# Truss element one direction

Hello,
is it possible,
to have truss elements for pressure or tension only?

wbr

It should be possible with tension-only and compression-only material (chapter 6.8.9 of Userâ€™s Manual).

Hi dichtstoff, Calc_em

ÂżWhat about a nonlinear Spring A. Could that do the job?
I have recently set up one and it works fine if you define the Reaction-Elongation curve wide enough.
It would have an asymmetric curve in tension and compression.

*SPRING,ELSET=Only_Tension_A,NONLINEAR

-0.1 ,-0.01000
0.0 ,0.00000
201.0 ,0.01000

Here you can see the response to an imposed positive and negative displacement. Linear in tension and â€śzeroâ€ť reaction force in compresion.

Elongation

Reaction

You could also use a GAPUNI element which is a compression- or tension-only spring. Since it has a rounded knee on its response curve, I guess it might perform better than the piecewise linear spring Disla suggested but you have to specify the direction with a vector instead of the nodes and it doesnâ€™t rotate with large displacements.

An interesting to try, can the model keep stable or not.

It seems to be right, i experiences a problem when max/min values defined is exceed the Solver acceptable limit based on load/deformation occurs. I did not yet investigate further, but a Gap element may solved this problem and limitation, can be general solution.

hello,

Iâ€™ll check the â€śgapâ€ť element.
Iâ€™m thinking to create or investigate a connection with screws,
where pressure is transferred directly between parts
tension and shearing force with an auxiliary construction.
wbr & thnx

Hello,

i have here now an example for the gap element.
What have i to do, that i can use the gap element for tension or pressure?
for what is the first value gap clearance? How must i use or set these value?

thnx for your help & support

``````**** EXAMPLE GAPUNI with PRESSURE and TENSION
Model: GAPUNI

*NODE, NSET=Nall
1,8.000000000000e+00,8.000000000000e+00,0.000000000000e+00
2,8.000000000000e+00,4.000000000000e+00,0.000000000000e+00
3,8.000000000000e+00,4.000000000000e+00,8.000000000000e+00
4,8.000000000000e+00,8.000000000000e+00,8.000000000000e+00
5,4.000000000000e+00,8.000000000000e+00,0.000000000000e+00
6,4.000000000000e+00,4.000000000000e+00,0.000000000000e+00
7,4.000000000000e+00,4.000000000000e+00,8.000000000000e+00
8,4.000000000000e+00,8.000000000000e+00,8.000000000000e+00
9,8.000000000000e+00,4.000000000000e+00,1.600000000000e+01
10,8.000000000000e+00,8.000000000000e+00,1.600000000000e+01
11,4.000000000000e+00,4.000000000000e+00,1.600000000000e+01
12,4.000000000000e+00,8.000000000000e+00,1.600000000000e+01
13,0.000000000000e+00,8.000000000000e+00,0.000000000000e+00
14,0.000000000000e+00,4.000000000000e+00,0.000000000000e+00
15,0.000000000000e+00,4.000000000000e+00,8.000000000000e+00
16,0.000000000000e+00,8.000000000000e+00,8.000000000000e+00
17,0.000000000000e+00,4.000000000000e+00,1.600000000000e+01
18,0.000000000000e+00,8.000000000000e+00,1.600000000000e+01
19,8.000000000000e+00,0.000000000000e+00,0.000000000000e+00
20,8.000000000000e+00,0.000000000000e+00,8.000000000000e+00
21,4.000000000000e+00,0.000000000000e+00,0.000000000000e+00
22,4.000000000000e+00,0.000000000000e+00,8.000000000000e+00
23,8.000000000000e+00,0.000000000000e+00,1.600000000000e+01
24,4.000000000000e+00,0.000000000000e+00,1.600000000000e+01
25,0.000000000000e+00,0.000000000000e+00,0.000000000000e+00
26,0.000000000000e+00,0.000000000000e+00,8.000000000000e+00
27,0.000000000000e+00,0.000000000000e+00,1.600000000000e+01
28,8.000000000000e+00,8.000000000000e+00,3.200000000000e+01
29,8.000000000000e+00,4.000000000000e+00,3.200000000000e+01
30,8.000000000000e+00,4.000000000000e+00,4.000000000000e+01
31,8.000000000000e+00,8.000000000000e+00,4.000000000000e+01
32,4.000000000000e+00,8.000000000000e+00,3.200000000000e+01
33,4.000000000000e+00,4.000000000000e+00,3.200000000000e+01
34,4.000000000000e+00,4.000000000000e+00,4.000000000000e+01
35,4.000000000000e+00,8.000000000000e+00,4.000000000000e+01
36,8.000000000000e+00,4.000000000000e+00,4.800000000000e+01
37,8.000000000000e+00,8.000000000000e+00,4.800000000000e+01
38,4.000000000000e+00,4.000000000000e+00,4.800000000000e+01
39,4.000000000000e+00,8.000000000000e+00,4.800000000000e+01
40,0.000000000000e+00,8.000000000000e+00,3.200000000000e+01
41,0.000000000000e+00,4.000000000000e+00,3.200000000000e+01
42,0.000000000000e+00,4.000000000000e+00,4.000000000000e+01
43,0.000000000000e+00,8.000000000000e+00,4.000000000000e+01
44,0.000000000000e+00,4.000000000000e+00,4.800000000000e+01
45,0.000000000000e+00,8.000000000000e+00,4.800000000000e+01
46,8.000000000000e+00,0.000000000000e+00,3.200000000000e+01
47,8.000000000000e+00,0.000000000000e+00,4.000000000000e+01
48,4.000000000000e+00,0.000000000000e+00,3.200000000000e+01
49,4.000000000000e+00,0.000000000000e+00,4.000000000000e+01
50,8.000000000000e+00,0.000000000000e+00,4.800000000000e+01
51,4.000000000000e+00,0.000000000000e+00,4.800000000000e+01
52,0.000000000000e+00,0.000000000000e+00,3.200000000000e+01
53,0.000000000000e+00,0.000000000000e+00,4.000000000000e+01
54,0.000000000000e+00,0.000000000000e+00,4.800000000000e+01

*ELEMENT, TYPE=C3D8, ELSET=Eall
1,     1,     2,     3,     4,     5,     6,     7,     8
2,     4,     3,     9,    10,     8,     7,    11,    12
3,     5,     6,     7,     8,    13,    14,    15,    16
4,     8,     7,    11,    12,    16,    15,    17,    18
5,     2,    19,    20,     3,     6,    21,    22,     7
6,     3,    20,    23,     9,     7,    22,    24,    11
7,     6,    21,    22,     7,    14,    25,    26,    15
8,     7,    22,    24,    11,    15,    26,    27,    17
9,    28,    29,    30,    31,    32,    33,    34,    35
10,    31,    30,    36,    37,    35,    34,    38,    39
11,    32,    33,    34,    35,    40,    41,    42,    43
12,    35,    34,    38,    39,    43,    42,    44,    45
13,    29,    46,    47,    30,    33,    48,    49,    34
14,    30,    47,    50,    36,    34,    49,    51,    38
15,    33,    48,    49,    34,    41,    52,    53,    42
16,    34,    49,    51,    38,    42,    53,    54,    44

*NSET,NSET=Ndis
36, 37, 38, 39, 44, 45, 50, 51, 54,

*NSET,NSET=Nfix
1, 2, 5, 6, 13, 14, 19, 21, 25,

*MATERIAL, NAME=EL
*ELASTIC
210000.,.3
*SOLID SECTION, ELSET=Eall, MATERIAL=EL

*ELEMENT, TYPE=GAPUNI, ELSET=G1
99,11,33

*SOLID SECTION, ELSET=G1, MATERIAL=EL
*GAP, ELSET=G1
0.5,0.,0.,1.

***ELEMENT,TYPE=T3D2,ELSET=ET3D2
**99,11,33

***SOLID SECTION,ELSET=ET3D2,MATERIAL=EL
**5

*BOUNDARY
Nfix,1,3,0
Ndis,3,3,-5
Ndis,1,1,0

*STEP, NLGEOM

*STATIC, SOLVER=SPOOLES

*NODE FILE, OUTPUT=3D
U

*EL FILE
S

*END STEP
``````

Initial clearance is usually zero. Stiffnesses can be set to extreme values (very high for compression and very low for tension) to simulate compression-only support.

What i have now as default is compression-only support!?:
*GAP, ELSET=G1
0.0,0.,0.,1.

how can i fix a tension-only support?

instead of gap as compression-only support i can
use a contact construction !?

wbr & thnx

Yes, by default GAP elements have large compressive stiffness and small tensile force (it could be lowered even more though).

Yes, compression-only support modeled with GAP elements is like contact with a rigid surface.

but how can i fix now a tension-only support?

Try with a very low compressive stiffness and high tensile force.

Hello Calc_em,

i want only a connection with tension,
thatâ€™s it,
but i think there is or will be no clear and easy auxiliary construction for me.
could there be a small hope, that in future in ccx
truss elements with tension and compression only could implemented!?

wbr dichtstoff and thnx for your help

Hello Disla,

i have tried gap element, but i think these is not suitable for me.
Is your auxiliary construction with spring also possible with a truss-element?

wbr & thnx

Do you mean only tension Springs like this?.

Isnâ€™t a truss, apart from aesthetic issues, the same as a Spring?. Whatâ€™s the difference?
I mean, both are hinged and meant to work as pure tension Âżisnâ€™t it?

Hello Disla,

for me truss elements are more convenient and usable.
For example to get the force, i use the stress command and the cross-section of the truss.
Working with ccx is very abstract and you have to work very carefull and step for step.
I donâ€™t use mecway but there it is more usable like ccx. (and mecway has a tension-only element)
Anyway, Iâ€™ll try spring element,
but Iâ€™ll test it first with a truss element, and then change it to spring element.
I like your example with tension-only elements.
Iâ€™ll go on and keep you up to date
wbr

Non linear spring is good and fast in modeling or convergences, however a general curve need to seek and adjust to be working in any loading case and intensity. Another issue previously i found is in connected to layered shell element. So, i will try using Gap element first to modeling support and nonlinear Spring as alternative. In case of truss with limited capacity in tension or compression, it seems beam element with end rotation released by equation will work better and represent well.

The tension on a hinged only tension element should also be directly available through the elongation of the member. Regarding the only tension element in Mecway I donâ€™t really know whatâ€™s behind. It is under the internal solver and there are important differences in shell and beam formulations.

NL springA works fine.Give it a chance and check if it can cover your needs. Keep in mind this is a material nonlinearity.

``````** Generated by Mecway 19.0
*NODE
1,0.008,0.008,0
2,0.008,0.004,0
3,0.008,0.004,0.008
4,0.008,0.008,0.008
5,0.004,0.008,0
6,0.004,0.004,0
7,0.004,0.004,0.008
8,0.004,0.008,0.008
9,0.008,0.004,0.016
10,0.008,0.008,0.016
11,0.004,0.004,0.016
12,0.004,0.008,0.016
13,0,0.008,0
14,0,0.004,0
15,0,0.004,0.008
16,0,0.008,0.008
17,0,0.004,0.016
18,0,0.008,0.016
19,0.008,0,0
20,0.008,0,0.008
21,0.004,0,0
22,0.004,0,0.008
23,0.008,0,0.016
24,0.004,0,0.016
25,0,0,0
26,0,0,0.008
27,0,0,0.016
28,0.008,0.008,0.032
29,0.008,0.004,0.032
30,0.008,0.004,0.04
31,0.008,0.008,0.04
32,0.004,0.008,0.032
33,0.004,0.004,0.032
34,0.004,0.004,0.04
35,0.004,0.008,0.04
36,0.008,0.004,0.048
37,0.008,0.008,0.048
38,0.004,0.004,0.048
39,0.004,0.008,0.048
40,0,0.008,0.032
41,0,0.004,0.032
42,0,0.004,0.04
43,0,0.008,0.04
44,0,0.004,0.048
45,0,0.008,0.048
46,0.008,0,0.032
47,0.008,0,0.04
48,0.004,0,0.032
49,0.004,0,0.04
50,0.008,0,0.048
51,0.004,0,0.048
52,0,0,0.032
53,0,0,0.04
54,0,0,0.048
*ELEMENT,TYPE=C3D8
1,1,2,3,4,5,6,7,8
2,4,3,9,10,8,7,11,12
3,5,6,7,8,13,14,15,16
4,8,7,11,12,16,15,17,18
5,2,19,20,3,6,21,22,7
6,3,20,23,9,7,22,24,11
7,6,21,22,7,14,25,26,15
8,7,22,24,11,15,26,27,17
9,28,29,30,31,32,33,34,35
10,31,30,36,37,35,34,38,39
11,32,33,34,35,40,41,42,43
12,35,34,38,39,43,42,44,45
13,29,46,47,30,33,48,49,34
14,30,47,50,36,34,49,51,38
15,33,48,49,34,41,52,53,42
16,34,49,51,38,42,53,54,44
*ELEMENT,TYPE=SPRINGA
17,11,33
*NSET,NSET=NALL
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
*NSET,NSET=NDIS
36
37
38
39
44
45
50
51
54
*NSET,NSET=NFIX
1
2
5
6
13
14
19
21
25
*ELSET,ELSET=EALL
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
*ELSET,ELSET=SP_A
17
*MATERIAL,NAME=EL
*ELASTIC,TYPE=ISOTROPIC
210000,0.3
*SOLID SECTION,ELSET=EALL,MATERIAL=EL
*BOUNDARY
1,1,,0
1,2,,0
1,3,,0
2,1,,0
2,2,,0
2,3,,0
5,1,,0
5,2,,0
5,3,,0
6,1,,0
6,2,,0
6,3,,0
13,1,,0
13,2,,0
13,3,,0
14,1,,0
14,2,,0
14,3,,0
19,1,,0
19,2,,0
19,3,,0
21,1,,0
21,2,,0
21,3,,0
25,1,,0
25,2,,0
25,3,,0
36,1,,0
37,1,,0
38,1,,0
39,1,,0
44,1,,0
45,1,,0
50,1,,0
51,1,,0
54,1,,0
*AMPLITUDE,NAME=A_1
0,0
0.01,-1.06581427417E-18
0.25,-0.0050000008
0.49,-1.06581427417E-18
0.51,1.06581427417E-18
0.75,0.0050000008
0.99,1.06581427417E-18
1,0
*SPRING,ELSET=SP_A,NONLINEAR

-0.000001 ,-1.0
0.0 ,0.0
10000.0 ,.01

*STEP,NLGEOM=YES,INC=110,AMPLITUDE=STEP
*STATIC
0.01,1,0,0.01
*BOUNDARY,AMPLITUDE=A_1
36,3,,1
*BOUNDARY,AMPLITUDE=A_1
37,3,,1
*BOUNDARY,AMPLITUDE=A_1
38,3,,1
*BOUNDARY,AMPLITUDE=A_1
39,3,,1
*BOUNDARY,AMPLITUDE=A_1
44,3,,1
*BOUNDARY,AMPLITUDE=A_1
45,3,,1
*BOUNDARY,AMPLITUDE=A_1
50,3,,1
*BOUNDARY,AMPLITUDE=A_1
51,3,,1
*BOUNDARY,AMPLITUDE=A_1
54,3,,1
*NODE FILE,GLOBAL=YES
U,RF
*EL FILE
S,NOE,E
*END STEP

``````

I have now an example with a truss element.

Force is 100N x 9 nodes = 900
so i get stress SZZ 900/ 5 = 180 and these is what i have with SZZ.
length of truss is 16, area section is 5,
so i get a spring constant k = E x A / L = 210000 x 5 / 16 = 65625 N/mm
How can i change now to *SPRINGA ?

*ELEMENT,TYPE=SPRINGA,ELSET=ESPRINGA
99,11,33
*SPRING,ELSET=ESPRINGA
???.

What is my result?

``````**** EXAMPLE TRUSS with PRESSURE and TENSION
Model: Truss tension-compression-only

*NODE, NSET=Nall
1,8.000000000000e+00,8.000000000000e+00,0.000000000000e+00
2,8.000000000000e+00,4.000000000000e+00,0.000000000000e+00
3,8.000000000000e+00,4.000000000000e+00,8.000000000000e+00
4,8.000000000000e+00,8.000000000000e+00,8.000000000000e+00
5,4.000000000000e+00,8.000000000000e+00,0.000000000000e+00
6,4.000000000000e+00,4.000000000000e+00,0.000000000000e+00
7,4.000000000000e+00,4.000000000000e+00,8.000000000000e+00
8,4.000000000000e+00,8.000000000000e+00,8.000000000000e+00
9,8.000000000000e+00,4.000000000000e+00,1.600000000000e+01
10,8.000000000000e+00,8.000000000000e+00,1.600000000000e+01
11,4.000000000000e+00,4.000000000000e+00,1.600000000000e+01
12,4.000000000000e+00,8.000000000000e+00,1.600000000000e+01
13,0.000000000000e+00,8.000000000000e+00,0.000000000000e+00
14,0.000000000000e+00,4.000000000000e+00,0.000000000000e+00
15,0.000000000000e+00,4.000000000000e+00,8.000000000000e+00
16,0.000000000000e+00,8.000000000000e+00,8.000000000000e+00
17,0.000000000000e+00,4.000000000000e+00,1.600000000000e+01
18,0.000000000000e+00,8.000000000000e+00,1.600000000000e+01
19,8.000000000000e+00,0.000000000000e+00,0.000000000000e+00
20,8.000000000000e+00,0.000000000000e+00,8.000000000000e+00
21,4.000000000000e+00,0.000000000000e+00,0.000000000000e+00
22,4.000000000000e+00,0.000000000000e+00,8.000000000000e+00
23,8.000000000000e+00,0.000000000000e+00,1.600000000000e+01
24,4.000000000000e+00,0.000000000000e+00,1.600000000000e+01
25,0.000000000000e+00,0.000000000000e+00,0.000000000000e+00
26,0.000000000000e+00,0.000000000000e+00,8.000000000000e+00
27,0.000000000000e+00,0.000000000000e+00,1.600000000000e+01
28,8.000000000000e+00,8.000000000000e+00,3.200000000000e+01
29,8.000000000000e+00,4.000000000000e+00,3.200000000000e+01
30,8.000000000000e+00,4.000000000000e+00,4.000000000000e+01
31,8.000000000000e+00,8.000000000000e+00,4.000000000000e+01
32,4.000000000000e+00,8.000000000000e+00,3.200000000000e+01
33,4.000000000000e+00,4.000000000000e+00,3.200000000000e+01
34,4.000000000000e+00,4.000000000000e+00,4.000000000000e+01
35,4.000000000000e+00,8.000000000000e+00,4.000000000000e+01
36,8.000000000000e+00,4.000000000000e+00,4.800000000000e+01
37,8.000000000000e+00,8.000000000000e+00,4.800000000000e+01
38,4.000000000000e+00,4.000000000000e+00,4.800000000000e+01
39,4.000000000000e+00,8.000000000000e+00,4.800000000000e+01
40,0.000000000000e+00,8.000000000000e+00,3.200000000000e+01
41,0.000000000000e+00,4.000000000000e+00,3.200000000000e+01
42,0.000000000000e+00,4.000000000000e+00,4.000000000000e+01
43,0.000000000000e+00,8.000000000000e+00,4.000000000000e+01
44,0.000000000000e+00,4.000000000000e+00,4.800000000000e+01
45,0.000000000000e+00,8.000000000000e+00,4.800000000000e+01
46,8.000000000000e+00,0.000000000000e+00,3.200000000000e+01
47,8.000000000000e+00,0.000000000000e+00,4.000000000000e+01
48,4.000000000000e+00,0.000000000000e+00,3.200000000000e+01
49,4.000000000000e+00,0.000000000000e+00,4.000000000000e+01
50,8.000000000000e+00,0.000000000000e+00,4.800000000000e+01
51,4.000000000000e+00,0.000000000000e+00,4.800000000000e+01
52,0.000000000000e+00,0.000000000000e+00,3.200000000000e+01
53,0.000000000000e+00,0.000000000000e+00,4.000000000000e+01
54,0.000000000000e+00,0.000000000000e+00,4.800000000000e+01

*ELEMENT, TYPE=C3D8, ELSET=Eall
1,     1,     2,     3,     4,     5,     6,     7,     8
2,     4,     3,     9,    10,     8,     7,    11,    12
3,     5,     6,     7,     8,    13,    14,    15,    16
4,     8,     7,    11,    12,    16,    15,    17,    18
5,     2,    19,    20,     3,     6,    21,    22,     7
6,     3,    20,    23,     9,     7,    22,    24,    11
7,     6,    21,    22,     7,    14,    25,    26,    15
8,     7,    22,    24,    11,    15,    26,    27,    17
9,    28,    29,    30,    31,    32,    33,    34,    35
10,    31,    30,    36,    37,    35,    34,    38,    39
11,    32,    33,    34,    35,    40,    41,    42,    43
12,    35,    34,    38,    39,    43,    42,    44,    45
13,    29,    46,    47,    30,    33,    48,    49,    34
14,    30,    47,    50,    36,    34,    49,    51,    38
15,    33,    48,    49,    34,    41,    52,    53,    42
16,    34,    49,    51,    38,    42,    53,    54,    44

*NSET,NSET=Ndis
36, 37, 38, 39, 44, 45, 50, 51, 54,

*NSET,NSET=Nfix
1, 2, 5, 6, 13, 14, 19, 21, 25,

*MATERIAL, NAME=EL
*ELASTIC
210000.,.3
*SOLID SECTION, ELSET=Eall, MATERIAL=EL

*ELEMENT,TYPE=T3D2,ELSET=ET3D2
99,11,33

*SOLID SECTION,ELSET=ET3D2,MATERIAL=EL
5

*STEP

*STATIC, SOLVER=SPOOLES

*BOUNDARY
Nfix,1,3,0
Ndis,1,2,0