'Encapsulated' post tension anchorages 1

[rkbarcant]

I would like peoples opinion on the term 'encapsulated' anchorage who are familiar with PTI's specifications, unbonded Post Tensioning slabs & also construction in 'agressive' areas such as coastal construction & parking garages.. This is specifically as regards construction in East Central Florida on the ocean/barrier islands..

Here is a link to PTI's page with an 'encapsulated' anchorage.. They may change this link, but I will try to describe it.

http://www.post-tensioning.org/recert_newdevelopments.asp

At the end anchorage the commonly used & locally supplied systems have an (epoxy or similar) coated area that has an 'end cap' (filled with grease). On the inside of the end anchorage there is a transition tube ~12/16" long that has a locking ring that connects the 'sleeve' (also referred to as a trumpet') to the anchor.. There is also a washer that the sheathing goes into as it enters the tube. According to PTI there should be 4" minimum embedment of the sheathing into the sleeve'.. The system is also supposed to be watertight to 3 foot head of water (~200 psf)..

PTI uses the words 'no voids'in their description of an 'encapsulated' system.. The way that I interpret that is that the 'sleeve' should be filled with grease (as indicated on the picture on their website).. This seems very logical when one considers that this system is to be used in an ‘aggressive’ environment and that the ends are an easy entry point for water borne chlorides and thus corrosion. In my opinion the ‘sleeve’ and whole end anchorage area should be at least as watertight and moisture resistant as the main sheathing. Rust requires the presence of air & water, & chlorides accelerate this process. I would like some independant interpretions of 'no voids'.. I have ordered the PTI spec on unbonded tendons, but do not have it on hand and will quote the full text when it arrives.. If anyone out there has access to it, please quote for me..

I am EOR and Threshold Engineer for a 4 story building beachside. What appeared on my jobsite, however, was not what was in the picture posted on PTI’s website as an ‘encapsulated’ anchorage.. The 'sleeve' was not 'filled' with grease & I could not see if the cable was completely coated with grease, and the void was actually 'filled' with (moist) air and there was visible condensation on the insides of the sleeve'. Additionally the 'locking rings were not in place and in a few locations the sleeve was not connected to the anchorage. The end caps were not translucent, but upon removal & inspection were filled with grease..

In addition, apparently during laying out of the cables, the sheathing was pulled away from the anchorage & sleeve and as much as 6" was fully exposed.. PS 'duct tape' wrap is not a legit fix - especially in anchorage areas. Water will leak..

The PT supplier said that I should have specified a 'fully encapsulated' system if I wanted the voids filled with grease.. PTI's technical Director said that there is also a 'propitiatory' system (not my supplier) that is 'fully encapsulated', but is it not of one of PTI's standard systems ('regular' & 'encapsulated') .. PTI's field/certification rep (?) and apparently the local Florida suppliers (or is it just our own) interprets that as not having a void in the grease surrounding the cable in the sleeve.. I beg to differ and would like other design engineers interpretations..

Thank god the contractor I am working for/with is going ahead & getting grease delivered to add in the field & fill the 'sleeves'. Hopefully it will not be a real mess, but I am sure there will be a lot of moaning & groaning by the workers.

I wonder if many of you have encountered the same condition that I have here.. One of the many disturbing things is that there may be a lot of buildings out there that have 'sleeves' that are not filled with grease but the EOR's think that they are.. I also thought that the PT industry was more regulated that it actually is.. Is this just in Florida or nationwide?

One of the lecturers at a seminar a few years ago said that PT anchorage problems were going to replace the asbestos fiasco of the 80’s & 90’s.. I now see what he meant..

 

[boffintech]

I am on a job right now where I am seeing the exact same problem that you have. I did not realize that there was a 'fully encapsulated' system versus an "encapsulated' system. I will have to check the specs after the holiday and verify the specific terminology.

It has been my experience that the real headache is getting the rodbusters to place the encapsulated tendons correctly with all the fittings fully engaged and snapped together. This is especially a hassle at construction joints where intermediate stressing occurs. As an inspector I’ve held many a meeting at CJs with EORs, owners, rodbusters and contractors where the contractors and rodbusters give long dissertations on why those things just won’t snap together.

 

[rkbarcant]

If the suppliers were truly delivering 'encapsulated' systems as indicated on PTI's website, I would not be concerned, but what they are delivering is, in my opinion, very prone to corrosion at the most vulnerable location.

PTI is a nationwide organization and should have a unifying standard, not one for engineers & one for contractors.. What the engineers read into the standards & specify, the suppliers & contractors should install. The suppliers seem to have 'interpreted' the standard to own their ends.. In addition, the standards for Florida should be the same as everywhere else.

I too am experiencing difficulty with the lackadaisical attitude by rodbusters & others not taking the time & care that they should, especially with the anchorage ends.. With the litigious nature of structural engineering nowadays, the only ones finally responsible are the EOR & inspectors – & the trades will just go on doing it ‘the way they have for the last 20 years’ without even knowing the trouble that they caused..

I am frankly disgusted with the overall quality of field labor and the 'blow & go' attitudes of contractors & subs all around.. The "I've been doing this way for the last 20 years" excuse.. I can partly attribute to the overall construction boom and rebuilding effort from last years hurricanes in the area - Any help is hard to find, far less good help.. If you give anyone too much grief, they will just go & work on other jobs where the inspectors are easier on them (fine by me, but not by the GC).. Sorry for the ranting...

 

[henri2]

rkbarcant, I do not know that much about cast-in-place USST post-tensioned construction but I do have the reference that you have ordered....so I'll try an provide some info requested and also pose some questions if you do not mind.

1. The 2000 edition of the PTI spec for USST defines encapsulated system in Sec 1.2 as follows: "A tendon that is completely enclosed in a watertight covering from end to end, including a protective cap over the tendon tail at each end. The encapsulation shall be as free of voids as possible and shall inhibit corrosion of all tendon elements".

2. As you can see, the definition does not use terms like "fully encapsulated" and or "regular encapsulated", albeit I have heard the terminology used.

3. The commentary C1.2 states that "some small bubbles and air spaces are normal and unavoidable in the fabrication and assembly process and shall not be considered as "voids" in the context of this defintion.

4. Sec 2.2.6.2 deals with Encapsulated Systems. In the first paragraph it states that " Encapsulation sytems using ''tape'' as a component are acceptable provided they pass all requirements of the hydrostatic water test and the requirements of Section 3.2.5.2". For repairs also check the companion publication Field Procedures Manual for USST, Appendix 11.6. Clearly duct tape is not what they had in mind.

5. For more on void-free criteria check Sec 2.2.6.2 item E and commentary C2.2.6.2

6. According to ACI 318-99 Section 18.16.4 USST corrosion protection must comply with PTI Spec for USST. However, in ACI 318-02 compliance is now per ACI 423.6. IBC-03 has the 2002 edition of ACI 318 as a referenced standard while IBC-00 has the 1999 edition. Is ACI 423.6 that different from PTI's USST spec?

7. In the PTI link you provided, two encapsulated systems are shown; the translucent sleeve filled with P-T coating and the "no-void" rubber sleeve. Which of the two is more commonly used and which is easier to fabricate?

8. Are the P-T plant and P-T field personnel on the project certified by PTI?

 

[rkbarcant]

1), 3) & 4) PTI's Tech Director read off over the phone but I didn’t get all of it. I do not have a hard copy of it but I went ahead & ordered them (also joined PTI to met member discounts).
2) Apparently 'fully encapsulated' is a term that PT suppliers locally in Florida use - Seems like an an 'excuse' for an 'extra' in my eyes & very myopic in my opinion opening themselves up for litigation (a lot of the buildings are condos).. People will use PT regardless of the small additional cost for 'encapsulated' (~5% more) because of span & floor/floor height issues.. This will only give PT, as an industry, a bad rep and that PTI should be all over this issue.. PTI only has 'regular' and 'encapsulated' defined in their normal spec's..
5) Don't think he read me these..
6) I don't have a copy of ACI 423.6 so can't compare. In Florida we use 2005 FBC, not IBC.
7) The supplier sent the top 'encapsulated' system, but with a few critical differences.. Sheathing not filled with grease.. Non translucent end caps (but these were grease filled).. Many other 'shop problems' like most loose ‘locking rings’ are out of place, sloppy cutting of sheathing etc etc..
8) PT Plant is PTI certified and a major Florida supplier.. However, the installers are another story.. I haven't asked, but I would bet that the answer is no.. They have apparently been installing PT for a while on multiple beachside condos, but in my book that says nothing (good) as they are set in the way they have been accustomed to doing business and resist change. As I mentioned earlier, we have a major labor problem over here.. The GC is running scared since the original rodbusters (who did the foundation) have already left.. Too much easy $ work around to deal with picky inspectors..

 

[henri2]

Continuing with follow-up comments...

Item 6. I noticed from the FL Bldg Code website that the current FL Bldg code utilizes IBC-03 as the base code. Chapter 19 of the FL Bldg Code is for the most part based on ACI 318-02 with some modifications and additions...no? If there is no modification to ACI 318 Section 18.16.4 in chapter 19 of the FL bldg code then ACI 423.6 kicks in as a code minimum requirement instead of PTI's spec on USST.

Item 7. Have you observed this installation problem on other projects? Boffintech has pointed out similar problems he has observed in the field. Perhaps the difficulty in assembly is due to design of hardware....and is not an issue addressed in evaluation reports.

In the penultimate paragraph of your first post in this thread you wrote "I also thought that the PT industry was more regulated that it actually is.. Is this just in Florida or nationwide?". In my opinion, in areas where building departments inter-alia are large enough (and adequately funded) to have a division that enforces/oversees special inspection and structural observation provisions of the code, compliance with approved plans and specs is enhanced. Do bldg depts in FL typically have a division which focuses on threshold inspection?

In the last paragraph of your first post you conclude by stating "One of the lecturers at a seminar a few years ago said that PT anchorage problems were going to replace the asbestos fiasco of the 80’s & 90’s.. I now see what he meant..". Interesting you should bring that up; not too long ago I had read that strands in high-rise post-tensioned concrete condos built in the 70s and 80s in Calgary developed serious corrosion related problems...and as a result the use of post-tensioned concrete for residential construction waned. So you are right when you suggest that PTI should get more involved to mitigate this scenario...but so too should other major players who have a stake.

 

[boffintech]

Anyone who can work "penultimate" into a post gets a star in my book.

BTW, you don't have to look far for an anchorage failure that resulted in structural failure; remember that pedestrian bridge at Lowes International Speedway that collapsed? And that bridge was factory pre-cast where quality control is supposedly the highest.

Also, it has been my experience that the difficulty in assembly is NOT due to design of hardware but due to the lack of effort of labor. At CJs where intermediate stressing occurs and at stressing ends of tendons the cast-in-place hardware must be sufficiently cleaned so that the pieces snap together. This takes time, time is money, you see where this going.

Similar to rkbarcant's problem, on my current job the sheathing does not enter into the encapsulation tube at the at the anchorage ends. At the factory the sheathing is simply not being cut off properly; it’s too short. The factory claims that they will now correct this and the field labor is using water proof tape to seal these up. This seems to make the EOR happy.

 

[rkbarcant]

First off guys & (gals?), thanks for all of the past & any future responses to this post

Correction; The applicable Code is 04’ FBC (not ’05).. The suppliers are using PTI’s as a basis.. I have not got a copy of ACI 423.6 to compare.. I hope they are not too much different.. None the less the intent is what is getting my goose here.. It’s ridiculous to provide a system where the critical ends are surrounded by (moist) air & will let salt water into it sooner or later.. It’s not like these guys don’t know where this is being built..

The filling (or not filling) of the sleeves seems to be a shop problem, although with the crappy job they did of securing the sleeves to the anchorages with the locking rings, I see a big greasy mess in the making – not to mention the occasional split sleeves..

The suppliers will fill the sleeves with grease if you ask for ’fully encapsulated’ tendons, but my point is that they should do that regardless since an ’encapsulated’ tendon should be filled with grease, at least the way I read the specification.. What I was looking for was other engineer’s opinions (not contractors who want to cut corners at every opportunity). My ‘Florida or Nationwide’ comment, was to see if ‘encapsulated’ in Oregon (for example) meant ‘substantially filled with grease with no voids’, or if one needed to specify ‘fully encapsulated’ there also. Are the suppliers & engineers using the same terminology consistently? The whole idea of a National governing body (such as PTI), is that an engineer in Oregon should be able to specify work in Florida, & vice versa, and get the same product on site..

I have also seen damage on PT condos on the beach (1985 vintage - I did not do the original design) that were as a result of excessive concrete cracks (double cantilevered balconies), poor concrete (probably excessive water added on site), damaged sheathing & anchorages etc.. In some areas ~75% of the cables broke (with ‘slab popouts’ etc) and the whole area needed shoring.

In Florida the building departments are typically small & do not have inspectors experienced enough to deal with these types of problems. In ~1984 after the collapse of Harbor Key condos (under construction, 10+ lives lost, progressive collapse of one slab onto another etc) ‘threshold inspectors’ came into being.. To get to be a TI you have to have proven experience designing & inspecting 4+ story, + high occupancy buildings etc. The concept is that we work for, & finally report to the building department but are paid by the owners.. As a matter of interest, the Harbor Key site is about 2 blocks away from this site!

Boffintech, I agree that a large part of the problem is a labor one, the blow & go attitude exists in the shop & in the field.. Time = $..

If they can get you to buy off on anything & take the ‘rap’, they will.. A non state registered engineer or workman will not get called to court in the event of a problem.. They are only interested in registered engineers, threshold inspectors, architects and contractors.. All others go free..

Boffintech , Henri2 & all others out there…As a ‘poll’
- What geographical areas do you all work in?
- Do you see the sleeves ‘filled with grease with substantially no voids’?
- Did/do you specify ’fully encapsulated’ or ’encapsulated’ tendons?

 

[boffintech]

Boffintech , Henri2 & all others out there…As a ‘poll’
- What geographical areas do you all work in?

Atlanta, GA

- Do you see the sleeves ‘filled with grease with substantially no voids’?

Have only seen encapsulated tendons called for on parking decks.

Have never seen sleeves ‘filled with grease with substantially no voids’

- Did/do you specify ’fully encapsulated’ or ’encapsulated’ tendons?

Have never heard the phrase ’fully encapsulated’.

 

[rkbarcant]

Boffintech

It seems like you are getting ‘substantially filled with air’ like I am, even though ‘encapsulated’ is what was specified..

I talked to a friend in Ohio & he said he did a parking garage a couple of years ago & that the 'encapsulated' tendons were ‘substantially filled with grease’. He never heard the term 'fully encapsulated'.

I also spoke to someone in Orlando who works at a real big company & their standard is ‘encapsulated’ & they think that ‘substantially filled with grease’ is what they should be getting, but are checking with other engineers in the company & their field guys..

 

[Zambo]

I am used to working with bonded post tensioned structures. In this case we have a limited period in the specification in which to grout the ducts - generally within 3 days. If this time period is not feasible we must provide a corrosion inhibitor. For external post tensioned systems there are different requirements.

What I don't understand is how it can be possible for a contractor to propose an unbonded internal post tension system without an effective corrosion protection system.

What are the cost implications of pproviding either galvanised wire or HDPE coated strand to at least provide some corrosion resistance to PT strands which appear to be completely unprotected.

 

[rkbarcant]

I am not familiar with ‘bonded’ systems and they seem to be used in larger more ‘significant’ structures such as bridges etc.

I agree fully that the un-bonded systems out there should be provided by all PT suppliers should be protected from corrosion. The GC’s themselves are not PT savvy – it is too much of a ‘specialty’ item for them to get that intimately involved in.

In my case we will attempting to fill the ‘sleeves’ with grease next week so I will post later how that went - but I am pretty sure that there will be moaning groaning & cussing involved – not to mention a greasy mess..

At the stressing end the sleeve will be field placed. I do not have the PTI ‘Field Procedures Manual for Unbonded PT Single Strand Tendons’ (again ‘on order’) & am hoping that it specifically covers how the sleeves at the stressing end should be filled with grease, but we should probably follow a similar procedure for filling the fixed ends. If anyone out there has this handy, see if they even specifically address this issue. I am going to need it in a few days when the ‘field repairs’ start.

The other overall ‘issue’ is the interpretation by field personnel of ‘fixes’. They tend to choose easy short cuts to make it ‘look good’ for the casual inspector, but upon close scrutiny lots of ‘cracks’ emerge.

I was on site yesterday & took a closer look at the anchorages, and there is a ~1/8” annular gap where the sheathing enters the sleeve. I was hoping that this would be a tight sleeve that would not allow water in & also keep the grease from getting out. It looks like taping will be the only option, but because of the difference in diameters (5/8” for the sheathing & 1” for the sleeve) taping may not be effective for watertightness.

As far as cost implication & changing to galvanized or HDPE coated, I doubt it would happen – the industry seems too fixed in it’s ways and resists any change, however ‘small’. To get them to fill the sleeves with grease is like pulling teeth - & it’s in PTI’s standard spec’s. Even so, I would be concerned about the galvanizing been scraped off into the wedge area, the effectiveness of the ‘wedge’ grip’ due to soft galvanizing, possible embrittlement since 270 ksi steel. If using a HDPE coating, you would need to scrape it off at least 6’ at the ends to allow seating wedges etc. I believe that when only a ‘small’ area is ‘exposed’ (by local scraping off of galvanizing for example) it would tend to be a concentrated corrosion point & cause even more rapid deterioration of the cable system..

FYI; A link to PTI’s ‘tape’ field repairs..

http://www.post-tensioning.org/pdfs/research-update-dec-2002.pdf

Again, thank you all for your interest, input & efforts.