# How to calculate section modulus of channel section

• Mech King
In summary, the conversation discusses calculating the section modulus of a channel section for bending calculations. The value provided on the data sheet has values for section modulus in both the X and Y axis, but the person believes they should only use the section mod value where the load is perpendicular to its axis. The conversation also mentions calculating this value from scratch and how it differs for symmetrical and non-symmetrical cross-sections. The person providing assistance suggests using the bottom section modulus for tension and the top section modulus for compression stresses. The conversation ends with a thank you for the clarification and a note that the section modulus is needed for bending moments.
Mech King
Hi guys,

I am trying to calculate the section modulus of some channel section. I was going to use the value provided on the data sheet but its confusing me because it has values of section modulus in the X and Y axis. Am i right in assuming that i use section mod value where the load is perpendicular to its axis?

Also how would you calculate this value from scratch. I am familiar with calculating the section modulus of a sections that are symetrical in two axis, but not with those in one.

Any help would be much appreciated.

Cheers,

Amir

Last edited:
You are doing bending calculations right?

Yes you would be interested in the section modulus of the axis perpendicular to the load.

Also the section modulus of the top and bottom of the channel (on the same axis) will be different if the cross-section isn't symmetrical about that axis (the neutral axis won't be in the center of the cross section). If you are putting a load on the top and creating bending moments, then you would use the bottom section modulus to check tension and the top section modulus to check compression stresses.

Theres some info there (though its a bit short) explaining it:

http://en.wikipedia.org/wiki/Section_modulus

Thanks very much for the clarification elterrible, much appreciated.

Yes its for a bending moment, i haven't really worked with beams that are symetrical in one plane only so was a bit unsure. Thanks for your help,

Cheers

Amir

## 1. How do you calculate section modulus of a channel section?

To calculate the section modulus of a channel section, you will need to know the dimensions of the channel section, including the height, width, and thickness. The formula for calculating the section modulus is Z = I/c, where Z is the section modulus, I is the moment of inertia, and c is the distance from the neutral axis to the outermost point of the section.

## 2. What is the formula for calculating moment of inertia?

The moment of inertia for a channel section can be calculated using the formula I = (1/12)(b)(h^3) + (b)(t)((h/2)^2), where b is the width of the channel, h is the height of the channel, and t is the thickness of the channel.

## 3. How do you determine the distance from the neutral axis to the outermost point of a channel section?

The distance from the neutral axis to the outermost point of a channel section can be determined by dividing the height of the channel by 2. This is because the neutral axis always passes through the centroid of the section, which is located at the halfway point of the height of the channel.

## 4. Can the section modulus of a channel section be negative?

No, the section modulus of a channel section cannot be negative. It is a measure of the strength and stiffness of a section, and a negative value would indicate that the section is not able to resist bending forces.

## 5. Is the section modulus the same as the moment of inertia?

No, the section modulus and moment of inertia are two different properties of a section. The moment of inertia is a measure of the distribution of mass around a section's neutral axis, while the section modulus is a measure of its resistance to bending. However, the section modulus does depend on the moment of inertia, as shown in the formula Z = I/c.

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