post-tensioning bars

[Zouatine]

Dear all,

I hope you are doing well,

I'm trying to model a post-tensioning bar in my structure in Etabs as is shown in the figure, unfortunately, I'm not able to find the option of modeling a post-tensioning strand in the software, I was thinking if I can model them as external Tendons if no would you please give me any thoughts about how to model that?

thank you

 

[Trenno]

I think Agent's recommendation is the way to go, using an initial temperature load case to induce the pretension, then using this global stiffness matrix at the starting point for all other load cases.

So... what's the diameter of the cable, material and what initial pretension force do you want to achieve?

Agent - how do you define a non-linear compression only spring (gap)spring in this case within SAP2000? Does it need to be a link between two joints (ie a joint sitting somewhere below the lower columns)? I had a quick play around with the problem at hand but couldn't get the gap link to work properly. It's slightly easier in ETABS where you can define a compression only spring directly.

 

[Zouatine]

Dear all,

Thank you for your cooperation as Mr. Agent666 said that I'm trying to design a rocking frame structure in Etabs, as it considered as high performance against the earthquake loading, first we do provide a PT bar along with the height of the column in order to make a restoring moment to self-center the frame when it is rocking as well as energy dissipation devices, as you said Mr. Agent666 that I have to free the support at the base this is just the start of the model so I'm taking a global idea about how can I do the design.

Mr. Trenno about the diameter of the cable some pre-calculation is needed, it is taken from the dissertation of Roke et al 2010 in lehigh university, they did mention how to determine the diameter which depends on the Overturning moment at different performance objectives.

I didn't go that deep into it when I was asking the question because I was afraid that my idea or method that I'm applying is not clear yet.

Respected Mr. Agent666, while I'm looking in the official website of the Etabs, and as you said to limit the compression limit, but I got confused since I'm doing Response Spectrum Analysis of the structure and it is mentioned in the method of the design for the rocking frame all the members should remain elastic, it is one of the objectives for the design of the Rocking frame.

however Respected Sir, do you think that I have to switch to SAP 2000 and design the PT bars as cable?

thank you, I'm waiting for your kind reply,

 

[r13]

The linked paper was written by the developers of this innovative technology, that might provide some help other than modeling. Link

 

[Zouatine]

Dear Mr r13,

Thank you for your help, I went through all the research papers in order to understand the behavior of the system as well as the research paper that you mentioned ,

Now i got stuck in modelling different part of the structure element, like PT bars and energy dissipation element,

Let's wait the answer of the other engineers hope my issue will be solved.