Pre-stressed curved beam

(Simonerutigliano) #1


For my Master’s Thesis research I’m searching the optimal shape of an arch with a given pre-stress.
I think that the analysis method implemented into Kiwi3D could be very helpful in this case.

I’m looking for the best way to define the prestress for a given “beam” element.
I tried to set the prestress as a list of four values, (I think these four values represent the amount of prestress on the vertex of the cross-section) assuming values in kN. Perhaps I assume (10, 10, 10, 10) as a pre-stress due to a cable along the centroid axis.

So, I consider negligible mass, so I don’t have gravity load, but I would like to see only the effect due to the prestress, in this case uniformely compressed, but I get 0 as Normal stress on the beam element.

Alternatively I was considering to couple, if it’s possible and would make any sense, the cable element with the beam element. But as I see is possible set the pre-stress directly inside the “beam” component I think there should be some issue. (16.9 KB)

If there is someone able to help me, would be really appreciated.
Thank you very much for the support.

(Anna) #2

Kiwi!3d basically used the prestress options of the beam until now only for an automatic derivation of the prestresses by assuming straight and non-twisted initial configuration of the beam. The application of pre-defined prestresses by the user will be fully available in the next update by the end of January. However, it can only be used in a non-linear analysis. The input format is unfortunately still a little bit cumbersome as it is an advanced option. The first 4 numbers define which prestress should be used (0: no prestress, 1: user-defined prestress, 2=automatic prestress). The following numbers are then a list of the user-defined values. So you need a list (1,1,1,1,10,10,10,10) for your problem. With this you get a normal force of 10, bending moment 1 and 2 of 10 and torsional moment of 10. The unit will be in your chosen unit, so e.g. 10kN, 10kNm, 10kNm, 10 kNm.

(Simonerutigliano) #3

It will be possible apply the pre-stress on curved elements? Like curved beam, curved shells?
Still doesn’t works in this way.

(Anna) #4

it WILL work in this way in the updated version coming in the end of the week with non-linear analysis.

you will then be able to use it for straight and curved beams. Shells with (automatic) prestress are still in development.

(Anna) #5

The new version Kiwi!3D Beta 0.2.0 is now available!

(Simonerutigliano) #6

Hi, thank you for sharing the update.
I tried again with the new version of the plug-in. Adding the pre-stress in the beam component, I’m still not able to get any good result for normal stress N. Quite strange. Could you, kindly, have a look to the attached definition? Many thanks for the support. (26.7 KB)

(Anna) #7


there were basically 3 things:

  1. The output settings in order to output stresses for non-linear analysis was missing
  2. Arcs with an angle > Pi/2 have to be rebuild in order to avoid the c0-continuity in the middle. This c0 continuity in the beam acts like a joint. Therefore, the system in this file was kinematic and the solution is arbitrary. (An automatic fix of this in order to avoid the rebuild may be part of the next release. Alternatively, you can also use two arcs <= Pi/2. They will then automatically be coupled with a joint which can resist moments)
  3. (The Young’s modulus was really large. This can cause numerical errors)

With this changes you should get the defined prestresses for LC 0. For higher LC this forces may vanish due to boundary conditions.

I also added this changes to your grasshopper file. The changes with small comments are in the blue boxes. (20.9 KB)

(Simonerutigliano) #8

Many thanks!