Creep and Shrinkage

Question:

I have a very simple concrete plate model with one 19 strand tendon.  I am trying to use the construction stage analysis to determine losses in the post-tensioning tendon.  If I place a duration of more than 10 days for the only construction stage (CS1) the analysis will stop completely and I will get no results.  I need to determine long term stress losses on a more complicated concrete plate model but I cannot even make a simple model give me the desired results.  Please provide insight as to why I cannot attain the long term stress losses.  I have attached the file containing my simple I-girder model.


Thank you.




Answer:

Hi,

There are some inputs to be corrected in this model.
1. Time Dependent Materials (Creep, Shrinkage, compressive strength) are assigned to the dummy beam. Change it to tendon material.
2. Concrete age of plate elements is zero when they are activated, which means that the plate elements will have almost zero rigidity.
3. Change the 'Tendon Tension Loss Effect' option from 'Change with variation of tendon force' to 'Constant'.

4. Delete 'Approximate Tendon Loss' data. You have defined Time Dependent Materials by which exact prestress loss will be calculated. So, 'Approximate Tendon Loss' data should be removed.

Now, the analysis runs successfully. Please find the attached file for your reference.

Regards,
DK


Thank you DK.  I was unable to run the file you sent as I need to upgrade my version of Midas Civil.  I tried your recommendations in my file in the 2017 version and the program did run for a construction stage greater than 10 days however the C & S losses were 0.0.  It looks like I will need to wait until tomorrow for the upgrade to 2019.  I will let you know if I cannot get the file you sent to work.  Thanks again.

DK,

I upgraded to Midas Civil 2019 and ran the file you sent.  The losses for creep and shrinkage are coming out as 0.0.  Please advise.  Thanks.



Hi,

The C & S losses are also zero in the latest version. The reason for this is that we did not assign time dependent material (creep & shrinkage) to the beam elements to which tendon is assigned. If we assign time dependent material to the beam elements, the analysis is terminated because the section of beam elements is very small, which causes the divergence of creep calculation of beam elements.

Regards,
DK 


DK,


Does Midas Civil calculate creep and shrinkage for beam elements only and not for plate elements?


Thanks,



Creep and shrinkage are calculated for the plate element as well. But, the loss due to creep and shrinkage is only calculated for the beam element to which tendon is assigned.

Regards,
DK


DK,


Thank you.  I understand now.

Creation date: 8/15/2018 8:57 PM (dklee@midasit.com)      Updated: 8/16/2018 6:29 AM (dklee@midasit.com)
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180809 SIMPLE I GIRDER.mcb
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