A rectangular hollow section is similar to a square hollow section (also known as a box section) and thin wall tube. It is actually made from a round tube that is formed through multiple stages of forming dies.
Rectangular hollow section or RHS is used for various purposes throughout industry, from frameworks including buildings, to supporting brackets in industrial applications. Anywhere a strong, lightweight and easy-to-manufacture fabrication is needed, RHS can often be utilized.
RHS comes in a wide range of sizes, from 20x10mm to 400x200mm, with wall thicknesses ranging from 1.5mm to 12.5mm. It is defined simply by the two width measurements across the flat sides.
The ratio of width to height of the section is not fixed, for example: 50×20, 50×25, 50×30 and 50×40 are all readily available sizes, giving a large range of options in your design.
As well as the overall section size, wall thickness has a large bearing on load capacity. A larger wall thickness helps with bending loads, such as in a beam configuration, and torsional rigidity, too.
In addition to increasing strength, a thicker wall can allow for larger welds and features such as tapped holes.
RHS wall thickness ranges from 1.5mm to over 12.5mm, with the available thicknesses scaling with the overall size. For instance, the thinnest wall in 40×20 would be 1.5mm, but the thinnest wall available in 150x50mm is 3mm.
The most common grades of rectangular hollow section are ASTM A500 and A513. A500 is a cold-formed, high-strength structural material.
A513 is an ERW tube, made using thin sheets of steel. It is not typically used for structural applications and has a generally under 2mm wall thickness.
The tolerances of A513 are typically better than those of A500. The dimensional tolerances for cold-formed rectangular hollow sections are listed in the table below.
| Largest Outside Dimension (in) | +/- |
|---|---|
| 2-1/2″ and under | 0.020 |
| 2-1/2″ to 3-1/2″ | 0.025 |
| 3-1/2″ to 5-1/2″ | 0.030 |
| 5-1/2″ and above | 1% |
There are numerous considerations when selecting a material for your project, these include:
In many cases, cost is the largest factor in engineering projects; thankfully, RHS is a cost-effective option in both material and production costs.
Steel is likely the best option, as it is by far the cheapest, but consider the additional costs of corrosion protection. Pre-galvanized RHS is available, but presents issues if welding is needed.
The larger the sections and the thicker the walls are, the stronger the material will be. This naturally needs balancing to the overall weight and form factor of the part required.
In many cases, increasing the overall section size, with a relatively thin-walled tube, gives a good strength-to-weight ratio, compared to a smaller section with a thicker wall.
Whether you need mild steel, galvanized steel, stainless or aluminum, Metals Supermarket has it in stock, in a massive range of sizes. As well as a nationwide delivery available, a cut-to-length service can save you time and money on your project.
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