topic Re: Adding global bow imperfection to 3D structures in AutoCAD Forum

Adding global bow imperfection to 3D structures

Anonymous — Fri, 29 Mar 2019 12:19:39 GMT

Hi,

For my master thesis, we are researching the impact of imperfections on certain steel structures. We usually draw the structure in AutoCAD before exporting it to a FEM-software to perform calculations.

One of the imperfections is a global bow imperfection, wich can't be modelled within the FEM-software. So we want to draw the imperfection in AutoCAD.

We want to align the 3D structure/block with a curve (red arc in picture), so the entire structure gets a basic curve and excentricity.

Is this possible with AutoCAD? Or should we use other software? (we have acces to most Autodesk software like Inventor through our university, but we have no experience using those)

Our last option is drawing the structure from scratch, but since we have a array of different lenghts and shapes, that would be really impractial

Thank you in advance for the advice.

Re: Adding global bow imperfection to 3D structures

dbroad — Fri, 29 Mar 2019 12:22:17 GMT

Depending on what kind of representation you want, I've done similar changes with 3dsMax, which works with surfaces. I believe Revit can also do this. You might need to use Dynamo though.

Re: Adding global bow imperfection to 3D structures

Anonymous — Fri, 29 Mar 2019 12:43:23 GMT

The structure should preferably remain a wireframe, and not be converted to a solid structure. That way we can still use it to import to our FEM-software..

So you don't think this is possible with AutoCAD?

Re: Adding global bow imperfection to 3D structures

leeminardi — Fri, 29 Mar 2019 14:59:39 GMT

You can use AutoCAD to to create the geometry to feed to your FEM model. You can use Excel to create the node points that you insert into AutoCAD

For example, assume you wanted to use a parabolic shape for the bow in the structure rather than an arc.

In the attached Excel file the user can specify the dz value (the height of a structural cell), the number of cells in height for the structure, and a value for the coefficient a for parabola equation. Excel calculates the nodes (it is assumed the structure will lie on the XZ plane where Y = 0). Adjust the value of the coefficient a until an acceptable deflection is achieved then copy and paste the content of cells G13:G21 into AutoCAD after giving the line command.

Here are the result for a = 0.005 (green) and a = 0.0001 (yellow).

Re: Adding global bow imperfection to 3D structures

Anonymous — Fri, 29 Mar 2019 17:02:36 GMT

Thank you for the detailed answer.

I hadn't thought of using excel and importing the points into AutoCAD that way. With this method we can make new deformed structures rather quickly and they should be precise enough for our calculations. Thank you very much for the insight and the usefull excell sheet.