Hi,
I’ve seen some requests for an option to turn the compression-only constraint into a tension-only constraint. PrePoMax determines the direction vector automatically and sets it for compression but an option to invert it could be useful. Example:
*Gap, Elset=Compression_Only-1_ElementSet1
0, 0, 1, 0, , 250000000000, 0.00025
*Gap, Elset=Compression_Only-1_ElementSet1
0, 0, -1, 0, , 250000000000, 0.00025
good news, it seems to be possible in CalculiX to reverse the direction to make it tension only support.
*Gap, Elset=Compression_Only-1_ElementSet-18
0, 0, 0, -1, , 25000, 2.5E-05
*Gap, Elset=Compression_Only-2_ElementSet-1
0, 0, 0, 1, , 50000, 5E-05
*Gap, Elset=Compression_Only-1_ElementSet-18
0, 0, 0, -1, , 25000, 2.5E-05
*Gap, Elset=Compression_Only-2_ElementSet-1
0, 0, 0, -1, , 50000, 5E-05
Yes, I tested this on the cube model from my first post. Initially, I thought that it’s enough to specify very low spring stiffness and large tensile force but it doesn’t work this way. The direction has to be reversed.
previously, i’m facing similar problem also then go to nonlinear spring element instead of gap. However, these elements type have some limitation i.e force-deformation curve and geometry need to satisfy for compression only types. Maybe for the future of implementation in PrePoMax is required due to stiffness nonlinearity advantages.
For what purposes would one use a tension only support where a normal BC not sufficient?
This is sometimes used in civil engineering and thus available in software meant for such applications.
https://www.lusas.com/user_area/faqs/tension_only_members.html
probably it’s widely used for single point spring of tension only, shown as example below. Anchor rods can have several configurations which only resist tension forces subjected to any overturning moment directions. Steel baseplate is supported by compression only springs currently available in PrePoMax. Both support constraint models possible to set the stiffness in CalculiX, however still limited in elastic force-deformation curves. There’s another approach for these condition using compression/tension only by two nodes of nonlinear spring element
image from Morgan (2018)
in civil engineering (pole design to replace steel ropes/cables which works only in tension)
Exactly, SOFISTIK also having the possibilty to use tension or compression springs only.
@synt:
Can you explain how to work with tension only springs?
For compression only we could use the compression only feature in prepomax.
it has been explained in the beginning by reversed direction of gap element, i’m just taking simple test. To not be confused, external software such as SAP2000 naming these elements as Hook since working in tension only. Both of them are limited to linear in stiffness, need to use two node spring in case of non-linear.
Tension only features being proposed, not yet available in PrePoMax, some work around by copy to modify in Keyword Editor.
Only tension works with custom cards, but I could not find the way to create isolated nodes on the screen.
I’m building springs in between two elements for the example. It requires nonlinear analysis.
as i know, Compression or Tension only in PrePoMax implementation using gap element may be similar to external software noticed, since large deformation can deactivate or not. However, two nodes nonlinear spring element is required nonlinear geometry activated and mandatory, large deformation may cause membrane effect and problem in stability of thin part.
I want to create Tension only springs to surfaces of baseplates to simulate exactly what you picture shows from Morgan 2018.
Basicly the baseplatte has surface areas of the washer sizes, which i want to select.
If anybody can explain my how to work with custom cards it would be helpfull. May this feature comming soon in prepomax.
it can be shown and copied. However, export to CalculiX Inp files for further editing seems more convenient.
indeed, draw or define spring by two nodes selected also.
Yeah, the easiest way might be to export the .inp file (File → Export → CalculiX *.inp) and manually do the change explained in the OP here: Tension-only constraint
but this can be simple by direct assigned at top surface in washer by partition, some limitation in anchor bolt shear and bending being ignored.
Recall nonlinear activation is mandatory for any of this approaches to work properly (springs or gap elements).
If not active, behavior will not be ONLY tension. Without NLGEOM Surface stiffness will be reduced to 1/2 the user input and gap elements will work in both directions ( tension AND compression) as a regular Surface Spring behavior.
Nonlinear behaviour —>Nonlinear analisys.
Compression only have specific setting, it seems NLGeom is not mandatory. Previously noticed about fictitious or fake contact, i’m not known in details but just shown work.
That option adds dummy nonlinear material with:
*Material, Name=Internal_compression_only-1
*Density
1
*Elastic
1, 0
*Plastic
0, 0
what constraint did you take for the yellow washer areas?
I would like to give them surface spring with tension only.
Currently i am just giving them for example a surface spring with Z direction for example 100000N/mm and Y und X like 1000N/mm.