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)
