I think this value of ecu is maximum.

i totally agree with abbas that the ecu is maximum

This pdf file may be helpful

https://pdfs.semanticscholar.org/bb7f/30771274747aef316ae53fb1fb8112f544a1.pdf

Thanks a lot dear Mohannad Husain, your pdf was very useful indeed but there was no answer to my question.

It is clearly mentioned in ACI 440 that when the confined strain in compression concrete exceeds 0.01, the concrete will loss integrity due to excessive cracking due to compression not tension. That is mean failure is reached.

Dear Nazar K Ali you are right, but I want to know, in design procedure, when do we get that we can not increase our member's compressive strength anymore and FRP with maximum number of plies is not a suitable method for strengthening?

Dear Mohamad..further beyond the answer of dr. Nazar..we have a lot of strengthening project due to the aging of structure or explosion or erosion,,, and all of these projects prove that the FRP a very suitable method for strengthening

Of course dear Amjad but strengthening by FRP has its own limits, I mean you can not increase a member's compressive strength to infinite, there is actually a limit, and that limit determines the restrictions of using FRP.

for example maybe excessive loading of a member after construction can not be compensated by FRP at all (with any number of plies).

Dear Mohamad Maldar · 

If FRP are used to wrap an axial member. then the is indirect increase in axial load capacity due to confinement effect.

Best regards

Dear Mohamad Maldar

For sure you can not increase a member's compressive strength to infinite because failure can be assign when any component of a structure failed. In your case the failure of concrete brought the failure to the whole system while FRP is still not reached the ultimate stress.

yes dr nazar you are right..you can check the attached research paper

Thank you Dr. Amjad

Thank you all doctors for your answers.

I would be appreciated if anyone could answer more specific and relevant to my question. Thanks.

Failure as I mentioned attains when one component failed to sustain the load. That is mean it is not suitable to use ultra high strength material, (second material), if the other material (the first) can not continue working with it.

Dear Mohammed, thanks for your answer.