Shear Stress in CBAR element under end in-plane torque load

[bcosm13]

Hi all,

I am new to MSC.Nastran/Patran. I have modeled a beam along Z-Direction (one end is fixed and other end is free) with CBAR elements. The cross section of the beam is box-shaped. The free end is loaded with torque load(Mz - XY Plane). The problem is I am not able to get any stress results from. I also tried CBEAM but still I get no results.

Both CBAR and CBEAM have torsional (transverse shear) stiffness but they give no response in stress-wise. Is there any parameter or keyword to invoke shear stiffness? Do you have any tips about this?

http://www.aero.polimi.it/~lanz/bacheca/downloads/cost/aa10_11/MD_Nastran_Elements_2.pdf

Thanks in advance,

(This is the .bdf file)

$ Direct Text Input for Nastran System Cell Section
$ Direct Text Input for File Management Section
$ Direct Text Input for Executive Control
$ Linear Static Analysis, Database
SOL 101
CEND
$ Direct Text Input for Global Case Control Data
TITLE = MSC.Nastran job created on 10-Aug-14 at 13:11:15
ECHO = NONE
SUBCASE 1
   SUBTITLE=beamonlycase
   SPC = 2
   LOAD = 2
   DISPLACEMENT(SORT1,REAL)=ALL
   SPCFORCES(SORT1,REAL)=ALL
   GPFORCE=ALL
   STRESS(SORT1,REAL,MAXS,BILIN)=ALL
$ Direct Text Input for this Subcase
BEGIN BULK
$ Direct Text Input for Bulk Data
PARAM    POST    0
PARAM   PRTMAXIM YES
$ Elements and Element Properties for region : realbeam
PBARL    1       1               BOX
        500.    300.    2.      2.
$ Pset: "realbeam" will be imported as: "pbarl.1"
CBAR     1       1       1       3       0.     1.       0.
CBAR     2       1       3       4       0.     1.       0.
CBAR     3       1       4       5       0.     1.       0.
CBAR     4       1       5       6       0.     1.       0.
CBAR     5       1       6       7       0.     1.       0.
CBAR     6       1       7       8       0.     1.       0.
CBAR     7       1       8       9       0.     1.       0.
CBAR     8       1       9       10      0.     1.       0.
CBAR     9       1       10      11      0.     1.       0.
CBAR     10      1       11      12      0.     1.       0.
CBAR     11      1       12      13      0.     1.       0.
CBAR     12      1       13      14      0.     1.       0.
CBAR     13      1       14      15      0.     1.       0.
CBAR     14      1       15      16      0.     1.       0.
CBAR     15      1       16      17      0.     1.       0.
CBAR     16      1       17      18      0.     1.       0.
CBAR     17      1       18      19      0.     1.       0.
CBAR     18      1       19      20      0.     1.       0.
CBAR     19      1       20      21      0.     1.       0.
CBAR     20      1       21      22      0.     1.       0.
CBAR     21      1       22      23      0.     1.       0.
CBAR     22      1       23      24      0.     1.       0.
CBAR     23      1       24      25      0.     1.       0.
CBAR     24      1       25      26      0.     1.       0.
CBAR     25      1       26      27      0.     1.       0.
CBAR     26      1       27      28      0.     1.       0.
CBAR     27      1       28      29      0.     1.       0.
CBAR     28      1       29      30      0.     1.       0.
CBAR     29      1       30      31      0.     1.       0.
CBAR     30      1       31      32      0.     1.       0.
CBAR     31      1       32      33      0.     1.       0.
CBAR     32      1       33      34      0.     1.       0.
CBAR     33      1       34      35      0.     1.       0.
CBAR     34      1       35      36      0.     1.       0.
CBAR     35      1       36      2       0.     1.       0.
$ Referenced Material Records
$ Material Record : steel
$ Description of Material : Date: 10-Aug-14           Time: 13:02:58
MAT1     1      7.86-9          .3
$ Nodes of the Entire Model
GRID     1               0.      0.      0.
GRID     2               0.      0.     3500.
GRID     3               0.      0.     100.
GRID     4               0.      0.     200.
GRID     5               0.      0.     300.
GRID     6               0.      0.     400.
GRID     7               0.      0.     500.
GRID     8               0.      0.     600.
GRID     9               0.      0.     700.
GRID     10              0.      0.     800.
GRID     11              0.      0.     900.
GRID     12              0.      0.     1000.
GRID     13              0.      0.     1100.
GRID     14              0.      0.     1200.
GRID     15              0.      0.     1300.
GRID     16              0.      0.     1400.
GRID     17              0.      0.     1500.
GRID     18              0.      0.     1600.
GRID     19              0.      0.     1700.
GRID     20              0.      0.     1800.
GRID     21              0.      0.     1900.
GRID     22              0.      0.     2000.
GRID     23              0.      0.     2100.
GRID     24              0.      0.     2200.
GRID     25              0.      0.     2300.
GRID     26              0.      0.     2400.
GRID     27              0.      0.     2500.
GRID     28              0.      0.     2600.
GRID     29              0.      0.     2700.
GRID     30              0.      0.     2800.
GRID     31              0.      0.     2900.
GRID     32              0.      0.     3000.
GRID     33              0.      0.     3100.
GRID     34              0.      0.     3200.
GRID     35              0.      0.     3300.
GRID     36              0.      0.     3400.
$ Loads for Load Case : beamonlycase
SPCADD   2       1
LOAD     2      1.      1.       1      1.       3
$ Displacement Constraints of Load Set : fixed
SPC1     1       123456  1
$ Nodal Forces of Load Set : load
FORCE    1       2       0       0.     .57735  .57735  .57735
$ Nodal Forces of Load Set : load
MOMENT   3       2       0      100.     0.      0.     -1.
$ Referenced Coordinate Frames
ENDDATA 5319d802

 

[BlasMolero]

Hello!,
In fact, nastran do not compute at all neither shear or torsional stresses for cbar/cbeam elements, but not only nastran, in general any FEA codes of type "general purpose" do not compute shear/torsional stresses in bar/beam elements because the assumption for beam elements follows the beam theory where torsion and shear stresses are negligible in comparison with axial + bending combination stresses. If this is not true, then you should use other elements like plane & shell elements or solid elements (by the way, I read your model in FEMAP and it is not appropiate at all to use a CBAR element to represent a hole box cross section of 500x300 with very LOW thickness = 2.0!!. Not correct, if this is a real situation you must use plate CQUAD4 elements and run a nonlinear analysis to account for geometric nonlinear behaviour).

But fortunately for the FEMAP users we have THE BEAM CALCULATOR utility under the FEMAP postprocessor tools that is able to consider not only axial & bending forces in bar/beam elements but also shear & torsion forces coming from any FEA solver (nastran, ansys, abaqus, etc..) to compute not only vonMises stress but also axial, shear and principal stresses along the beam elements. To learn more take a look to this link:

http://iberisa.files.wordpress.com/2014/06/12_beamcalculator_kriengsiri_splm.pdf

Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48004 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

http://iberisa.wordpress.com/

 

[bcosm13]

@BlasMolero: Thanks for the good reply. Actually, that beam is a symbolic one for my benchmark. I faced with this problem when I was working on 3D to stick model connection.
What I remeber from Ansys is, BEAM 188 element is capable to reflect shear stresses without any additional implementations. After your advise, I am gonna focus on FEMAP more deeply.