard commercial grades, not optimized for continuous coatings |
The key advantage of cold-formed container sections is the strength-to-weight ratio. At the same flexural rigidity, a cold-formed section achieves up to a 40% lower linear mass than its hot-rolled counterpart. This results from cross-sectional shape optimization: achieved through additional edge stiffeners (bends). For the Omega section, the moment of inertia (Ix) increases without increasing the wall thickness (Young’s modulus E=210GPa for steel; deflection δ < L/500 for S350GD steel at t=2,0 mm).
Corner Posts
Bottom Rails
Top Rails
Cold-Formed Sections for Container Construction – Technical Specification
Steel Grades: S350GD, S390GD, and DX51D Galvanized Steel
Container sections are manufactured from steel grades selected for their yield strength, weldability, and compatibility with continuous hot-dip galvanizing lines. The thickness range from 0,50 mm to 4,0 mm covers both lightweight cladding components and heavy-duty structural beams for the entire container frame.
| Grade | Rp0,2 (MPa) | Rm (MPa) | Container Application |
|---|---|---|---|
| S350GD | ≥ 350 | 420–550 | Offshore / marine frames, corner posts, perimeter beams |
| S390GD | ≥ 390 | 460–600 | Roof purlins, longitudinal rails, load-bearing frame components |
| S235 | ≥ 235 | 360–510 | Facade substructure / cladding support |
| DX51D | ≥ 140 | 270–500 | Galvanized sheet for cladding and flashings |
For office containers and modular construction, S235 or S355 steel grades with a Z275 coating are sufficient. However, for offshore/shipping containers operated in C5-M environments, S350GD steel with a zinc-magnesium coating (e.g.: ZM310 3% Mg + 3.5% Al) is recommended. The zinc-magnesium coating possesses a unique self-healing capability: in cut zones or scratched areas, the Mg–Al layer actively provides galvanic protection to the edge, limiting edge corrosion to < 1 µm/year (compared to 8–10 µm/year for Z275 coating in marine conditions, according to ISO 9227).
Sheet Thickness: from 0,50 mm to 4,0 mm
Container section production is carried out using continuous roll-forming lines and CNC press brakes. Key process parameters include:
- Wall Thickness: 0,50–4,0 mm (thickness tolerance per PN-EN 10143 and PN-EN 10051)
- Section Width: Tolerance ±1 mm per 1000 mm of length
- Straightness: 1 mm/m
- Element Length: Up to 12,5 m
- CNC Punching: Circular, oval, and custom holes
- All components are manufactured under a Factory Production Control (FPC) system in compliance with EN 1090, which constitutes the formal requirement for CE marking on sections intended for steel structures.
Structural Durability: Compliance with EN 10162 and CE Certification
The production of container sections and steel profiles for modular construction requires certification of compliance according to EN 1090-1 (requirements for structural components) and EN 1090-2 (technical requirements for steel structures). Execution classes EXC2, EXC3, and EXC4 differ in their requirements regarding welding, Non-Destructive Testing (NDT), and personnel qualifications.
A Z275 zinc coating provides 20–30 years of protection in moderate environments (corrosivity classes C2-C3 per ISO 9223). In contrast, a zinc-magnesium coating, such as ZM310, exceeds 2000 hours in salt spray testing (ISO 9227) and is certified for class C5-M (marine/heavy industrial environments) – offering a fivefold improvement in edge durability compared to Z275 without the need for additional painting.
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Key Container Profiles – Structural Frame Components
The container frame is constructed from several types of load-bearing components, each consisting of a distinct cold-formed section with optimized geometry. Below, we discuss each element in terms of its engineering requirements.
Top Rail – Multi-functional Load-bearing and Drainage Section (Perimeter Gutter)
Top Rail – The perimeter gutter is one of the most geometrically demanding components of the container frame. It serves a dual role: as a perimeter gutter for rainwater drainage and as a structural top rail that transfers loads from the roof cladding, purlins, and corner posts.
The section is manufactured as a cold-formed channel with multiple edge bends (approx. 6–8 bends). Typical parameters include: flange width b=60–120 mm, web height h=150–200 mm, and wall thickness t=1,5–3,0 mm, using S350GD + Z275 or S350GD + ZM310 steel. The profile’s geometry inherently provides the perimeter gutter function, eliminating the need for an additional drainage system.
Top Perimeter Rail
Top Rail / Gutter Section
Top Rail L-Section
Corner Post with ISO Lifting Holes / Transport Aperture
The corner post is a critical load-bearing component of the container frame, connecting the bottom perimeter beam to the top rail (gutter) and transferring vertical loads from each corner module. Standardized ISO corner castings with specialized transport apertures can be optionally installed at the frame corners.
Post Sections:
- closed section (hollow profile)
- open C-channel section
- C-channel with returned flanges – designed to simplify assembly and allow for utility installations (cabling/piping) to be routed through the interior of the profile
Parameters: h=150–300 mm, sheet thickness t=3,0–4,0 mm, steel grade S350GD or S355JR. The returned flanges increase the local moment of inertia of the flange by approximately 18% without increasing the material thickness.
Corner Post L-Section
5-bend C-section Corner Post
4-bend C-section Corner Post
Bottom Perimeter Beam and Structural Crossmembers (C-section & Omega-section)
Bottom perimeter beam transfers loads from the floor and constitutes the main structural member of the entire container frame in the horizontal plane. It is manufactured as a cold-formed C-section (h=160–250 mm, b=60–80 mm, t=3,0–4,0 mm), made of S350GD or S390GD steel.
C-section and Omega-section floor crossmembers link the bottom perimeter beam at a spacing of approximately 300–600 mm. The Omega (Ω) section is particularly advantageous in floor reinforcement systems: its shape distributes loads evenly in both transverse directions. Sheet thickness t=2,0–3,0 mm, made of S235JR, S355JR or S350GD, S390GD steel.
Bottom perimeter rail – 5-bend C-section
Bottom perimeter rail – 3-bend C-section
Bottom perimeter rail – 1-bend L-section
Floor crossmember-4-bend Omega-section
Floor crossmember-2-bend C-section
Floor crossmember-4-bend C-section
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Roof cladding: Standing seam flat sheet and trapezoidal sheet
The container roof system is implemented as a standing seam flat sheet or a trapezoidal sheet (e.g.: T18/T35). The flat sheet, made of DX51D + Z275 steel with a thickness of 0,60–0,75 mm, is formed with a standing seam of approx. 25 mm. This eliminates thermal bridges and capillary-stress gaps. Roof purlins (stringers) consist of C or Z-sections h=100–200 mm, t=2,0 mm spaced up to 1200 mm apart. Roof pitch: min. 2% for effective water drainage via the upper perimeter gutter.
Standing seam cladding
Trapezoidal sheet cladding
Trapezoidal sheet cladding
Modern cladding systems and flashings for containers
Corner cassettes and flat facade panels made of galvanized steel sheet
Container facade cassettes and panels are manufactured from 0,70–1,00 mm thick DX51D + Z275 steel sheet. The facade cassette (corner cassette) is formed with a cross-sectional depth of 40–80 mm, ensuring resistance to buckling under wind pressure ≥1,5 kN/m². The internal space of the cassette serves as a ventilated facade gap (min. 20 mm), eliminating water vapor condensation.
The cassette and panel sets are delivered with pre-drilled holes and CNC-formed corners – allowing for easy bolt-on assembly without the need for on-site welding. Flashings (windowsills, framings, linear drainage) are manufactured using the same edge-bending technology.
Corner Trim
Window Sill
Facade Panel
Facade sub-frame: Omega Ω, C, and Z-sections
Facade sub-frame for cassettes and panels is based on Omega (Ω), C, and Z-sections made of S235 or S350GD+Z275 steel, fastened to the container’s structural posts via PA plastic thermal isolators (thermal bridge break). The Ω-section serves as a horizontal and vertical grid: t=1,0–2,0 mm, h=40–80 mm, axial spacing ≤800 mm according to calculations per PN-EN 1991-1-4 (wind loads).
For ventilated facades with flat or trapezoidal sheet cladding, C-sections (h=50–80 mm, t=1,5 mm) are used as intermediate rails. Z-sections are applied in sandwich facade systems, where the cladding sheet is fastened from the outside, and the foot of the Z-profile is attached directly to the container wall.
Profil Z
Profil C
Profil Ω
Advanced CNC prefabrication services for the container industry
Cold-forming technology (CNC) is the stage where the cold-rolled container profile takes its final shape. Unlike the production of hot-rolled structural profiles, where any holes or technological cuts require separate operations after purchase, container profiles produced on a roll-forming machine or a CNC press brake leave the facility with all holes and notches pre-cut, fully ready for bolt-on assembly.
Precision custom punching, beveling, and technological notches
In container manufacturing, standard CNC processes comprise:
- Punching: round holes (φ10–60 mm), oval holes (for container transport/lifting), and square holes
- Notching and Beveling): corner profile notches with a depth of 20–50 mm for frame corner shaping and elimination of lap-joint collisions; beveling angles of 30°–60°
- Edge Flanging/Forming (Wywinięcie krawędzi): forming profile ends at specific angles to facilitate the assembly of remaining container components
- Laser Cutting: edge roughness Ra ≤12,5 μm (Class K1 according to PN-EN ISO 9013)
Thanks to CNC cold-forming technology, the assembly time for a 20 ft container frame on-site is reduced to approximately 3–4 hours using bolt-on technology. The elimination of welding removes the need for certified welders and avoids high-temperature zones that would otherwise destroy the protective zinc coating.
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Manufacturing Technologies: Press Brake Bending and Continuous Roll Forming
The production of container profiles is carried out using two complementary methods:”
1. Continuous Roll-Forming: Dedicated to profiles with a constant cross-section and lengths exceeding 6 meters. The line speed is approximately 40 m/min, integrated in-line cutting and punching. Ideal for C and Z-profiles in production runs exceeding 500 linear meters.”
2. CNC Press-Brake Bending: Designed for profiles with variable geometry, corners, facade cassettes, and flashings. Featuring a pressing force of 100–300T, a bed length of up to 8 meters. This method allows for the fabrication of most custom shapes from sheet metal with thicknesses ranging from t=0,5–4,0 mm.
Both processes are carried out under the PN-EN 1090 system, ensuring full material traceability (Type 3.1 certificate according to EN 10204), dimensional documentation, and batch repeatability. Every profile leaving the production facility bears a marking that includes the steel grade, heat number, dimensions, and EXC execution class.
Technical Comparison: ISO Shipping Container vs. Office Container
| Parameter | Shipping / Offshore Container | Office / Residential Container |
| Steel Grade | S350GD / S390GD + Zinc-Magnesium (e.g.: ZM310 | S235 / S350+Z275 |
| Anticorrosion Coating | Zinc-Magnesium (Class C5-M, 2000h Salt Spray Test ISO 9227) | Zinc Galvanized Z275 g/m² (class C2/C3) |
| Column Profile Height | h > 250 mm, steel thicknes t=3,0–4,0 mm | h=150–200 mm, steel thickness t=2,0–4,0 mm |
| 20 ft Frame Weight | ~2,5–3,0 t (25% weight reduction vs. hot-rolled) | ~2,0–2,5 t |
| Execution Standards | PN-EN 1090-2 (EXC4), ISO 1496-1 | PN-EN 1090-2 (EXC3) |
| Wind Load Design | 2,5 kN/m², marine/offshore environment | 1,5 kN/m², moderate inland environment |
The selection of material grades and geometric parameters must be strictly derived from structural calculations according to PN-EN 1993-1-3 (Design of steel structures – General rules – Supplementary rules for cold-formed members and sheeting), taking into account the specific environmental conditions of the site.
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