Calculation of plastic modulus

[jamami]

I regularly have to calculate the plastic modulus and plastic neutral axis of complex cross sections.

To do this I have to locate the centre of area ie axis that divide the shape into equal areas either side.

For symmetrical shapes this is obvious, but for complex shapes like T, L, V and custom extrusions it is not obvious at all. Some shapes like T,L etc can be hand calculated quite easily and the axis then positioned to suit. Some extrusions are really complex and do not lend themselves to hand calculation. For these I draw an axis, create a region above and below look at the values and then keep moving the axis and repeating until the 2 values are equal (or thereabouts)-this is really crude and takes ages.

 

I have often thought it would be great if the divide command would be able to divide the areas, but to do this it would need to know the orientation of the axis each side of which the area must be equally distributed.

 

A contact suggested use of iLogic to do this, but I do not know this software. I would welcome thoughts from this forum on how this could be acheived using customisations.

[Organic]

From memory, if you have STAAD, that can import a dxf section and give you all the section properties for it.

[LibertyOne]

AutoCAD Mechanical has this built in to it.

[Manila Wolf]

This may be of help. There is a lisp that calculates the elastic modulus. It can be found here: -

 

http://www.cadstudio.cz/download

 

Modulus - section modulus (Wx/Wy) for 2D profiles (VLX Lisp for AutoCAD)

 

I use it in conjunction with the AutoCAD mass properties command.

Edited March 21, 2017 by Manila Wolf
In the first line I wrote plastic modulus. Should have been elastic modulus.

[jamami]

This may be of help. There is a lisp that calculates the plastic modulus. It can be found here: -

 

http://www.cadstudio.cz/download

 

Modulus - section modulus (Wx/Wy) for 2D profiles (VLX Lisp for AutoCAD)

 

I use it in conjunction with the AutoCAD mass properties command.

 

 

 

Thanks for the link, I will try and find that routine in the library.

[ossbbg]

I got tired of doing these calculations by hand too. I recently found a plugin-in for google SketchUp that will calculate the plastic neutral axis and plastic section modulus. Here is the link to the website. http://www.skpengineering.com. The plug-in is called section properties calculator.

[jamami]

I got tired of doing these calculations by hand too. I recently found a plugin-in for google SketchUp that will calculate the plastic neutral axis and plastic section modulus. Here is the link to the website. http://www.skpengineering.com. The plug-in is called section properties calculator.

 

Thanks for the tip. I am surprised to see such a technical app for sketchup, I thought this was a 'toy'. Obviously not the case. Do you know how accurate this routine is? hav you calibrated it against known results?

[ossbbg]

Thanks for the tip. I am surprised to see such a technical app for sketchup, I thought this was a 'toy'. Obviously not the case. Do you know how accurate this routine is? hav you calibrated it against known results?

 

 

I was a bit reluctant to download the plug-in at first because I thought SketchUp was mostly used for architectural applications, but it turns out that the output is quite accurate. I checked my SketchUp results with a few spreadsheets I wrote to calculate the plastic modulus and the results checked out; I also double checked the location of the plastic neutral axis(PNA) by drawing a line that split the shape above and below the PNA and found that the areas above and below the PNA varied by about 1/1000 of an inch squared, so looks like it does a fairly good job of locating the PNA.

[bonsoschmidt]

Hi, in my search for a structural engineering addition for sketchup, I came across your post in that blog regarding the skpengineering plugin.

Unfortunately the WWW has vanished. I would really like to test the plugin. You still have it somwhere on your computer?

 

Thank you in extend

[jamami]

Sorry, I do not have this anymore.

[jac1]

On 3/13/2015 at 4:31 PM, bonsoschmidt said:

Hi, in my search for a structural engineering addition for sketchup, I came across your post in that blog regarding the skpengineering plugin.

Unfortunately the WWW has vanished. I would really like to test the plugin. You still have it somwhere on your computer?

 

Thank you in extend

here: https://sketchucation.com/pluginstore?listtype=2&author=1132&category=0

 

also this one: https://github.com/alexschreyer/Face-Centroid-and-Properties-Plugin