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Distinguished Contributor
scudelari
Posts: 109
Registered: ‎10-11-2011

Von Mises BEAM STRESS

994 Views, 8 Replies
11-03-2012 07:21 AM

Hello Everyone,

 

What is the reason why Simulation does not calculate the Von Mises stress of beams?

 

Is it wrong from the physical point of view to make analysis of beams using such stress?

 

Because Simulation does have a result that is the "Worst" stress.

 

Basically what I want to to do is to compare the stress (either the Von Mises of the "Worst") on the beam and compare with the allowable value given by the material definiton. Is this correct to do?

 

Thanks a lot!

 

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Distinguished Contributor
madg1
Posts: 108
Registered: ‎03-16-2012

Re: Von Mises BEAM STRESS

11-05-2012 05:21 AM in reply to: scudelari

if you want von mises stress, you need to use 3d elements.so make a 3d model and mesh it with solid elements.

if you use beam elements (2d or 3d),you get stresses(no von mises),strains,displacements only at nodes.

if you need more sophisticated answer, you can wait for more replies.

 

madg1
ASIMM 2012
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Distinguished Contributor
scudelari
Posts: 109
Registered: ‎10-11-2011

Re: Von Mises BEAM STRESS

11-05-2012 05:46 AM in reply to: madg1

Hello madg1,

 

I appreciate the answer, but that does not answer so much my question. 

 

I wanted the know simply what is the reason for not having Von Mises stress. 

 

Basically, why are they not shown in the vertices of the beams? Specially if you have one beam whose lines are split into several (so you can see the progression of stress on the beam.

 

Thanks!

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Valued Mentor
AstroJohnPE
Posts: 501
Registered: ‎08-30-2012

Re: Von Mises BEAM STRESS

11-05-2012 08:14 AM in reply to: scudelari

Hi,

 

My thought is that Simulation Mechanical does not calculate any shear stress in the beams (nor torsion). So without those results, the von Mises stress would be inaccurate.

 

John Holtz, PE
Mechanical Engineer
Pittsburgh, PA

16 years experience with Simulation Mechanical
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Distinguished Contributor
scudelari
Posts: 109
Registered: ‎10-11-2011

Re: Von Mises BEAM STRESS

11-05-2012 08:43 AM in reply to: AstroJohnPE

Hi AstroJohn,

 

Indeed it does not. But it does also calculate the following properties:

11-5-2012 2-39-11 PM.png

 

With the Section Modulus, it should be possible to calculate the Shear Stresses on the beams, right?

 

It should be ShearStress = ShearForce / Moment of Inertia

 

Why doesn't simulation calculate this?

 

I am asking because,l well, if it does not calculate if could be wrong to assume the abovementioned equation....

 

Thansk for the intel!

 

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Active Member
rlkillian
Posts: 9
Registered: ‎09-05-2012

Re: Von Mises BEAM STRESS

11-05-2012 11:44 AM in reply to: scudelari

Shear stress is NOT shear force/ moment of inertia. It is VQ/Ib.  I'll leave it to you to look up what that means. Some references may use t instead of b.

 

In addition, even though Simulate does indeed have beam elements. Designing beams usually in done in programs such as STAAD.Pro, RISA 3D, or SAP 2000. In other words, something specifically meant to find the forces and moments in beams then apply the AISC code to determine if theyare OK.  Not to be unkind, but it sounds like you're out of your depth on this.

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Distinguished Contributor
madg1
Posts: 108
Registered: ‎03-16-2012

Re: Von Mises BEAM STRESS

11-05-2012 11:45 AM in reply to: rlkillian

we can use asim for aisc code check.

madg1
ASIMM 2012
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Distinguished Contributor
scudelari
Posts: 109
Registered: ‎10-11-2011

Re: Von Mises BEAM STRESS

11-05-2012 12:12 PM in reply to: rlkillian

True. My mistake. Your answer was quite arrogant as well and I did not appreciate the unpoliteness.

 

It is not because you say "not to be unkind" that you cease to be unkind. I am not a master of this - WHICH GIVES MORE REASON TO ASK THE QUESTION.

 

Regardless of that, the shear formula has everything constant for the beam except the first moment Q; The highest value - worst case - of Q is on the neutral axis; therefore the "worst shear stress" could be calculated.

 

By the way, saying that:


In addition, even though Simulate does indeed have beam elements. Designing beams usually in done in programs such as STAAD.Pro, RISA 3D, or SAP 2000. 


Is entirely useless to the discussion, which was - may I recall - what is the reason why Simulation does not calculate the Von Mises stress of beams?

 

Sincerely,

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New Member
vvk.pentapati
Posts: 1
Registered: ‎07-30-2014

Re: Von Mises BEAM STRESS

07-30-2014 11:32 PM in reply to: scudelari

Vonmisses Index is used when a region is subjected to various stresses. It could be combination of a shear and normal stresses or only normal stress. 

 

Coming to the point, in a beam shear stress distribution starts from zero on top fibre and reaches maximum at the centre of the cross section. But Bending stress is maximum in the top fibre or bottom fibre (could be compression or tension) and zero in the centre of the cross section. While considering a maximum we have case of Max normal stress on the top without shear and other case of shear stress at the centre without tension. 

 

So there is no necessity of calculating vonmisses in beams.

 

Hope this helps, although late reply.

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