Hi all,
I have a doubt that I have already ask to the technical assistants, but I paste it here so it may help others too.
I have read the article ‘RM Bridge Elastic compression losses of tendons’… As it is said there, ‘Since RM2006 elastic compression losses are always considered automatically (formerly there was a check box “Elastic Comp. Losses included” in the Recalc-pad to select whether it should be considered or not).’
If I am not wrong, the actual force of the cable is controlled during the real process of stressing a tendon on site (post-tensioning), so the specified force controlledby the jack already takes into account the elastic losses that are produced during the stressing (the jack gives the ‘non-linear force’, already for the deformed shape of the tendon). Therefore, the elastic losses due to the current stressing shouldn’t be considered for that tendon (only for the other tendons previously installed).
Is RM considering elastic losses fof a cable due to its own stressing? Shouldn’t it be the other way? Is there a way to consider it properly?
Thanks!
I paste here the aswers I have received (quite fast, by the way) concerning this issue. It seems, as expected, that RM considers it correctly.
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De: Harald
Enviado el: viernes, 18 de octubre de 2013 14:20
Para: Rodriguez Molina, Rafael
Asunto: AW: dudas RM
Hi Rafael,
Regarding your doubts:
1. Elastic compression losses for tendons
Your understanding is correct and RM handles the initial stressing of a tendon as you describe below.
This (previous) recalc option refers to the effect of additional elastic shortening (e.g. by jacking another tendon in a later state) on the force distribution along the first tendon.
This is considered/done now automatically.
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Hi Harald,
Thank you very much for your response. I still don’t understand exactly what you mean with your response regarding tendon losses (I’m sorry, it’s probably not because your response is not clear but because of my misunderstanding, as English is not my mother tongue).
In my question I explained how I think it should be considered (RM should consider elastic losses of a cable due to every other forces BUT its own stressing), but I explained I didn’t know if RM performed that calculation correctly or if it considered those losses. With your response (“Your understanding is correct and RM handles the initial stressing of a tendon as you describe below”) I understand that for other forces the consideration is currently automatic, but it’s still not clear to me if:
a) RM handles it as it should be (without considering elastic losses due to its own stressing) or if
b) it actually considers elastic losses due to its own stressing (which is something we would have to know and accept even if it’s not exactly correct).
In case of b) (with I think is what you meant), is there a way to consider it properly? Is there a way to inform the developers about this so they may think about an improvement for next versions?
Thank you very much, and excuse me for insisting, but I want to be sure I have understood it 100%.
Best regards
Rafa
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Hi Rafa,
The correct answer is:
a) In case of post-tensioned tendons, tendon forces (as defined in ‘Stress’) are applied on the active structure/tendon and no elastic losses are considered for these tendons.
Hint: Elastic losses are only considered for ‘pre-tensioned tendons’. And consequent for such tendons stressing sequence is not simulated by action ‘Stress’ but is defined as nominal ‘PT-force’ in the tendon definition itself and is applied by action ‘PreTens’. Only in this case elastic losses from stressing sequence are considered in the tendon force distribution of the tensioned tendon…
Best regards,
Harald