# Obtaining the section modulus.( for a beginner)

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The Moment of Inertia provided by the massprop command is relative to the ACTIVE UCS (world or user).  The Principal moment is relative to the centroid.  The difference between your result  for moment of inertia and other calculations may be due to the location of the region relative to 0,0,0 in the drawing file.

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ok, so i will explain using units. Statical moment of inertia( or other words first moment of inertia or section of modulus) has units mm^3 or cm^3. Second moment of inertia has mm^4 or cm^4.  we are not able to obtain section of mouduls by MASSPROP comand.

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Paulina,

Are you looking for elastic section modulus?

If so, Tharwat has expertly addressed this in the previous thread that you provided a link to.

Something like in this attached drawing maybe?

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Do you mean "Second Moment of Area" a.k.a. area moment of inertia, or second area moment?

I think MASSPROP will do that, it needs to be a Region AFAIK. If it's hollow SUBTRACT one region from another. The Centroid needs to be at 0,0. You find the Centroid with MASSPROP, move the shape to Centroid at 0,0 run MASSPROP again and Ix and Iy should be what you need.

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Thank you @Manila Wolf for your nice words.

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14 hours ago, Tharwat said:

Thank you @Manila Wolf for your nice words.  ﻿

You're very welcome Tharwat. Credit where it's due.

Edited by Manila Wolf

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On 3/15/2019 at 3:52 AM, paulina.styrczula said:

ok, so i will explain using units. Statical moment of inertia( or other words first moment of inertia or section of modulus) has units mm^3 or cm^3. Second moment of inertia has mm^4 or cm^4.  we are not able to obtain section of mouduls by MASSPROP comand.

You are correct in that the MASSPROP command will not display section modulus.
MASSPROP will give you the two elements you need to calculate the section modulus. Those two elements being the Moments of Inertia and the bounding box dimensions.
Section modulus units are indeed mm^3 or cm^3.

See the screenshot taken from the dwg I uploaded previously.

To enable such a listing of these section properties, a block that has particular attributes, has to be inserted in the drawing. (Exploded if necessary).
The shape you have drawn is a region with the hollows correctly subtracted. That is good.
When running the lisp routine select the region first and then immediately select the block.

If you need a block and the lisp written by Tharwat (slightly modified by me but still credited to Tharwat of course), I can upload them here.
The question would be what units would you be expecting?
I assume your shape is drawn in mm. Do you need the resultant section modulus in mm^3 or cm^3.

Do you need the weight as part of the listing also? in kg/m?
If you do, the density of the concrete is required. It may be something like 2.32 g/cm^3

Alternative: -

If you just need the section modulus only, maybe this will suffice. See the link: -

This is a protected lisp. With extension .vlx
Not everybody is happy to activate such a routine without knowing what's inside it.
I have used it for many years without any problems. (Just saying).

Hope this post helps.

Edited by Manila Wolf

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