REF Node of Pretension Section . Reaction Force

Analysis issues
1

Hi,

Any idea why RF on the pretension section reference node do not deliver the expected value?

Pretension load 1000 N.

Section print of the pretension section 9.999600E+02 N

RF at the BC : 1000 N .

RF at Pretension section reference node (37) : 6.250000E+01 N (Unexpected ¿?¿)

Thanks.

*NODE
1,0,0,0
2,0.001,0,0
3,0.001,0.001,0
4,0,0.001,0
5,0,0,0.001
6,0.001,0,0.001
7,0.001,0.001,0.001
8,0,0.001,0.001
9,0.0005,0,0
10,0.001,0.0005,0
11,0.0005,0.001,0
12,0,0.0005,0
13,0.0005,0,0.001
14,0.001,0.0005,0.001
15,0.0005,0.001,0.001
16,0,0.0005,0.001
17,0,0,0.0005
18,0.001,0,0.0005
19,0.001,0.001,0.0005
20,0,0.001,0.0005
21,0.0005,0,0.0005
22,0.001,0.0005,0.0005
23,0.0005,0.001,0.0005
24,0,0.0005,0.0005
25,0.0005,0.0005,0
26,0.0005,0.0005,0.001
27,0.0005,0.0005,0.0005
28,0.000475,0.0005,0
29,0.000475,0.001,0
30,0.000475,0.001,0.0005
31,0.000475,0.0005,0.0005
32,0.000475,0.001,0.001
33,0.000475,0.0005,0.001
34,0.000475,0,0
35,0.000475,0,0.0005
36,0.000475,0,0.001
37,0,0,0
*ELEMENT,TYPE=C3D8I
1,24,31,30,20,16,33,32,8
2,1,34,28,12,17,35,31,24
3,9,2,10,25,21,18,22,27
4,25,10,3,11,27,22,19,23
5,12,28,29,4,24,31,30,20
6,17,35,31,24,5,36,33,16
7,21,18,22,27,13,6,14,26
8,27,22,19,23,26,14,7,15
9,25,27,23,11,28,31,30,29
10,27,26,15,23,31,33,32,30
11,9,21,27,25,34,35,31,28
12,21,13,26,27,35,36,33,31
*ELSET,ELSET=DEFAULT
1
2
3
4
5
6
7
8
9
10
11
12
*SURFACE,NAME=REACTION
8,S4
4,S4
7,S4
3,S4
*SURFACE,NAME=PRETENSIONSECTION
9,S1
10,S1
11,S1
12,S1
*MATERIAL,NAME=MATERIAL
*ELASTIC,TYPE=ISOTROPIC
210000000000,0.3
*SOLID SECTION,ELSET=DEFAULT,MATERIAL=MATERIAL
*BOUNDARY
1,1,,0
2,1,,0
3,1,,0
3,3,,0
4,1,,0
4,3,,0
5,1,,0
6,1,,0
7,1,,0
8,1,,0
10,1,,0
10,2,,0
12,1,,0
12,2,,0
14,1,,0
14,2,,0
16,1,,0
16,2,,0
17,1,,0
18,1,,0
19,1,,0
20,1,,0
22,1,,0
24,1,,0
*AMPLITUDE,NAME=pretensionsection1
0,0
1,1000
*PRE-TENSION SECTION,SURFACE=PRETENSIONSECTION,NODE=37
1.000000000000E+000,0.000000000000E+000,0.000000000000E+000
*NSET,NSET=N_REACT
37
*STEP,NLGEOM=YES,INC=100,AMPLITUDE=STEP
*STATIC
0.1,1,0,0.1
*CLOAD,AMPLITUDE=pretensionsection1
37,1,1
*NODE FILE,GLOBAL=YES
U,RF
*EL FILE
S,NOE,E,ENER
*CONTACT FILE
CDIS,CSTR
*SECTION PRINT,SURFACE=PRETENSIONSECTION,NAME=Reaction_forces
SOF,SOM

*NODE PRINT,NSET=N_REACT,NAME=Reaction_Node
RF,U

*END STEP
2

sorry, forget my last post… still had an error in the deck. The deck itself seems ok, since ABAQUS yields correct output

   THE FOLLOWING TABLES ARE PRINTED

        SOFM        SOF1        SOF2        SOF3        SOMM        SOM1        SOM2        SOM3

         1000.       1000.     -1.5715E-14 -4.7307E-15  0.7066      4.6111E-18  0.4993     -0.5000
3

For a beam of completely different geometry (4mm x 2mm x 2mm) but still 1000N pre-tension I get the same result as above:

9.999600E+02 N (i.e. off by the tiny fraction of 4E-05N)

So I assume adding the float integration point weights and locations in the element up yields a very small error.

And yes, the reaction force for the pre-tension node does obviously NOT match the pre-tension force, in my example it is 1/8 of the applied load, in yours 1/16… we can check this

4

Hi @chewbacca ,

Thanks for looking at this.

Seem Rf on the ref node of a pretension section is not working properly. I will post on GitHub.

I agree Section print is right .

Thank you again.

5

Since 62.5N (corner), 125N (mid-side) and 250N (center) are the nodal reaction forces depending on the nodes’ location on the cross-section I would assume that ccx refers to one of those rather than their sum (maybe due to mpcs) when generating the output.

In my case the nodal numbering is a bit different, so ccx reports 125N in contrast to your 62.5N. So their is something wrong (but just for info: ABAQUS reporst RF=0.0 for the pre-tension node).

6

This simple model shows RF1=300 N (applied preload is 1200 N) if submitted in ccx 2.22 and RF1=1200 N if submitted in ccx 2.23:

*NODE
1, 0, 0, 0
2, 0, 0, 10
3, 0, 10, 0
4, 0, 10, 10
5, 10, 0, 0
6, 10, 0, 10
7, 10, 10, 0
8, 10, 10, 10
9, 0, 0, 20
10, 0, 10, 20
11, 10, 0, 20
12, 10, 10, 20
13, 0, 0, 0
*ELEMENT, TYPE=C3D8, ELSET=EALL
1, 4, 2, 1, 3, 8, 6, 5, 7
2, 10, 9, 2, 4, 12, 11, 6, 8
*NSET, NSET=FIXED
1, 3, 5, 7, 9, 10, 11, 12
*NSET,NSET=PREF
13
*NSET, NSET=PNSET
2, 4, 6, 8
*ELSET, ELSET=PELSET
1
*SURFACE, NAME=PSURF, TYPE=ELEMENT
PELSET, S3
*MATERIAL, NAME=STEEL
*ELASTIC
210000, 0.3
*SOLID SECTION, ELSET=EALL, MATERIAL=STEEL
*PRE-TENSION SECTION, SURFACE=PSURF, NODE=13
*STEP
*STATIC
*BOUNDARY
FIXED, 1, 6, 0
*CLOAD
13, 1, 1200
*NODE PRINT, NSET=PREF
RF
*NODE PRINT, NSET=PNSET
RF
*NODE FILE
RF, U
*END STEP

Forces from the nodes on the pretension surface are also printed. RF3 (preload direction) in each node there is actually -300 N.

7

OHH.:grinning_face: That was fixed silently at some point in this last version. 2.23.

Thank you very much. In some way it confirms there is a bug in previous version. Solved then.

Thanks.

8

As RF contains the external forces I guess solution should be:

RF = 1000N for Displacement Driven Preload.

RF = 0 N for Load Driven Preload.

Regards

EDITED: CCX 2.23 delivers 1000N in both cases. I guess it behaves like a REF node of a Rigid Body.

9

Yeah, it’s good to retest all GitHub bug reports just in case. Unfortunately, many are still relevant, from what I’ve noticed so far.

Yes, exactly.