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justhumm10-Marble
10-Marble
December 29, 2023
Solved

Simple beam analysis - moment equation...?

  • December 29, 2023
  • 2 replies
  • 3016 views

I was looking at the sample worksheet (PDF) posted on the PTC website and I created a (supposed to be) matching MathCAD Prime 7.0 worksheet.

 

https://community.ptc.com/t5/Mathcad/Building-Structural-Design-Single-Span-Beams-Shear-and-Moment/td-p/450598 

 

Almost everything matches the sample PDF results...the Shear values, shear graph, and maximum Moment.

 

BUT the moment function and graph points are way off.

 

I've skimmed over everything multiple times and I can't see any typos or errors.

Can anyone see where the error is? Thanks!

Best answer by Werner_E

Again vectorization does the job

Werner_E_0-1703890609491.png

And again my question - why bother with the vectors when you simply want a plot of a function to be done? (Thats what Excel people have to do but its not necessary to do so in Mathcad or Prime).

Werner_E_1-1703890725798.png

 

You may also use Primes Quickplot feature which means that you don't have to define the variable (xm) for the abscissa at all (neither as a vector, nor as a range). You have to edit the axis ticks (first, second and last) to get the plot done for the desired range from 0 to 27. Prime will automatically use appropriate values for xxm even though its not defined. But Prime will only use simple scalars. So if you need unit, you will have to multiply xxm by the desired unit and that doesn't look really good.

Werner_E_0-1703957768141.png

I find that its easier and gives better control to define a range variable like xm to be used in the plot.

 

2 replies

W
Werner_E25-Diamond IAnswer
25-Diamond I
December 29, 2023

Again vectorization does the job

Werner_E_0-1703890609491.png

And again my question - why bother with the vectors when you simply want a plot of a function to be done? (Thats what Excel people have to do but its not necessary to do so in Mathcad or Prime).

Werner_E_1-1703890725798.png

 

You may also use Primes Quickplot feature which means that you don't have to define the variable (xm) for the abscissa at all (neither as a vector, nor as a range). You have to edit the axis ticks (first, second and last) to get the plot done for the desired range from 0 to 27. Prime will automatically use appropriate values for xxm even though its not defined. But Prime will only use simple scalars. So if you need unit, you will have to multiply xxm by the desired unit and that doesn't look really good.

Werner_E_0-1703957768141.png

I find that its easier and gives better control to define a range variable like xm to be used in the plot.

 

    J
    justhumm10-MarbleAuthor
    10-Marble
    January 3, 2024

    I tried putting the Shear and Moment calculations into standalone functions.

    Similarly to what I was running into before, the shear calculation is correct (once someone pointed out my stupid mistakes), but the moment calculation is "incorrect" similar to 

    I tried vectorizing the result and a few other locations. It either had no effect or it returned an error message that "the vectors must be the same size".

    Can anyone see where the error is? Thanks!

     

    error3.png

    L
    LucMeekes23-Emerald IV
    23-Emerald IV
    January 3, 2024

    The error occurs because a and w are 3-element vectors, while p is a 2-elememnt vector. For vectorisation, all vectors need to be the same size (length). The other parameters to the function are scalars, that's OK.

     

    Success!
    Luc

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