Beam prestressed

Grasshopper Karamba3D
1

Hello, I had a question about the work I’m doing. I’ve reproduced a bridge that already exists in reality and I need to analyze it. It’s a rather special bridge because it’s made of two different materials: the first is granite in the form of block, the second is a series of 5 steel bars that are pre-stressed. The problem is that I’d like to bind these two materials together, so that they become one, with one compensating for the other in tension and the other in compression. I’ve seen that there’s a box for prestressing the steel bars, but I don’t know if it makes much difference to the final result.

2

Hi, what is the exact question that you have?

3

Hello, thank you for your quick reply. My question is whether it’s possible to assemble two different materials together (granite block with prestressed steel inside) with different geometries. In my case, when I apply a force to my beam, the two materials deform independently of each other, whereas they should deform together.

So my questions are:

  • how do you assemble two different materials together so that they deform together?
  • how does the prestressing box work?
  • how does the box work for thermal expansion (because steel and granite have to different thermal coefficient so it would be very interesting to use that)?

Thank you

4

Hello @Simon_Honorez,

  1. Currently (Karamba3D V3.1.4) the best way to do this is to use two different sets of beam elements - one for the granite block, one for the steel and provide a shear-stiff connection between them. This could look like a truss.
  2. The prestressing can be done via an InitialStrain-Load.
  3. The thermal expansion can be controlled via the material’s thermal expansion coefficient alphaT and a temperature-load.

– Clemens

5

hello, I’m coming back to you but I don’t understand how to ensure a shear-resistant connection between them?

6

You connect them via springs (see here).
– Clemens

7

I’m having some issues implementing prestressing in Grasshopper and was hoping for advice.

I’ve successfully modelled a prestressed pin‑jointed steel truss where I can control the force in a member using the Initial Strain load, and I’ve attached a small example definition below:

prestressed_steel truss.3dm (49.1 KB)

prestressed_steel truss.gh (39.7 KB)

My problem is extending this to a concrete strut in a statically indeterminate strut‑and‑tie model.

What I’m looking for is a way to control the compression force in a concrete strut while still enforcing deformation compatibility at the node, so the displacement reflects the combined axial stiffness of the prestressed member within the global system.

Has anyone implemented a prestressed concrete strut/member in Karamba and is willing to share a definition? Any guidance would be appreciated.

8

Hi @stia,

did you try to place two beams on top of each other - one out of concrete, the other one representing the prestressed steel wires?

– Clemens