## NX 11.0: Wrong beam deflection results

## NX 11.0: Wrong beam deflection results

(OP)

Hi,

I am doing a simple problem of a beam fixed at both ends and carrying a uniform distribiuted load, material is steel. The results given by NX are different from the results I get using beam deflection formulas (Theoretical).

In attachments I have attached the beam problem, Beam theory formulas used to calculate deflection and results given by NX.

Since the Moment of Inertia, Modulus of Elasticity values are taken as given by NX itself, and also values of load and beam dimensions are displayed by NX itself , it does not make much sense why both the results are different.

Deflection (Y) given by beam theory is : 1.350E-5 mm and by NX is 2.286E-5 mm which is an error of 69 %.

Whereas the results for Bending stress is coming exactly same from both theory formulas and NX. Can anybody explain why am I getting theses kind of results.

Thanks,

Ashwani Thakur.

I am doing a simple problem of a beam fixed at both ends and carrying a uniform distribiuted load, material is steel. The results given by NX are different from the results I get using beam deflection formulas (Theoretical).

In attachments I have attached the beam problem, Beam theory formulas used to calculate deflection and results given by NX.

Since the Moment of Inertia, Modulus of Elasticity values are taken as given by NX itself, and also values of load and beam dimensions are displayed by NX itself , it does not make much sense why both the results are different.

Deflection (Y) given by beam theory is : 1.350E-5 mm and by NX is 2.286E-5 mm which is an error of 69 %.

Whereas the results for Bending stress is coming exactly same from both theory formulas and NX. Can anybody explain why am I getting theses kind of results.

Thanks,

Ashwani Thakur.

## RE: NX 11.0: Wrong beam deflection results

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Irvine, CA

Siemens PLM:

UG/NX Museum:

The secret of life is not finding someone to live withIt's finding someone you can't live without

## RE: NX 11.0: Wrong beam deflection results

another day in paradise, or is paradise one day closer ?

## RE: NX 11.0: Wrong beam deflection results

Regards,

Joe

## RE: NX 11.0: Wrong beam deflection results

@ rb1957, counln't get what you are saying, please elaborate.

Thanks All

## RE: NX 11.0: Wrong beam deflection results

I think the problem is shear deflections ... your web is quite large (3m long, 1/3rd m high) ... shear deflections need to be added to the flexural deflections you're using)

another day in paradise, or is paradise one day closer ?

## RE: NX 11.0: Wrong beam deflection results

I'd've thought that the 1D beam element should match the beam theory.

another day in paradise, or is paradise one day closer ?

## RE: NX 11.0: Wrong beam deflection results

Thanks.

## RE: NX 11.0: Wrong beam deflection results

else calc the deflection due to shear

another day in paradise, or is paradise one day closer ?

## RE: NX 11.0: Wrong beam deflection results

NX has written the following PBEAML property:

$* Property: PBEAML1

$* Section: I(1)

PBEAML 1 3 MSCBML0 I +

+ 340.0000250.0000250.0000 20.0000 20.0000 20.0000 0.0000 YES+

+ 1.000000340.0000250.0000250.0000 20.0000 20.0000 20.0000 0.0000

If you use "echo=punch" then you will see Nastran converts that to the following PBEAM:

PBEAM * 1 3 1.60000000E+04 3.01333333E+08

* 5.22833333E+07 0.00000000E+00 2.18666667E+06 0.00000000E+00

* 1.70000000E+02 1.25000000E+02 -1.70000000E+02 1.25000000E+02

* -1.70000000E+02 -1.25000000E+02 1.70000000E+02 -1.25000000E+02

* 3.75000000E-01 5.20833333E-01 0.00000000E+00 0.00000000E+00

* 0.00000000E+00 0.00000000E+00 1.33333333E+12 1.33333333E+12

* 0.00000000E+00 0.00000000E+00 0.00000000E+00 0.00000000E+00

* 0.00000000E+00 0.00000000E+00 0.00000000E+00 0.00000000E+00

If you set the shear factors(* 3.75000000E-01 5.20833333E-01) to zero and use that property entry, which will look like this:

PBEAM * 2 3 1.60000000E+04 3.01333333E+08

* 5.22833333E+07 0.00000000E+00 2.18666667E+06 0.00000000E+00

* 1.70000000E+02 1.25000000E+02 -1.70000000E+02 1.25000000E+02

* -1.70000000E+02 -1.25000000E+02 1.70000000E+02 -1.25000000E+02

* 0.00000000E+00 0.00000000E+00 0.00000000E+00 0.00000000E+00

* 0.00000000E+00 0.00000000E+00 1.33333333E+12 1.33333333E+12

* 0.00000000E+00 0.00000000E+00 0.00000000E+00 0.00000000E+00

* 0.00000000E+00 0.00000000E+00 0.00000000E+00 0.00000000E+00

I have attached the modified dat file for you to try. Also the note below is from the PBEAM documentation in the QRG, note 13:

13. The shear stiffness factors K1 andK2 adjust the effective transverse shear

cross-section area according to the Timoshenko beam theory. Their default

values of 1.0 approximate the effects of shear deformation. To neglect shear

deformation (i.e., to obtain the Bernoulli-Euler beam theory), the values of K1

and K2 should be set to 0.0.

Regards,

Joe

## RE: NX 11.0: Wrong beam deflection results

2) can you see them if using NX thru FeMap ? (maybe we've found a FeMap angle ?)

3) If you zero the shear area (in the FeMap property input) does that zero these factors ?

another day in paradise, or is paradise one day closer ?

## RE: NX 11.0: Wrong beam deflection results

Thanks,

Ashwani Thakur.