prestress loss to Eurocode with time dependent material

Question:

Hi,
I am working on a model with construction stage analysis and time dependent materials of a prestressed concrete integral bridge. 

It is not clear if the software calculates automatically the loss of prestress in the tendons in accordance with the relationship set up for time dependent materials (Eurocodes in my case) or if I have to set up also the "Approximate tendon losses" (which does not have Eurocodses as an option) in the analysis tab to have a result from Midas about the loss of prestress.

Apparently prestress losses due to creep, shrinkage and elastic shortening of concrete are automatically calculated in the construction stage analysis (settings can be checked by clicking "time dependent effect control" in the "construction stage analysis data" tab. 

In light of the above, it is not clear if the "Approximate tendon losses" is needed just to have a result about relaxation of steel.

My questions are:
1 - Does Midas give as an output the loss of prestress also without setting up the "approximate tendon losses" analysis? And if yes, are these results related to time dependent materials only (i.e. concrete only)?
2 - If the answer to question 1 is yes, are the results given in accordance to the standards to which the time dependent effects have been set up? (Eurocodes in this case)?
3 - Is there a way to have an output from Midas on complete prestress losses in accordance to Eurocodes for the construction stage analysis?

Thanks

Answer:

Hello,

The function Approximate Tendon Losses is a simplified way of calculating tendon prestress loss when we don't run construction stage analysis. When we do run CS analysis, this is not needed, and all tendon losses are accounted for - immediate and long term. In your model you do have construction stages so you do not need the Approximate Tendon Losses analysis activated.

If you define the relaxation and the time dependent effects - creep and shrinkage, to Eurocode, then all effects will be calculated to the Eurocode definition. Note that while the relaxation losses are based on a code definition, the creep and shrinkage losses are an analytical result based on the strain changes which the creep and shrinkage effects in the structure have. So, in a way, the creep and shrinkage affect the tendon losses indirectly as per the Eurocode as long as the creep and shrinkage themselves have been defined to this code.

I hope this clarifies the topic. Let us know if there is anything else.

Kind regards,
Technical Support Team
MIDAS UK

Creation date: 12/13/2018 4:46 PM (MIDAS_UK_IM)      Updated: 12/14/2018 3:17 AM (MIDAS_UK_IM)
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approx tendon losses.png
time dependent control.png