EXTERNAL POST-TENSIONING

[eljineer]

Hi,

I'm a newbie here in this forum.
Is anyone here can discuss how to calculate/design the external post tensioning with harped tendon for the retrofitting?
Thank you.

 

[TehMightyEngineer]

That's quite a topic; I'd suggest narrowing it down.

What specifically are you looking at learning?

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[rapt]

Have you studied and practised PT design in detail and know how to analyse and design for it by manual calculation (not using automated software tools?

If not, I would suggest starting there.

Otherwise I would hire someone who can!

 

[eljineer]

hi rapt,

I've practiced and studied PT design (internal only) that started this last 2 months only with the help of many guidelines and references.
I can analyse it by manual calculation too. Actually I will design 2000 plus PT Girders/Beams that need to be finished at the end of Nov this year with the help of ADAPT Builder/PT.

I seek for help in some experts (like you) for the external post-tensioning because there is no specific guidelines or limited on this retrofitting method,
all i have is my concept that i learned in PT (internal) only and need to finished my design for 1week only. Sorry, you can hire whoever you want. No need to be rude.

 

[eljineer]

Hi TehMightyEngineer,

Thank you for your response. I want to verify some points on external post-tensioning.

1. Is allowable stresses in internal PT is same to the external PT?
2. Draped/parabolic tendon produce an uniform uplift in the member. For the harped tendon for the external pt
produce upward load through deviation device only?(obviously) So can i analyse it like a simple analysis with additional upward load only?
3. If i use steel element for the anchorage device there is no pre-compression in the member. What if i will anchor the tendon in the existing slab,
do i need to check also the slab?
4. Do you have any good reference in external post-tensioning?

I appreciated very much for your help.

Best regards.

 

[Ingenuity]

eljineer:

This technical report entitled EXTERNAL POST-TENSIONING by VSL is a starting point: Link

It is a little dated (1992), but still relevant. Several of the authors (notably Marti, Ganz and Matt) are a mix of experienced practitioners and researchers.

 

[eljineer]

Ingenuity,

Appreciated. Thank you very much.

 

[rapt]

eljineer

I am not being rude. If you fully understand and can apply PT design logic by manual calculation, then you will be able to do external without any problems. Any differences you will understand and be able to apply in your calculations.

If you have read a couple of general texts on PT and have only ever designed using automated PT software (and by the sound of it, only for a couple of months), then you will probably need to get more understanding of basic PT principles and their application before attempting it.

You do not need any specialised books on external PT. Just a very good understanding of PT in general from good text books (avoid most modern American/PTI texts), and that took me and a lot of other very experienced PT designers a lot longer than 2 months (without touching design software) to get!

 

[eljineer]

rapt,

Yah.. I really admire the innovative engineers that develop the PT system even it is not prescribed on the codes on that time.. But now, we lived in the world with technology and advancement. If you will do a detailed design of hundreds or thousands of structural elements with just hand calculation with a limited time, I will say that you are not a good engineer. Just take the advantages of any softwares. Also remember that any software is just a tool that will give your desired results. Don't let the software control you. I'm 100% sure that if you dont understand the basic concepts and principles on PT system you will have a very hard time to design PT in software.. Remember, garbage in. - garbage OUT!

 

[rapt]

I never said not to use software. Just to have sufficient experience in the topic before you do.

But how do you decide which of "any software" you are using is suitable for you and what you are trying to do. Or even if it is doing things correctly in all situations. There is always a disclaimer at the start saying the software designer takes no responsibility for what you do with the software. Is it sufficient to read brochures and catalogues!

And when you are trying to manipulate the software to do something out of the ordinary, how do you know what the effects of doing different things in the software will be.

 

[eljineer]

rapt,

Thanks for all your comments even though you didn't help or share any good idea regarding to the above subject. Maybe you are just a type of person that want to keep ideas/experience to himself. Anyway I already know how to analyze/design External PT for retrofitting. And like you, I have experience now regarding to this topic.

Keep safe and God Bless.

-engr. eljin