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3D Direct Stiffness Analysis

3D Direct Stiffness Analysis

3D Direct Stiffness Analysis

I have recently created a 3d stiffness analysis worksheet in Mathcad (It includes member end releases, member rotations includes 3d manipulative graphics display which also shows moments and shears for selected members) and have been checking it with Staad pro output. The results from my mathcad worksheet are near identical, if not exactly the same as the Staad output (generally any differences are attributable to round off with respect to member properties - Staad appears to sometimes slightly differing results depending on what method is used to extract properties data). The SET SHEAR command must be invoked in Staad since my worksheet doesnt include shear deformations which are gen negligible.

I attach a copy if anyone wants to test it out.

RE: 3D Direct Stiffness Analysis

This takes some serious mathcad ability I applaud you.

RE: 3D Direct Stiffness Analysis

Thanks, it did take some doing.

I also have a worksheet that calculates all the roark ring cases, which can be easily combined (i have also programed it in visual basic which also includes pages for calculating ring section properties and can combine several cases and produce a visual plot of moments, shears and von-mises stress, if you'd like to review them too.

RE: 3D Direct Stiffness Analysis

I would definitely like to take a look at your VB sheets if you're willing to share! VBA via Excel or otherwise?

RE: 3D Direct Stiffness Analysis

I take it you mean the code.

RE: 3D Direct Stiffness Analysis

Can you down-save your file to make it accessible to more users?

Your file is saved at Mathcad Professional 14.1 format which is not backward compatible with any earlier MC version.
For a deeper perspective from the users' point of view on various versions of MC, please feel welcome to read older posts on this sub-forum. It is discussed often, because the difficulties have existed for a very long time, and unlikely to improve.

A common coping mechanism is to down-save any file you intend to share with the membership to the lowest level that still permits your intended functionality.

I am keen to compare your 3D frame with my 2D frame worksheet.

RE: 3D Direct Stiffness Analysis


No problem. I completely forgot that I should maybe save it in an earlier version format.

Since I cannot check the compatibility with earlier versions myself, I'll save it as earlier formats and see what the responses are.

RE: 3D Direct Stiffness Analysis


Here is another ring program. it was a free download from a website that no longer exists. I remember at the time nearly 20 years ago trying to contact the company (lanxum.com) via their email address/tel number found under the help menu, but they were unresponsive or contactable on the tel number, although the website was still active for a year or two after, it is now no longer active, so I assume they have ceased trading.

I used the program as a way of verifying my VB program and is quite clever. Although it is only for flanges onto rings and only includes Roark cases 8, 20 and 19(MOM), it can takes account of flange load spread either to the edge of the ring or to the ring section n/a. Given how old it is I would suspect its written in Fortran. My VB program was developed from one I initially wrote in FORTRAN IV, which only used data file inputs/outputs since it was before the common use of VB, C, C++ etc (yup, that's how old I am....lol).

Note, the Help Menu will not work under windows 10, although it still should, if you are still using windows 7

RE: 3D Direct Stiffness Analysis

Hi Noratetoobig,
I completely underestimated what was coming. So in the 5 minutes I have right now, all I can do is scan the file, say "wow, thank you again for sharing" and promise to get back later when I can process this properly!

RE: 3D Direct Stiffness Analysis


Thanks for the wow. I must admit I am quite chuffed that I managed to make it quite detailed and as simple as I could for checking using the 3D graphics, which is one of the biggest problems associated with making structural packages.

Note. You need to go through it in detail since there are many things the graphics can show, such as. Section the structure which creates selectable lists of only the visible members. Display the displaced structure separately or with the original frame, clearly show which members have end releases/rotation's/and loaded member which, when selected, lists all loads associated with that member or joint as well as clearly show all members associated with a section property and highlight a selected member. I also included a (scalable) local axis system which shows up for a selected member giving its direction and rotation, if applicable. This too can be switched to show the section profile shape or just the local axis. The selected member force diagram (2D plot) can be selected to show shear/moment/deflection, which are also shown on a 3D plot. The 2D plot also indicates any section chosen by the user along the selected member using a slider and indicates the forces and deflections at that point (in either the selected local member y or z axes), as well as having a coloured 3D sectional plot (section shape is dependent on section of member) with colour intensity scaled gradually between max compression and max tensile stresses with accompanying tabulated 4 corner stresses, numbered as per staad, at the selected section.

Anyway, let me know if you find any issues. I think I have solved most, which were generally with the 3D graphical selection process.

RE: 3D Direct Stiffness Analysis

Can I ask you to check your MC13 version please?
Try opening the file you down-saved; even if you are using MC15, it should open. Check the values, check the locked sections, re-lock the locks, and save it again, as MC13. I'm not sure the conversion is not complete until you actually access the file and verify all of the calculations.

Other observations as I make them:
It starts off with a scripting warning. A lot like Excel does when there's a macro. No problem when I proceed.

My graphics card has the occasional moment. I've never seen Mathcad do that, but it's a thing I see doing CAD at times, so not a surprise as you've got a lot of 3d graphics going on.

Can you summarize the color coding? I'm not sure it's consistently used, because I need to edit some green fields (save path) and yellow fields (geometry). There are other green fields that are meant as instructions "See end of the worksheet..." and yellow fields with revisions listed, neither seem to be user-fields.

I'm not seeing an output file when I click "Write Data" on page 12.

Hard page breaks are preferable if you can't guarantee that every user will have the same paper size, margin size, etc.

Users should be told that the sheet extends to the right by 3 pages. I'm really not sure why Mathsoft allowed stuff to sprawl outside the right border but it is what it is by now. I find it randomly used, usually for scratch notes. Your work doesn't seem to be scratch on the right side. If ignored by some users they would miss important instructions.

You do building structures, so I'm not accustomed to your acronyms. Which section properties acronym refers to "HSS" structural rectangular tubing?

I figure as I continue to read through it, I might find the reason, but on page 3 I'm wondering why restraints aren't "fixed/pinned/free".

On page 4, should I see a value appear after FxTot after I hit [ctrl]-F9?
After page 5, most of the expressions show "undefined" errors.

On page 5, I suspect something may have been lost in translation to Mathcad R13. I'm seeing a plain grey box in the plot. It's probably the 3D graphic space as you defined it, but it's not getting the data to plot points. I don't use that type of plot very often - where do I find the arguments that generate the point data that is plotted?

I suppose if something is preventing FTot from gaining a value, there will be nothing to plot, so I have to figure out why that is broken, first. Do the default values (as opened for the very first time) give a valid result on your copy? Is this worksheet intended to be used by scrolling to the bottom first?

RE: 3D Direct Stiffness Analysis


Hi Sparweb,

Thanks for the feedback which I will go through and check and get back to you. I do actually have an old copy of MathCAD 13 which I'll install and see if I get the same issues.

Some of the information on the next 3 pages to the right are part of the StaadPro results I used for verification, however. There are some instances where formula are placed in the 2nd column to the right which are used as seeds to drop down menus. They are placed there so they can be excluded from a print dump of the main pages of the worksheet as there are already enough collapsed areas and adding one would make the printed page look more of a mess.

Its not necessary to scroll down the the bottom of the worksheet before using and in fact could cause scripting errors since list boxes are dependent on the info before which will need to be selected or input, this also applies to the plot areas. Initially I used comboboxes, however. I found that when saving, comboboxes are reset causing scripting errors and sometimes they ceased to function, which is due them being a separate MS script. As such, I changed them all to MathCADs own textboxes and have them auto select a value at start-up, however. They should all be blue indicating a selection has been made. If not, then make a selection before moving down.

As far as I am aware there isn't an HSS section, however. To the right of the Properties input is a list of what sections are used.
I tend to use a desktop so see 3 column widths, but obviously if a user only has a laptop, I can understand the concern, I can add a note at the top so users are aware that some calculations and notes can be in the second column.

Anyway, I'll get back to you about the rest once I've had a proper look using MC13.

Please see the attached which you may find of interest/use.

RE: 3D Direct Stiffness Analysis

Thanks for sharing that item. I'll take a look; it does look interesting. Is it meant for anyone else's eyes? If not, for a limited time after you post on this forum, you are able to edit and/or delete parts of your posts. Just a thought, just in case.

RE: 3D Direct Stiffness Analysis

Well, that explains why I couldn't find the target on the first one. :)

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