Exploring the Strength-to-Weight Ratio of Square Steel Tubing

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From buildings and cars to big industrial machines, square steel tubing is one of the most popular shapes for building support structures. Also known as hollow structural section (HSS) tubing, this shape provides lightweight qualities that wouldn’t be possible with a solid material. 

In fact, the strength-to-weight ratio of square steel tubing is superior to most other shapes used in engineering and construction. Still, there are differences between various square steel tubes. A tubing with a high strength-to-weight ratio can support heavy loads while remaining lightweight, making it crucial in industries like aerospace, automotive, and building skyscrapers.

In this article, we will explore the strength-to-weight ratio of square steel tubing, particularly things like the type of material used in various applications and calculating the strength-to-weight ratio.

Strength-to-Weight Ratio and Different Material Properties

The strength-to-weight ratio is defined as the amount of strength of a material relative to its weight and is calculated by dividing the material’s tensile or compressive strength by its density.

Several things can play a factor in the strength-to-weight ratio of square steel tubing. Namely, the cross-sectional dimensions, like the thickness of the walls and overall dimensions, will significantly impact the weight and strength of the square tubing.

However, the biggest factor is definitely the choice of material. The type of steel used can significantly alter the density and tensile properties of the part, thus affecting the ratio.

Carbon steel is the most commonly used material for square steel tubing, thanks to its excellent strength and affordability. It’s not the lightest around, but due to its strength, it can be used for tubing with thinner walls. However, carbon steel is very corrosive, so in implementations where corrosion resistance is necessary, like parts exposed to moisture, salt water, or chemicals, stainless steel is preferred. 

More advanced alloy steels with chromium, nickel, and molybdenum will also have increased strength, lower density, and higher corrosion resistance. However, these alloys are often very expensive and out of reach for most projects.

Aluminum is a good alternative for projects where lightness is crucial, though square aluminum tubing usually has a lower tensile strength than steel. Wood is also lighter than steel but, again, lacks strength and durability.

Benefits of High Strength-to-Weight Ratio

Square steel tubing provides an excellent strength-to-weight ratio because it’s hollow inside. Thus, it can support very heavy loads with a minimal effect on the overall weight of the structure. Thanks to this structural efficiency, it is widely used for high-rise buildings, aircraft, and automobiles. 

Furthermore, square steel tubing is easy to handle and construct with widespread techniques like welding and bolting, making it less labor-intensive. This also makes it very easy to transport, as the parts can be smaller and then constructed on-site. In addition, the high strength-to-weight ratio results in long-term cost savings despite the higher initial cost.

Because square steel tubing can be fabricated into various shapes and sizes, it’s also very versatile, i.e., fit for projects that require a sleeker, modern form.

How to Calculate the Strength-to-Weight Ratio?

The strength-to-weight ratio can be expressed in the simple formula:

Strength-to-Weight Ratio = Strength / Weight

Here, strength would be in units of force, such as Newtons (metric) or pounds-force (imperial). It can refer to various types of strength, though, including tensile strength, yield strength, or compressive strength.

Meanwhile, the weight would be in units such as kilograms (metric) or pounds (imperial).

Example calculation

Say we want to calculate the strength-to-weight ratio of square steel tubing with the following properties:

• Tensile Strength: 400 MPa (Megapascals)
• Density: 7,850 kg/m³
• Dimensions: 50 mm x 50 mm cross-section with a wall thickness of 3 mm

Cross-Sectional Area Calculation:

A = (outer side length)^2 – (inner side length)^2

Conversion to Square Meters:

A = 564 * 10^-6 m^2

Volume per Meter Length Calculation:

V = A * length

V = 564 * 10^-6 m^2 * 1 m = 564 * 10^-6 m^3

Weight per Meter Calculation:

W = V * density

W = 564 * 10^-6 m^3 * 7,850 kg/m^3 = 4.43 kg

Strength-to-Weight Ratio Calculation:

Strength-to-Weight Ratio = Tensile Strength / Weight per meter

Strength-to-Weight Ratio = 400 MPa / 4.43 kg/m

Conversion of MPa to N/m²:

400 MPa = 400 * 10^6 N/m^2

Final Strength-to-Weight Ratio

Strength-to-Weight Ratio = (400 * 10^6 N/m^2) / (4.43 kg/m) = 90.3 * 10^6 N/kg

Please note that this should only serve as an example of how to calculate the ratio. We strongly advise consulting a professional before doing any calculations.

Using Software

For quick calculations, we would recommend online calculators, such as MatWeb or Engineering Toolbox. Meanwhile, programs like ANSYS, SolidWorks Simulation, and Autodesk Fusion 360 can significantly speed up the calculation process. Crucially, they can directly analyze the strength-to-weight ratio under various loading conditions. If you want to include the material properties, AutoCAD or Inventor can help you simulate different square tubing designs under various loads and optimize the part according to the steel properties.

How to Enhance the Ratio?

Various treatments and manufacturing techniques can significantly improve the strength-to-weight ratio of square steel tubing. Notably, hydroforming and roll forming enhance structural integrity while creating minimal waste. 

Cold drawing and rolling also increase the strength of steel by deforming it at room temperature. Meanwhile, advanced welding techniques, like laser welding and friction stir welding, ensure strong joints, leading to higher overall frame strength.

Furthermore, heat treatments are often applied to steel to improve its mechanical properties. For instance, quenching, tempering, and annealing can increase the strength and toughness by changing the microstructure of the material. Still, in some situations, alloying is required to enhance the mechanical properties of steel, which includes adding elements like chromium, nickel, molybdenum, and vanadium.

The cross-section design can also affect the strength. For instance, using thinner walls with reinforced corners can provide the necessary strength without adding excessive weight. Using advanced computer software, you can also optimize the distribution of material, i.e., make square steel tubes that aren’t subjected to big loads slightly thinner.

Ashton Henning