# Comparing Square vs Round Tubing Strength | Help Understanding

• madison069
In summary, the conversation discusses the strength comparison between square and round tubing. The maximum stress in a beam is calculated for both types of tubing, with the round tubing having a higher maximum stress. However, it is noted that circular tubing has equal stress regardless of load direction, while square tubing may weaken at off-axis loads. The moment of inertia is also mentioned as a factor in comparing the strength of the two types of tubing.
madison069
I've been trying to determine which is stronger, square tubing or Round tubing. I searched the forum but came up with some other ideas but not the answer.

Using a Square tubing that's 2"x2" AND .25" thick vs. a Round Tubing that's 2" outside diameter and 1.5" inside Diameter and both are 5' long, as my example. My Force is 4,000 lbs.

I calculated the Maximum Stress in a beam with uniform support at the ends, and my Force in the middle of the beam. My numbers are M.S. for Square tubing is 13,713.66 psi and M.S. for Round tubing is 23,325.24 psi.

Does this mean that the Square tubing is stronger then the Round tubing? Or am I misunderstanding the definition of Maximum Stress. Also why is it I hear Round tubing is Stronger then Square tubing?

One nice thing about circular tubing is that the stress is equal independent of the load direction.

Let's walk through it though. The strength of a beam is a function of its area moment of inertia
http://en.wikipedia.org/wiki/Second_moment_of_area

The moment of inertia for a (let's assume solid for the moment) circle is:
$$I_0 = \frac{\pi}{4}r^4$$
And the moment of inertia for a rectangle about its centerline (not diagonal) is:
$$I_x = \frac{bh^3}{12}$$
Let's now assume that for comparison, the two sections have the same area, and thus the same weight. For ease of comparison, let's also assume that the rectangular tubing is square. Then to find the length of one side, a, of the sqaure:
$$\begin{split} A = &\pi r^2 \\ &\pi r^2 = a^2 \\ a = \sqrt{\pi r^2} \end{split}$$
b and h both equal, so the moment of inertia of the square section is:
$$\begin{split} I_x &= \frac{\sqrt{\pi r^2}(\sqrt{\pi r^2})^3}{12} \\ I_x &= \frac{ (\sqrt{\pi r^2})^4}{12} \\ I_x &= \frac{ (\pi r^2)^2}{12} \\ I_x &= \frac{ \pi^2 r^4}{12} \\ I_x &= \frac{\pi^2}{12}r^4 \end{split}$$
One can now compare the two coefficients, and see which is larger:
$$\frac{\pi^2}{12} = 0.822 > \frac{\pi}{4} = 0.785$$

So, based on this, a square tubing is 4.6% stronger for the same weight than circular. However, as the loading starts to go off axis, the square tubing will get much weaker. I'll let you determine the moment of inertia at a full 45° off axis.

p.s. Might want to check my work before taking it as gospel though

Thanks, I'll work on it and get back with you on my findings.

## What is the difference between square and round tubing?

Square tubing has four sides and a flat surface, while round tubing is circular. This means that square tubing is more rigid and resistant to twisting, while round tubing is better at withstanding external pressure.

## Which type of tubing is stronger?

It depends on the specific application and design. Generally, square tubing is stronger in terms of resistance to bending and twisting, while round tubing is better at resisting compression. However, the strength of each type can also vary depending on the material, wall thickness, and other factors.

## Can square tubing be used interchangeably with round tubing?

No, square and round tubing have different structural properties and cannot be used interchangeably without proper analysis and design considerations. Using the wrong type of tubing can compromise the structural integrity and safety of a project.

## What factors affect the strength of square and round tubing?

The strength of square and round tubing can be affected by the material used, the wall thickness, the length and diameter of the tubing, and the type of load or stress it is subjected to. Other factors such as temperature, corrosion, and surface finish can also play a role.

## How can I determine the strength of square and round tubing for my project?

To determine the strength of square and round tubing, it is important to consult structural engineering principles and use relevant calculations, formulas, and testing methods. It is also recommended to seek professional guidance and follow industry standards and codes for proper design and safety.

### Similar threads

• General Engineering
Replies
8
Views
2K
• General Engineering
Replies
11
Views
6K
• General Engineering
Replies
4
Views
17K
• General Engineering
Replies
6
Views
4K
• General Engineering
Replies
5
Views
10K
• General Engineering
Replies
2
Views
3K
• Mechanical Engineering
Replies
18
Views
1K
• Mechanical Engineering
Replies
1
Views
2K
• Mechanical Engineering
Replies
7
Views
44K
• Mechanical Engineering
Replies
16
Views
1K