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HDPE duct in PT structure EC2
2

HDPE duct in PT structure EC2

HDPE duct in PT structure EC2

(OP)
Hi,
Do you guys know why EC2 clause 7.3.1 requires PT structures under XC3 to be under decompression under quasi-permanent load? My interpretation is to prevent corrosion of strands. And my question is if we are using plastic HDPE duct, do I still need to check for decompression? If no, is there any specific tests or requirements (e.g durability test, chemical composition etc..) for HDPE duct to be eligible to use without complying EC2 decompression requirement. I did send my queries to CEN and EOTA yesterday so far no reply yet so ... Hope you guys can help me out like you always did :).



Even in TR43 mentioned that plastic duct should be used for external environment but does not mention the type of duct. Does it mean any plastic duct will do?



Thanks

RE: HDPE duct in PT structure EC2

You would be very hopeful if you think you are going to get an answer from CEN!

The EC2 requirements are weird and very inconsistent.

They treat "fully encapsulated" unbonded PT the same as RC while being extremely strict on bonded PT, to the point of being unworkable. Even though most of the long term problems with PT around the world are in unbounded PT buildings due to poor material selection and construction practices with the strand protection resulting in "encapsulation" not working properly.

My understanding is that the Germans on the committee were still worried about hydrogen embrittlement from the Munich Music Hall collapse many years ago and forced these rules. Even though the problems on that building were specific to the building and the materials etc used. I would have thought that the experience around the world with bonded PT in buildings over the last 50 years would have convinced them otherwise, but it obviously did not.

In my experience, the decompression requirement should only be required for extreme environments.


RE: HDPE duct in PT structure EC2

(OP)
Hi RAPT,

Glad to have your reply.

Quote:

being extremely strict on bonded PT, to the point of being unworkable.
Yes that is the problem. A lot of people here do not care WHY. They only care what is in the code. Worse case! imagine a warehouse design where we have to consider about 80% of L.L as sustained load, it would kill us.

That is the reason why I am looking for alternative. BTW any comment on plastic HDPE duct?

Thanks

RE: HDPE duct in PT structure EC2

I have been pointing this out to users of EC2 for many years, as well as to people on the CEN committees.

Most designers I know simply ignore the requirement except in extreme environments.

Just think, every PT building built in Singapore for the last 45 years (I think the first was in the mid 1970's. I designed several there in the late 1970's and all were class 3 to BS8110) would fail this check. How many of them are having problems with corrosion of bonded PT tendons? How many have required repairs to bonded PT tendons. None would be my guess.

Even all of the class 2 designs to BS8110 would fail this check. And for how long have I been fighting people in Singapore to get them to forget class 2 and design partial prestress (class 3) to get the benefits of the extra cost savings by not wasting extra prestressing and concrete in trying to achieve class 2 or even class 1. You have been to at least 3 of my design courses there and know I go into it in detail every time.

These requirements are not even realistically achievable in a parking structure let alone a warehouse.

Most plastic duct I have heard of has been used for multi-strand tendons.

VSL USA (when they existed in the 1990's) tried a plastic 2 strand bonded system but as I understand it, that suffered a very quick death as it was too expensive.

I would work on Singapore Standards Association to get them to over-ride the EC2 rule. The prestress industry there should get together and get it changed

RE: HDPE duct in PT structure EC2

Quote (rapt)

Most plastic duct I have heard of has been used for multi-strand tendons.

VSL USA (when they existed in the 1990's) tried a plastic 2 strand bonded system but as I understand it, that suffered a very quick death as it was too expensive.

Flat HDPE ducting is readily available today in the US - predominate use is "other than buildings".



Source: Link

VSL's US 2-strand bonded system still exists - VSLAB - and was originally marketed to shorter span one-way slabs to parking structures (with 60' span PT beams) in aggressive environments. Although still available today, I don't believe it is very popular.

RE: HDPE duct in PT structure EC2

(OP)
Hi Ingenuity,

Thanks so much for the link and for coming here to reply.

Hi Rapt,

Quote:

Most designers I know simply ignore the requirement except in extreme environments.

Haha. Yes, that's what I have been doing so far. I am just preparing for the sudden surprise from authorities. The risk is just simply too high.

Quote:

not wasting extra prestressing and concrete in trying to achieve class 2 or even class 1. You have been to at least 3 of my design courses there and know I go into it in detail every time.

It is really and always sad to see all the money casted inside concrete. I would love to attend 4th time if I could :). Everytime I attend your course, I can learn new things.

Quote:

I would work on Singapore Standards Association to get them to over-ride the EC2 rule. The prestress industry there should get together and get it changed

I would love to see that happen but as you know to get together is not simple as that.


RE: HDPE duct in PT structure EC2

I will talk to a few of your opposition and see where they stand.

RE: HDPE duct in PT structure EC2

(OP)
Thanks rapt

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