Section Modulus Calculation

[DeePamn]

Good Afternoon,

I have been browsing the forum for a number of months and now I have decided to create an account, to further my knowledge and pass on what I currently understand.

I have a question which may be simple to someone but currently driving me up the wall.

It is about calculating section modulus's (moments of intertia) for a circular hollow section with a sector removed. From reading roarks forumulas for stress and strain I don't seem to be able to find a solution to my question.

I understand it is not as simple as calculating the moment of inertia of a circular hollow section and then subtracting the sector section.

Does anyone have an idea of how to calculate the moment of inertia of a circular hollow section with a sector removed?

Thanks to replies in advance.

 

[robyengIT]

The easiest way is Autocad.
1 - 1st draw the figure you want (scale 1:1)
2 - transform the figure in a region
3 - then check the mass property and you will have : area,perimeter, center of gravity, inertia moduli with reference to the axxis of the center of gravity or to another one

Regards

 

[DeePamn]

Thanks for your reply robyengIT.

I had got so involved in trying to calculate the section properties I completely forgot about using autoCAD to find the section properties.

 

[Agent666]

It is as simple as you state as long as you adjust the moment of inertia to the final centroid based on using the parallel axis theorem. You of course need to know the centroid of the remaining hollow section, which depending on the configuration is quite easy if you know the centroid of a section of the wall based on the angle from the centre or the length of wall around the curve. If it's say a quarter of the hollow section being removed & you know the centroid of the quarter section of wall from the center, then all you need to work it out is to recognise you have 4 quarters and it's simple maths from then on and a b8t of basic engineering theory.

 

[paddingtongreen]

Question: Are the cuts radial from the center or in line along the segment?

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin