Two Overhang Beam with UDL

Two Overhang Beam with UDL - Moment diagram Problem - Messages

#1 Posted: 2/20/2023 11:33:13 AM
yoswos

yoswos

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I have attached a mathcad file.. and the moment diagram at the end doesn't match
with expcted output.. it should have gone smoothly to end with x coordinate 5m.
but at certain point it has jumped to postive rigion.

Please help fix it.
Thanks

File not found.File not found.
#2 Posted: 2/20/2023 5:05:51 PM
overlord

overlord

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I have no idea why mathcad plots that segment faulty.
But it is possible to plot correct graphic in SMath.
However SMath integration is not very good and fast.
It will take much more time than mathcad, and zig-zagy.
You can improve plot by increasing Integrate: Accuracy.
It is in Tools>Options>Calculation.

Regards

PS: I increased accuracy to 500 to get a decent plot.
It took 50 seconds to plot in the picture!!
Integration should really be improved.

UDL.sm (18 KiB) downloaded 36 time(s).

2023-02-20_22-50.png
#3 Posted: 2/20/2023 6:14:20 PM
Martin Kraska

Martin Kraska

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In the interactive handbook you can find examples for beam analysis.

They use symbolic integration and equation solving with Maxima. This is very fast, except for the Maxima restart at the beginning of the sheet (can be removed if all works well).

Show Spoiler



example maxima beam.sm (41 KiB) downloaded 31 time(s).
Martin Kraska Pre-configured portable distribution of SMath Studio: https://en.smath.info/wiki/SMath%20with%20Plugins.ashx
#4 Posted: 2/21/2023 2:35:40 AM
yoswos

yoswos

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Sorry but I have problem again

with M(5m)=-0.2083 kN m
it should have been
M(5m)=0
#5 Posted: 2/21/2023 2:42:21 AM
yoswos

yoswos

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Wrote

Sorry but I have problem again

with M(5m)=-0.2083 kN m
it should have been
M(5m)=0




My sorry it is correct.. since it is overhang it should have moment at the end;;

#6 Posted: 2/21/2023 2:49:22 AM
overlord

overlord

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Though it should be smaller. Probably zero by the way.
Result can be reduced with integral accuracy set to 10000.
SMath integral algorithms are not good enough.

Regards

2023-02-21_08-45.png
#7 Posted: 2/21/2023 4:46:08 AM
Alvaro Diaz Falconi

Alvaro Diaz Falconi

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Hi. Remembering that solving an ODE is also told to integrate it:


UDL.sm (22 KiB) downloaded 31 time(s).

int.png

The domain can also be restricted to M(x) by multiplying it by the corresponding inequalities.

Best regards.
Alvaro.
2 users liked this post
Вячеслав Мезенцев 2/21/2023 7:54:00 AM, NDTM Amarasekera 2/21/2023 11:27:00 AM
#8 Posted: 2/21/2023 10:02:18 AM
Jean Giraud

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Wrote

My sorry it is correct.. since it is overhang it should have moment at the end;;


Finite Differences [FD] is a very good yardstick insensitive to noise.
It that what you mean moment at the end ?
Cheers ... Jean.

Page2 FD.sm (57 KiB) downloaded 18 time(s).
#9 Posted: 2/21/2023 11:29:30 AM
overlord

overlord

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Wrote

Hi. Remembering that solving an ODE is also told to integrate it:
The domain can also be restricted to M(x) by multiplying it by the corresponding inequalities.

Best regards.
Alvaro.


This is a marvelous solution.
I learned a new thing today.
Thanks Razonar.

Maybe I am wrong but I think formula should be like this.
Huge kN*m values appear if calculated as in the picture above.

Regards

2023-02-21_17-24.png
1 users liked this post
Alvaro Diaz Falconi 2/21/2023 2:49:00 PM
#10 Posted: 2/21/2023 12:55:20 PM
Jean Giraud

Jean Giraud

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ODE integrator(s) range from exact [rarely]
approx. 4 decimals ... to glorious freak !
64 bits Smath does not have 32 bits Matlab ODE.
Recently checked on my PC2 this damned bug.
Cheers ... Jean.

ODE 0 TEST [17].sm (45 KiB) downloaded 20 time(s).

Revisit from few months ago.
#11 Posted: 2/21/2023 2:51:56 PM
Alvaro Diaz Falconi

Alvaro Diaz Falconi

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Wrote

Maybe I am wrong but I think formula should be like this.
Huge kN*m values appear if calculated as in the picture above ...



Hi overlord. You're absolutely right. Thanks for catching that error. Only 3 orders of magnitude. Who could worry about that? The Mathcad block can also be used, although I don't know if this is the best way to deal with the units, using an intermediate function Mo.

int.png

UDL.sm (26 KiB) downloaded 34 time(s).

Best regards.
Alvaro.
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