Steel hollow sections are commonly used in construction and come in various standard sizes. These sections are categorized into two main types: rectangular hollow sections (RHS) and circular hollow sections (CHS), with square hollow sections (SHS) being a subset of RHS.

1. Rectangular Hollow Sections (RHS):

   • Width x Height: Typically range from 50x25 mm to 400x300 mm.
   • Wall Thickness: Varies from 2 mm to 16 mm.
   • Length: Standard lengths are usually 6 meters or 12 meters, but custom lengths can be ordered.

2. Square Hollow Sections (SHS):

   • Side Length: Common sizes range from 20x20 mm to 400x400 mm.
   • Wall Thickness: Ranges from 2 mm to 16 mm.
   • Length: Standard lengths are similar to RHS, typically 6 meters or 12 meters.

3. Circular Hollow Sections (CHS):

   • Diameter: Sizes range from 21.3 mm to 508 mm.
   • Wall Thickness: Varies from 2 mm to 20 mm.
   • Length: Standard lengths are generally 6 meters or 12 meters.

These sizes can vary slightly depending on regional standards and manufacturers. The dimensions are typically specified according to standards such as the European Standard EN 10210, the American Standard ASTM A500, or the British Standard BS EN 10219. These standards ensure consistency in the mechanical properties and dimensions of the hollow sections, making them suitable for structural applications.

To calculate the weight of a steel hollow section, follow these steps:

1. Identify Dimensions: Determine the outer dimensions (width, height, and length) and the wall thickness of the hollow section. For a rectangular or square section, note the outer width (W), outer height (H), and wall thickness (t). For a circular section, note the outer diameter (D) and wall thickness (t).

2. Calculate Cross-Sectional Area:

   • Rectangular/Square Section:
     • Outer area = W × H
     • Inner dimensions = (W - 2t) × (H - 2t)
     • Inner area = (W - 2t) × (H - 2t)
     • Cross-sectional area = Outer area - Inner area
   • Circular Section:
     • Outer area = π × (D/2)^2
     • Inner diameter = D - 2t
     • Inner area = π × ((D - 2t)/2)^2
     • Cross-sectional area = Outer area - Inner area

3. Calculate Volume: Multiply the cross-sectional area by the length (L) of the hollow section to get the volume.

4. Determine Density: Use the density of steel, typically 7850 kg/m³.

5. Calculate Weight: Multiply the volume by the density to get the weight.

Formula for weight:

• Rectangular/Square: Weight = [(W × H - (W - 2t) × (H - 2t)) × L] × Density
• Circular: Weight = [π × ((D/2)^2 - ((D - 2t)/2)^2) × L] × Density

This will give you the weight of the steel hollow section in kilograms.

Steel hollow sections offer several advantages in construction:

1. Strength and Durability: Steel hollow sections provide high strength-to-weight ratios, making them ideal for structural applications. They can withstand significant loads and stresses, ensuring long-term durability.

2. Lightweight: Compared to solid steel sections, hollow sections are lighter, which reduces the overall weight of the structure. This can lead to cost savings in transportation and foundation requirements.

3. Versatility: Available in various shapes such as square, rectangular, and circular, steel hollow sections can be used in diverse applications, from columns and beams to trusses and frames.

4. Aesthetic Appeal: The clean lines and smooth surfaces of hollow sections contribute to modern architectural designs, offering an aesthetically pleasing appearance.

5. Ease of Fabrication and Installation: Hollow sections are easy to cut, weld, and join, facilitating quick and efficient construction processes. Their uniform shape simplifies alignment and assembly.

6. Cost-Effectiveness: The reduced weight and ease of handling can lower labor and transportation costs. Additionally, the efficient use of material in hollow sections can lead to savings in raw material costs.

7. Fire Resistance: Steel hollow sections can be treated with fire-resistant coatings, enhancing their performance in fire-prone environments.

8. Corrosion Resistance: When properly coated or galvanized, steel hollow sections offer excellent resistance to corrosion, extending the lifespan of the structure.

9. Sustainability: Steel is recyclable, and using hollow sections can contribute to sustainable construction practices by reducing material waste and enabling the reuse of steel.

10. Seismic Performance: The inherent flexibility and strength of steel hollow sections make them suitable for structures in seismic zones, as they can absorb and dissipate energy during an earthquake.

Steel hollow sections can be joined or connected using several methods, each suited to specific applications and requirements:

1. Welding:

   • MIG/TIG Welding: Suitable for thin-walled sections, providing clean and precise joints.
   • Arc Welding: Common for thicker sections, offering strong and durable connections.
   • Spot Welding: Used for joining overlapping sections, especially in sheet metal applications.

2. Bolting:

   • Flange Connections: Flanges are welded to the ends of the sections and bolted together, allowing for easy disassembly.
   • Cleats and Gussets: Plates are welded to the sections, and bolts are used to connect these plates, providing flexibility and ease of maintenance.

3. Riveting:

   • Used less frequently in modern construction but still applicable for certain structural applications where welding is not feasible.

4. Mechanical Fasteners:

   • Self-Drilling Screws: Used for lighter applications, providing quick and easy assembly.
   • Blind Rivets: Suitable for applications where access is only available from one side.

5. Adhesive Bonding:

   • Structural adhesives can be used for non-load-bearing applications or where welding and mechanical fasteners are not suitable.

6. Interlocking Systems:

   • Prefabricated systems that allow sections to be snapped or slotted together, often used in modular construction.

7. Sleeve Joints:

   • A sleeve or coupler is used to connect two sections, often employed in temporary structures or scaffolding.

Each method has its advantages and limitations, and the choice depends on factors such as load requirements, environmental conditions, ease of assembly, and cost considerations.

Hot-rolled steel hollow sections are produced by heating steel above its recrystallization temperature and then shaping it into the desired form. This process allows for the creation of larger and thicker sections with uniform mechanical properties. Hot-rolled sections typically have a rougher surface finish and are more suitable for applications where precise dimensions are not critical. They are often used in construction, infrastructure, and heavy machinery due to their strength and durability.

Cold-formed steel hollow sections, on the other hand, are made by bending and shaping steel at room temperature. This process results in a smoother surface finish and more precise dimensions, making them ideal for applications requiring tight tolerances and aesthetic appeal. Cold-forming increases the yield strength of the steel due to strain hardening, but it may also introduce residual stresses. These sections are commonly used in lightweight structures, automotive components, and furniture.

In summary, the main differences lie in the manufacturing process, surface finish, dimensional precision, and typical applications. Hot-rolled sections are better for heavy-duty applications, while cold-formed sections are preferred for precision and aesthetic purposes.