Rectangular hollow section (RHS) steel is a versatile structural product used extensively in construction, fabrication, and engineering projects. Understanding the weight of rectangular hollow section steel is essential for structural design, material procurement, cost estimation, and transportation planning. The weight of RHS steel tubing is calculated using the standard steel weight formula, which multiplies the unit weight of steel by the volume of the section. Given that steel has a density of 7,850 kg/m³, the calculation requires determining the cross-sectional area of the hollow profile and multiplying it by the length. Whether you are designing a steel frame, selecting materials for a building project, or preparing a bill of quantities, knowing how to compute RHS weights accurately will save time and reduce material wastage. For engineers who also work with solid bars, reading A Guide On How To Calculate Weight Of Steel Bars provides helpful parallels between solid and hollow section calculations.
Understanding Rectangular Hollow Section Steel
Rectangular hollow section steel is manufactured by heating a flat steel plate and molding it into a rectangular tubular shape. The edges are refined and welded to produce a seamless or welded hollow profile. This fabrication method creates a product that combines high tensile strength with a relatively low self-weight, making it ideal for applications where structural efficiency matters. RHS steel is classified as a type of mild steel bar and shares the same material density of 7,850 kg/m³ with other steel products.
The dimensions of RHS are defined by three parameters: the longer side dimension (A), the shorter side dimension (B), and the wall thickness (t). These dimensions are expressed in millimetres and are available in a broad range. The minimum lateral dimension typically available is 26 mm × 13 mm, while the maximum reaches up to 400 mm × 200 mm. Wall thicknesses range from a minimum of 0.8 mm up to 12 mm, and lengths can vary from 6 metres to 12 metres depending on the manufacturer and application. Square hollow sections (SHS) follow a similar specification but have equal side dimensions, starting from 12 mm × 12 mm and going up to 300 mm × 300 mm. Proper detailing of connections is critical when using these sections in structural frames, and the principles outlined in Typical Joint Detailing Of Steel Hollow Sections offer valuable guidance for safe and efficient joint design.
Why Rectangular Hollow Sections Are Preferred Over Circular Sections
In many steelwork applications, rectangular and square hollow sections have become more popular than their circular counterparts. The primary reason lies in the ease of connection and fabrication. Flat surfaces on RHS members allow for simpler bolted and welded connections without the need for curved gusset plates or special profiling. This translates directly to reduced labour costs and faster erection times on site. Additionally, rectangular sections offer greater flexibility in architectural design because they can be integrated more easily into walls, ceilings, and other building elements without protruding curves.
Another factor driving the adoption of RHS is the superior torsional stiffness compared to open sections such as I-beams and channels. While circular hollow sections offer the best torsional resistance, rectangular sections provide a practical balance between torsional performance and connection simplicity. The flat faces also simplify the attachment of cladding, bracing, and secondary steelwork. For a detailed comparison of why square and rectangular sections have gained such widespread acceptance, refer to Why Does Square Hollow Section Become More Popular Than Circular Hollow Section In Steelworks.Html. This external resource examines the engineering and practical reasons behind the shift in industry preference.
How to Calculate the Weight of RHS Steel
The weight of a rectangular hollow section is determined using the fundamental relationship: weight equals volume multiplied by density. The volume of the hollow section is calculated by subtracting the inner void area from the outer cross-sectional area and then multiplying by the length. The formula can be expressed as follows:
Steel weight formula: Weight = Unit Weight of Steel × Volume of Steel
For a worked example, consider an RHS with the following dimensions:
- Side length of surface A = 100 mm (0.1 m)
- Side length of surface B = 50 mm (0.05 m)
- Wall thickness t = 10 mm (0.01 m)
- Length L = 1 m
The total volume Vt is the sum of the volumes of the four walls:
Vt = 2(A × t × L) + 2((B − 2t) × t × L)
Vt = 2(0.1 × 0.01 × 1) + 2((0.05 − 0.02) × 0.01 × 1)
Vt = 0.002 + 0.0006 = 0.0026 m³
Weight = 0.0026 × 7,850 = 20.41 kg per metre
This calculation method applies to any RHS size. Engineers can also use RHS weight calculators or steel weight calculators available online to speed up the process for multiple sections. For a broader understanding of how weight calculations apply across different steel bar shapes, How To Calculate Weight Of Steel Bars covers round, square, and flat bars with practical examples.
Standard Sizes and Unit Weights of Rectangular Hollow Sections
Manufacturers produce RHS steel in standardized dimensions to ensure consistency across projects. The following table presents common rectangular hollow section sizes along with their approximate weights per metre length. These values are based on a steel density of 7,850 kg/m³ and are typical of commercially available sections.
| Outer Dimensions (mm) | Wall Thickness (mm) | Weight per Metre (kg/m) |
|---|---|---|
| 50 × 25 | 2.0 | 2.18 |
| 60 × 40 | 2.5 | 3.57 |
| 80 × 40 | 3.0 | 5.19 |
| 100 × 50 | 3.0 | 6.60 |
| 100 × 60 | 4.0 | 9.14 |
| 120 × 60 | 4.0 | 10.52 |
| 150 × 100 | 5.0 | 18.19 |
| 200 × 100 | 6.0 | 26.39 |
| 250 × 150 | 8.0 | 47.12 |
| 300 × 200 | 10.0 | 72.27 |
These values serve as a useful reference during the preliminary design phase. However, exact weights should always be verified against the manufacturer’s technical data sheet, as slight variations in corner radii and manufacturing tolerances can affect the final weight. For a complete set of formulas covering steel, aluminum, brass, and copper sections, Weight Calculation Formulas For Construction Materials Steel Aluminum Brass And Copper provides a comprehensive reference for multi-material projects.
Practical Applications Across Industries
Rectangular hollow section steel is widely used across multiple industries due to its favourable strength-to-weight ratio and ease of fabrication. In the construction sector, RHS members serve as columns, beams, roof trusses, and bracing elements in steel-framed buildings and industrial warehouses. The flat surfaces simplify the attachment of wall panels, roofing sheets, and mezzanine floors, making them a preferred choice for pre-engineered buildings.
In the automotive and machinery industries, RHS is used to fabricate chassis components, equipment frames, conveyor supports, and guardrails. Shipbuilding applications include deck structures, handrails, and internal framing where corrosion-resistant grades are specified. Electrical engineering and power plant projects also rely on RHS for cable trays, support structures, and equipment mounting frames. Understanding the full range of standard profiles available can help designers select the most efficient section for each application. Rolled Steel Sections offers a broader overview of the various steel section types and their typical uses in structural engineering.
Evaluating the Benefits and Drawbacks of RHS Steel
Like any structural material, rectangular hollow section steel has distinct advantages and limitations that engineers must consider during the design process.
Advantages:
- RHS sections provide greater design flexibility compared to open sections, enabling architects and engineers to create lightweight yet visually appealing structures.
- The higher strength-to-weight ratio of hollow sections reduces the overall dead load on foundations and supporting elements, leading to material savings and lower construction costs.
- The closed cross-section offers excellent torsional resistance, making RHS well suited for members subjected to twisting forces.
- Clean, flat surfaces simplify welding, bolting, and cladding attachment, reducing fabrication time and labour expenses.
Disadvantages:
- Hollow sections are susceptible to corrosion, particularly in exposed or humid environments. Proper surface protection through galvanizing or paint systems is essential for long-term durability.
- RHS members cannot fully resist weathering agents on their own and require protective coatings when used in outdoor applications.
- For very large structures, the unit cost of hollow sections may be higher than that of open sections, potentially affecting the overall project budget.
- Rectangular hollow sections have lower load-bearing capacity for a given cross-sectional area compared to solid sections, making them less suitable for applications involving extremely heavy loads.
Conclusion
Rectangular hollow section steel is a highly efficient structural product that combines strength, light weight, and ease of fabrication. The ability to calculate its weight accurately using the standard steel weight formula is a fundamental skill for structural engineers, quantity surveyors, and construction professionals. By understanding the relationship between dimensions, wall thickness, and unit weight, design teams can optimize material selection, reduce waste, and improve cost control on any project. Whether used in building frames, industrial machinery, or infrastructure works, RHS steel continues to be a reliable choice for modern construction. For professionals working with concrete as well as steel, the design principles discussed in Rectangular Concrete Beams provide useful comparisons between steel and concrete member design approaches.