relaxation coefficient in MIDAS tendon properties

Question:

Hi MIDAS Team,

I am having some problem in defining relaxation coefficient in MIDAS tendon properties area. What I do is that we have low relaxation strands (around 2.5%), therefore I define 2.5% on CEB-FIP 1978 and similarly 2.5% on CEB-FIP 1990. Both give different results. I think I am making a mistake as I believe that 2.5% is the correct value for CEB-FIB 1978 but in CEB-FIB 1990 I think I need to use some kind of ratio of 1000. Can you please help me quickly as Its urgent (models attached for 2.5% & 10%). Call me please at 050-8251420.

Thanks & Regards,

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Answer:

Hello,

In case of CEB-FIP 1990, you need to define the relaxation coefficient in accordance to the applied prestressing force.  It was noted that the yield strength was 1860MPa and applied stress was 1395MPa.  So, the ratio of applied stress is 0.75.  Judging from that, the relaxation could be taken at about 3% for 1000 hours from the image below.

Unfortunately, I do not have CEB-FIP 1978 easily available and hence won't be able to comment on relaxation loss value for that.  However, I don't believe CEB-FIP 1978 and 1990 loss values should match.  Kindly let us know why you think that these should match.

Regards,
Nandeep
Technical Manager, MIDAS