Initial stress for prestressing

[mari.95]

Hello to everyone, I have some questions.
I created a reinforced concrete beam, which is modeled with solid for concrete and beam element for rebars. I used node-to-element interaction to create the embedded constraint between concrete and rebars. Today I add a tendon in order to validate the model also using prestressing. I use also a beam element for tendon, embedded constraint and I assign the initial stress to the tendon. My first question is: Does Stko apply automatically the initial condition without the necessity of doing a stage analysis? And If I want to do stage analysis where in the first analysis I have the initial condition and in the second one the load, is there the memory of the initial state?
Then: Does Stko calculate prestressing losses, such as the friction loss and the anchorages one, just with the information of materials (damageTC3D for concrete and steel02 for tendon) and interactions? Thanks in advance and sorry if my questions are trivial, I'm not an expert user.

Mari

[STKO Team]

Thanks in advance and sorry if my questions are trivial

Actually, they are not trivial at all...

Does Stko apply automatically the initial condition without the necessity of doing a stage analysis? And If I want to do stage analysis where in the first analysis I have the initial condition and in the second one the load, is there the memory of the initial state?

You should first run an analysis with just 1 step, without any load, so that this analysis will just compute the effect of initial-stress in the tendons.
After this analysis you can apply external loads and proceed with other analyses. Of course OpenSees always keeps memory of what happened in previous analyses.

Just keep in mind that the effect of initial-stress is applied instantaneously, that's why you don't need more that 1 step. This should not be a problem, because the effect of pre-stress should not push your structure into an highly nonlinear stage.
If this happens, there is a way to apply pre-stress incrementally, but it's quite cumbersome, so I will explain it to you only if you really need it.

Does Stko calculate prestressing losses, such as the friction loss and the anchorages one, just with the information of materials (damageTC3D for concrete and steel02 for tendon) and interactions?

Yes and now... it really depends.. What OpenSees compute automatically is the stress transferred to the concrete from the tendond, thanks to the embedded constraint. But the slippage / friction loss at the interface between tendon and concrete is not modelled, so OpenSees cannot calculate it.
We will prepare an extension to the ASDEmbeddedCondition for the next webinar, where we will add the possibility to add a nonlinear axial interface between the embeeded beam and the solid

[mari.95]

Ok, thanks a lot for the clarifications. So if I understood correctly I should carry out a stage analysis in which in the first analysis I have no loads, (linear algorithm with a single step) then I add the loads and perform the second analysis, as is shown in the picture attached. Is it correct? And then can I made this also using parallel analysis, using Openseesmp?

[STKO Team]

I should carry out a stage analysis in which in the first analysis I have no loads, (linear algorithm with a single step) then I add the loads and perform the second analysis

Correct, but do not use Linear algorithm, your problem is nonlinear anyway!

And then can I made this also using parallel analysis, using Openseesmp?

Yes

[mari.95]

Thank you very much.

[STKO Team]

You are welcome! =)