Rectangular tube vs. Square tube: Which has a better load-bearing capacity?

Rectangular vs. Square Tubes: Which Has Better Load-Bearing Capacity?

For most applications where the material is used as a beam (bending), rectangular tubes offer better and more efficient load-bearing capacity. However, for applications where the material is used as a column (bearing compression), both have their advantages and disadvantages.

The choice between rectangular and square tubes primarily depends on the direction of the load.

If primarily subjected to bending: Rectangular tubes are superior.
If primarily subjected to axial compression: Square tubes are more stable, but high-strength rectangular tubes can also perform well in specific directions.

For isotropic loads or torques: Square tubes are superior.

Features of rectangular tubes:
Rectangular tubes have higher bending strength and stability, which makes them more suitable for situations where they carry large loads or need to resist bending moments and torques. The structural design of rectangular tubes generally handles shear and bending stresses better, making them a better choice in applications where large horizontal or bending forces are required.

Features of square tubes:

The cross-sectional shape of square tubes is more stable and is suitable for scenes that need to withstand large vertical loads. They also have advantages in situations that need to resist shear forces because their cross-sectional areas are usually larger than rectangular tubes and can better disperse shear forces. The production of square tubes is relatively simple and has a wide range of applications.

Comparison of bending strength of rectangular tube and square tube:

1. Definition of bending strength

Flexural strength is defined as the maximum load-bearing capacity of a material under bending load. The higher the bending strength, the better the durability and the longer the service life of the material.

When a material is used as a beam (e.g., support, crossbeam), its resistance to bending is mainly determined by its section modulus. The larger the section modulus, the stronger the bending resistance.

2. Comparison of bending strength of rectangular tube and square tube

The strength behavior of rectangular tubes and square tubes under bending loads is different. Generally speaking, the bending strength of rectangular tubes of the same material and size is higher than that of square tubes. This is because the strength distribution of the rectangular tube is more uniform, and its moment of inertia and bending section coefficient are larger than that of the square tube with the same cross-sectional area.

Cause Analysis:

When a material is subjected to bending, the further away from the central axis, the greater the contribution to bending resistance. Rectangular tubes significantly increase their section modulus by distributing more material along the top and bottom surfaces of their longer sides.

Comparison of compressive strength of rectangular tube and square tube:

1. Definition of compressive strength

Compressive strength refers to the ability of a material to resist damage when subjected to compressive loading. The higher the compressive strength, the harder and tougher the material is and its greater load-bearing capacity.

When used as a material for columns (e.g., supports, pillars), its load-bearing capacity primarily depends on:
a. Cross-sectional area: The larger the area, the greater the pressure it can withstand.
b. Slenderness ratio and stability: The slenderer the column, the more prone it is to buckling (instability) and failure, rather than being crushed.

2. Comparison of compressive strength of rectangular tube and square tube

The compressive strength of rectangular tubes and square tubes is not much different. This is because the strength distribution of rectangular tubes and square tubes is basically the same under compressive load. When subjected to the same load, the strength performance of the two steel tubes is also similar.

Cause Analysis:
Square tubes: Have identical radii of inertia along both principal axes (X-axis and Y-axis), meaning their buckling resistance is the same in all directions, resulting in excellent stability. This is a significant advantage for compression conditions with uncertain orientation (such as building pillars).
Rectangular tubes: Have different radii of inertia along the two principal axes. They exhibit excellent stability under compression along the longer side, but poor stability and are prone to buckling under compression along the shorter side.

Conclusion:

The strength performance of rectangular tubes and square tubes varies under different forces. The bending strength of rectangular tubes of the same material and size is higher than that of square tubes, but under compressive load, the strength difference between rectangular tubes and square tubes is not significant. When selecting steel pipes, practical application needs and design requirements should be comprehensively considered, and steel pipes of appropriate materials and cross-sectional shapes should be selected.

Tips: ASTM A500 is a standard specification for cold-formed welded and seamless carbon steel structural tubing in round, square tube and rectangular tube shapes.

ASTM A500 steel pipes can be subjected to most of the usual fabricating operations. Ductility is good. It bends well, flattens, cuts, punches, flares and flanges easily, and can be welded by the commonly-used techniques and practices.

Read more: How to Correctly Measure Square Tube Size?