Topic: Switch from unbonded to bonded reinforcements

I would like to simulate (in ATENA 3D Engineering) the construction phases of a prestressed concrete element, by reproducing the following steps:

Step 1) I define a concrete macroelement;

Step 2) I define some reinforcement bars (called "primary reinforcements") and I apply to these elements a pre-stressing load, in this step the bars are unbonded so I would like to simulate this behaviour;

Step 3) The reinforcements become bonded, but i don't know how i can reproduce the change of behaviour from unbonded to bonded (i've tried to define a bond material with very low properties for the unbonded phase and to switch to a perfect bond for the second phase, but it seems that the software doesn't allow to change the bond law once it is defined for the previous construction phase);

Step 4) I define addictional bars (called "secondary reinforcements") and I try to repeat the same steps made for the primary reinforcements.

I've made several attempts to reproduce this behaviour but i still can't reproduce the switch from unbonded reinforcements to bonded. How can I do to solve this issue?

In addition, I would like to know if, in a construction phase, is it possible to remove elements (added previously) or if is it possible (always in a construction phase) to change the type of an element e.g. from external cable to reinforcement bar. I've tried to do both but somthing seems to don't work.

Thank you in advance for your help.

Re: Switch from unbonded to bonded reinforcements

Dear DLM,
I. I recommend to fist see ATENA Troubleshooting, 2.2.5 How to model bonded post-tensioning cables in ATENA?
You may be interested in the (relatively new) option "Internal Cable".

II. For an introduction in representing construction process in ATENA, please see Troubleshooting, 2.2.1 Is there an example how to change the structure during analysis to consider the construction process?

III. If you decide to work with ATENA Science, please see the description for the Condition "Elements activity" (section 5.2 Conditions) and "Show Material Activity" in Interval Data (see also ATENA-GiD User's Manual, Fig. 5-81 Interval Data window – Material activity), and the help bubbles in the corresponding dialogs.

For adding reinforcements later during the analysis, please see the option "Application from Interval", see also the ATENA-GiD User's manual, Fig. 5-64: 1D Reinforcement material properties – Element Geometry, and again the corresponding help bubbles.

Regards.

Re: Switch from unbonded to bonded reinforcements

Dear dpryl,

Thank you for your answer.
I've already read the troubleshooting sections 2.2.1 and 2.2.5 but now I switched to ATENA Science + GiD.

Before simulating the test described in my previous post I decided to try to model a simpler one:

Basically, I would like to simulate the stress migration from a cable (that reaches the design prestressing force in two different steps (1 and 4) to the surronded concrete, casted (step 2) after the initial prestressing of the cable (step 1).
In particular, I have a first stage (step 1) in which I apply an amount of prestressing to the unbonded cable, in the second stage (step 2) I cast the concrete element around the cable, then in the third phase (step 3) I inject the duct (and the cable becomes bonded) finally, at the last stage (step 4), I apply additional prestressing to the cable to compress the concrete.

In these condition, having applied some force to the cable in stage 4, what I'm expecting is to have a re-distribution of this stress between cable and concrete.

I tried to obtain this result in several ways but no one seems to correctly work; in particular I made these tests:

1)I tried to switch the behaviour of the internal cable from not injected to injected (both with perfect bond and with a generic bond law) but it seems not possible to change the material law for a reinforcement bar from an interval to the following one;
2)I tried to introduce the concrete in the third stage by defining a fictitious soft material adopted for stages 1 and 2 and by changing the material with the actual one at the beginning of the stage 3;
3.1)I tried to simulate the injection by introducing two different volumes [the first one around the bar (in order to have a prism around the entire length of the cable), the second one around the prism] and then by connecting these 2 volumes with interfaces having a material (interface) that changes
from the stage 2 to stage 3 to simulate the injection of the duct;
3.2)I tried to reproduce the same test of point 3.1 by deleting the bar and by applying the force directly to the internal prism.

In all these tests i tried to apply the prestressing by means of several ways by using the following commands:
-"Prestressing for Reinf Line" or "Initial Stress for Reinf Line" for cases 1-2-3.1;
-"Load Force for Surface" for case 3.2.

I'm not able to reproduce properly the migration of the stress; further I have a lot of convergence issues, even if I am using only elastic materials except for the cable (but it is working in the elastic part of its strain-stress diagram, so basically all the elements are elastic).

Thank you in advance for your help, I am available to give you further details or, if you prefer, I can send you all these files.

Best regards,
   Dario

Re: Switch from unbonded to bonded reinforcements

Dear Dario,
I. I suggest to first try the simplest approach, i.e., a bar with perfect bond + applying the prestressing as Initial Strain for Reinforcement. The casting sequence seems quite similar to the traditional wire prestressing where the wires are cut at form removal, which is usually well represented this way. Moreover, as you mention prestressing the cable before casting the concrete, I guess the cable channel is straight (not curved nor bent at some points), which means the frictional losses are not likely to be of interest.

That means steps 1-3 can be covered in a single Interval, Step 4 = additional prestressing can be applied in Int 2, again as (additional) Initial Strain.

II. If the above shows not good enough, please look at the example model demonstrating injected cables which is installed with ATENA: %Public%\Documents\ATENA Examples\Science\GiD\Tutorial.Static3D\BondCabel_Injected.gid

III. If you still have problems and need help with your particular model, you can follow Troubleshooting, 2.1.1 to send us your mdoel etc.

Regards.

Re: Switch from unbonded to bonded reinforcements

Hi Dario,

It seems that your first approach was correct but you used wrong tool.

DLM wrote:

1)I tried to switch the behaviour of the internal cable from not injected to injected (both with perfect bond and with a generic bond law) but it seems not possible to change the material law for a reinforcement bar from an interval to the following one;

Probably you tried to change material in dialog "Interval data" while it is not applicable to rebars. I recommend you to check demo model which Dobromil mentioned and read Tutorial for construction process.

If you use Reinforcement Inactivity for Line condition it has to work. See this picture as example: https://drive.google.com/open?id=1se4-2 … cpM9lqYSFG