5 Unexpected Advantages of Post-Tensioning

Since the 1950s, post-tensioning concrete has grown in popularity. Whether you’re trying to streamline the building process, reduce costs or give a structure the best chance of surviving weather hazards, there are numerous benefits of post-tension slabs.

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Here’s a look at some hidden advantages of post-tensioning concrete and why you should consider these methods for new structures.

What Is Post-Tensioning?

Post-tensioning concrete is the process of adding steel bars (tendons) below a mixture’s surface. Once the concrete fully cures, tension is applied to the steel bars. These reinforcements introduce stress to the concrete, which can prevent cracks and shifting down the road.

Construction teams rely on post-tensioning methods to help concrete reach its strongest state. This process is efficient for creating surfaces that can withstand the loads required for a newly developed structure.

Benefits of Post-Tensioning

Consider these surprising advantages of post-tensioning.

1. Saving on Costs and Materials

Prestressed concrete supports larger loads compared to traditional pouring. Using post-tension methods means concrete substrates are thinner, sometimes by as much as 20%.

When a building is complete, the total height of the structure is shorter than constructing slabs without post-tension reinforcements. Smaller buildings call for teams to use less cladding, concrete, cement and shear. Extra materials can be used for future projects or returned to the manufacturer to increase your bottom line. Either way, you’ll save on costs and materials.

2. A Sustainable Approach to Building

When you rely on post-tensioning concrete methods, fewer materials are involved in the final structure. This includes the amount of cement used to create concrete mixtures — a significant source of carbon emissions.

It’s possible the timeline for a building project will be shorter with post-tensioning concrete, which lessens the amount of time gas-powered tools and vehicles run from the start of the assignment through completion.

3. Efficient Construction Timelines

The setup for post-tension procedures can be done quickly without the variables of traditional curing. The fact that crews spend less time laying steel supports means teams will be ready to pour mixtures and let the concrete dry on an impressive timeline. Your post-tension building project can progress consistently.

4. Crack Control

Post-tensioning results in compressive stress in concrete, which helps to reduce the effects of shrinkage and temperature changes that can cause cracking. The post-tensioning system consists of steel strands that are tensioned after the concrete has hardened, creating internal forces that resist external loads.

Post-tensioning systems are effective for crack control because the tendons act as reinforcement for the concrete and prevent it from splitting apart. The tendons are anchored at both ends of the concrete member and are usually placed in ducts or sleeves to allow them to move freely during tensioning.

The tendons are tensioned by hydraulic jacks and then locked in place by wedges or nuts at the anchorages. The tension in the tendons induces a compressive stress in the concrete, which counteracts the tensile stress caused by shrinkage or bending. This way, the concrete remains relatively crack-free and watertight throughout its service life.

5. Better Performance

Many property owners building post-tension structures find surfaces do a fantastic job of limiting unwanted vibration and sag. Inside the poured concrete, cables help to balance the load.

Rather than the center of slabs being put under immense stress where they can crack, the internal cables take care of the heavy lifting. Over time, concrete maintains its shape and refrains from dipping downward when objects are placed on top of it.

About Post-Tensioning Products and Services From STRUCTURAL TECHNOLOGIES

STRUCTURAL TECHNOLOGIES provides VSL post-tensioning products as well as construction systems in the United States. Whether you want to build or repair a commercial building, parking lot or similar structure, we will assist with design, installation and material fabrication for unbonded monostrand post-tension systems, bonded multistrand post-tension systems, shear reinforcements, barrier cables and lockable dowels.

We specialize in external and internal post-tensioning technology. STRUCTURAL TECHNOLOGIES provides you with solutions for installations outside a structural element — within grouted ducts — or within an existing member — via core drilling — to handle the scope of your project.

Get Started With Post-Tensioning Today

To learn more about post-tensioning products and our service capabilities, submit a contact form with STRUCTURAL TECHNOLOGIES.

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Post-Tensioning Software

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Post-Tensioning Software

Post-Tensioning Software

ajk1

(Structural)

(OP)

25 May 17 00:14

What is the best software available today to use for post-tensioning, particularly as it relates to checking existing post-tensioned beams with unbonded tendons and bonded rebar? We want to determine the utilization ratio (Factored Moment / Resisting moment) when tendons break due (due to corrosion). We are checking to the Canadian CSA A23.3 Standard.

We have been using ADAPT PT but are looking to see what else is out there, and how people have found it. Some software that I have heard about is "SAFE" but the post-tensioning module is relatively expensive, (and I am not sure that it gives the utilization ratio) and RAM CONCEPT and perhaps SAFE has a p.t. module.

I am looking for something that is bug-free, or that if we find a bug the software marketer will not require us to pay for the next edition of the software in order to get the bug fixed.

RE: Post-Tensioning Software

KootK

(Structural)

25 May 17 00:20
Ram ConcePT
Safe
Adapt
Posten X (may be US only)
Concise beam (simple spans)

In most cases, I suspect that you're utilization ratio may be something that you have to massage into being yourself based on the output of the software. Ultimate moment capacity of PT systems isn't all that difficult to calculate by hand really.

RaptRam ConcePTSafeAdaptPosten X (may be US only)Concise beam (simple spans)In most cases, I suspect that you're utilization ratio may be something that you have to massage into being yourself based on the output of the software. Ultimate moment capacity of PT systems isn't all that difficult to calculate by hand really.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Post-Tensioning Software

Ingenuity

(Structural)

25 May 17 07:27

Quote (ajk1)

What is the best software available today to use for post-tensioning, particularly as it relates to checking existing post-tensioned beams with unbonded tendons and bonded rebar?

"Best" will be a bit subjective, so take the following as 'my opinion' only.

I use RAPT, and have for over 20 years. I have also used ADAPT 2D and CONCEPT (FEM 3D when it was by the original author/s), and in-house software from a multi-national PT company too.

The majority of PT work I do these days is related to existing UNbonded PT structures to ACI 318 where we check the as-designed/as-built condition and from that base-model then run several "what-if" cases considering corroded/severed tendons. Then during actual field investigations (invasive probes, lift-off testing, etc) we adjust/tweek the PT to reflect the current (or projected future) level of non-corroded/non-severed tendons. It appears my application is similar to yours.

For this type of application, the software cannot be a black-box design tool - you want full user-control, in my opinion - coupled with an experienced PT engineer. The software needs to allow the user to input the actual number of tendons, the actual CJ locations for intermediate stressing, the dead-ends, the live-ends, the drape high and low points, harped or parabolic profiles etc. It should enable you to accurately model RC pour strips, setdowns, step-ups etc.

Additionally, the software should allow the user to be able to input USER-defined rebar with bar diameter, quantity and length, so upon running the software it uses this defined rebar when it is checking initial strength, stresses, cracked section analysis etc.

However, similar to what KootK was suggesting, most design software will "add" rebar to meet any strength deficiencies, so the software will provide "design" capacities so your 'utilization' (C/D) factor is >=1. The software should be calculating flexural capacities, for example, BEFORE and AFTER it adds rebar over the USER-defined rebar, so that makes checking the C/D ratios easier, and I usually just use a spreadsheet to check C/D ratios for different runs, based upon the capacities from the software.

Often with older PT structures with corroded tendons there are also other defects, like excessive flexural cracking and deflections. The software should also be capable of undertaking cracked-section analysis, and allow user-defined creep and shrinkage data to estimate long-term deflections.

RAPT ticks all the boxes for my specific applications.

"Best" will be a bit subjective, so take the following as 'my opinion' only.I use RAPT, and have for over 20 years. I have also used ADAPT 2D and CONCEPT (FEM 3D when it was by the original author/s), and in-house software from a multi-national PT company too.The majority of PT work I do these days is related to existing UNbonded PT structures to ACI 318 where we check the as-designed/as-built condition and from that base-model then run several "what-if" cases considering corroded/severed tendons. Then during actual field investigations (invasive probes, lift-off testing, etc) we adjust/tweek the PT to reflect the current (or projected future) level of non-corroded/non-severed tendons. It appears my application is similar to yours.For this type of application, the software cannot be a black-box design tool - you want full user-control, in my opinion - coupled with an experienced PT engineer. The software needs to allow the user to input the actual number of tendons, the actual CJ locations for intermediate stressing, the dead-ends, the live-ends, the drape high and low points, harped or parabolic profiles etc. It should enable you to accurately model RC pour strips, setdowns, step-ups etc.Additionally, the software should allow the user to be able to input USER-defined rebar with bar diameter, quantity and length, so upon running the software it uses this defined rebar when it is checking initial strength, stresses, cracked section analysis etc.However, similar to whatwas suggesting, most design software will "add" rebar to meet any strength deficiencies, so the software will provide "design" capacities so your 'utilization' (C/D) factor is >=1. The software should be calculating flexural capacities, for example, BEFORE and AFTER it adds rebar over the USER-defined rebar, so that makes checking the C/D ratios easier, and I usually just use a spreadsheet to check C/D ratios for different runs, based upon the capacities from the software.Often with older PT structures with corroded tendons there are also other defects, like excessive flexural cracking and deflections. The software should also be capable of undertaking cracked-section analysis, and allow user-defined creep and shrinkage data to estimate long-term deflections.RAPT ticks all the boxes for my specific applications.

RE: Post-Tensioning Software

ajk1

(Structural)

(OP)

25 May 17 12:22

To Kootk -

Thank you for the list. That is excellent and exactly what I was seeking. I suspected that you would respond. I rely on you!

Is the order that you have listed them representative of your opinion of their ranking, with best at top of list, or does the order have no significance?

Are you familiar with all of them, and if so, would you hazard some comments on the pros and cons of those with which you are familiar?

I used POSTEN about 30 years ago. I usect it must have changed a lot since then.

I have used ADAPT PT for a long time but am looking around for something else now.


To Ingenuity:

Sounds like you are doing quite similar investigations to what we are doing. That is an excellent summary of the important parameters. Thank you for taking the time to put it together.

We generally have not run into significant cracking issues, or any deflection issues, although that could certainly happen.

Are you generally using the ACI 318 Code or the CSA A23.3 Standard? Although the CSA Standard is a better fit to the empirical data for determining the pr stress in the tendons, it is more awkward to use. I do have a spreadsheet that I wrote that checks the resisting moment at centre and ends of a span, and that spreadsheet also gives the c/d ratios, but c/d ratio is not generally a problem (nor would it be expected to be, if the beam was originally designed correctly). I don't get too hung up about service load stresses when checking existing beams with corrosion broken tendons. My main concern is its safety.

How do you find the ease of inputting the existing rebar? I find it awkward in ADAPT because it defines the position of the ends of the bars always from the left support, rather than from the support over which the bar is located. How does RAPT define the rebar ends.

Does RAPT include Canadian hard metric bar sizes (which differ from the American soft metric bars)?

Thanks again for your help. Much appreciated.

RE: Post-Tensioning Software

slickdeals

(Structural)

25 May 17 12:30

From a point of inputting existing reinforcement and checking existing slabs, I think RAM Concept has to be right up there as your pick. As with any software, you should realize what it's limitations are and what hand-checks need to be done to get to a comfort level. I would highly recommend RAM Concept over SAFE or ADAPT. I haven't had an opportunity to use RAPT but obviously have heard good things about it as well.

RE: Post-Tensioning Software

KootK

(Structural)

25 May 17 15:30

Quote (ajk1)

Is the order that you have listed them representative of your opinion of their ranking, with best at top of list, or does the order have no significance?

No significance whatsoever.

Quote (ajk1)

Are you familiar with all of them, and if so, would you hazard some comments on the pros and cons of those with which you are familiar?

I'm familiar with all of them in the context of new design but I've only used a couple as you intend to. Truly, I defer to Ingenuity's thoughtful comments. That said, I'll do what I can. I'm going to assume that, regardless of the software, this is something that you plan to do in 2D strip mode rather than 3D FEM.

Rapt. Good blend of features and transparency. Free demo version too if I'm not mistaken.

Ram ConcePT. This is my goto for new construction and, as slick mentioned, it's pretty powerful for as-buit as well. The drawbacks, as I see them, are cost, licensing headaches, and the fact that this is work that I would normally attempt in 2D. ConcePT can absolutely be run in strips but it's not really built for that.

Safe. It's good software similar to ConcePT. At the risk of sounding like a jerk, however, I can't think of a single way in which it is superior to any other package other than the fact that it can integrate with ETABS.

Adapt. In 2D I'd consider it to be a weaker version of Rapt. I haven't tried out their 3D offering yet but it looks pretty powerful. You're looking to migrate away from Adapt so I'll leave it at that.

Posten X. Not much has changed I suspect. It's still 2D, very transparent, and relatively cheap. Particularly if you're not overly concerned with deflections, it might be an attractive alternative. I'd also consider this to be a weaker version of RAPT though so, for me, there would need to be cost advantages.

Concise beam. Unbeatable for cost, simplicity of use, transparency and reporting. It's even Canadian in origin. Unfortunately, it's purpose built for precast/prestressed. You'd have to fudge some things pretty heavily to attack multi-span unbonded problems and I suspect that would be a big disadvantage for your work.

I'm shocked that nobody's actually added anything to my list. I'd have thought that there would be more out there, especially non-north american stuff.

No significance whatsoever.I'm familiar with all of them in the context of new design but I've only used a couple as you intend to. Truly, I defer to Ingenuity's thoughtful comments. That said, I'll do what I can. I'm going to assume that, regardless of the software, this is something that you plan to do in 2D strip mode rather than 3D FEM.Rapt. Good blend of features and transparency. Free demo version too if I'm not mistaken.Ram ConcePT. This is my goto for new construction and, as slick mentioned, it's pretty powerful for as-buit as well. The drawbacks, as I see them, are cost, licensing headaches, and the fact that this is work that I would normally attempt in 2D. ConcePT can absolutely be run in strips but it's not really built for that.Safe. It's good software similar to ConcePT. At the risk of sounding like a jerk, however, I can't think of a single way in which it is superior to any other package other than the fact that it can integrate with ETABS.Adapt. In 2D I'd consider it to be a weaker version of Rapt. I haven't tried out their 3D offering yet but it looks pretty powerful. You're looking to migrate away from Adapt so I'll leave it at that.Posten X. Not much has changed I suspect. It's still 2D, very transparent, and relatively cheap. Particularly if you're not overly concerned with deflections, it might be an attractive alternative. I'd also consider this to be a weaker version of RAPT though so, for me, there would need to be cost advantages.Concise beam. Unbeatable for cost, simplicity of use, transparency and reporting. It's even Canadian in origin. Unfortunately, it's purpose built for precast/prestressed. You'd have to fudge some things pretty heavily to attack multi-span unbonded problems and I suspect that would be a big disadvantage for your work.I'm shocked that nobody's actually added anything to my list. I'd have thought that there would be more out there, especially non-north american stuff.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

If you want to learn more, please visit our website post tensioning system services.

Additional reading:
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RE: Post-Tensioning Software

SethGuthrie

(Civil/Environmental)

25 May 17 17:20

Let me know if you have any questions about Ram Concept specifically or need a demo.

RE: Post-Tensioning Software

ajk1
What is the purpose of a diamond blade?
What are the benefits of gold stainless steel sheet for packaging machines?

(Structural)

(OP)

25 May 17 17:28

To Slickdeals -

Inputting the rebar takes me more time than anything else in ADAPT, so ease of inputting existing rebar is a significant factor for me, and your comment on Ram ConcePT in this regard is useful.

To Kootk -

A nice concise summary. Thanks very much.
Seems like Rapt and Ram ConcePT might be the 2 programs to start looking into.
I suspect that neither program may calculate the utilization ratios at 20th points along the span as ADAPT does, but perhaps I can do that manually.


Have any of you found that either of these programs is glitchy or has bugs?
Suppose that there are bugs that cause erroneous answers. Will they send you a correction without charge, or do you have to pay an annual fee for this (or even buy a later edition of the software because the software that you have is no longer supported?

How do you find the support that is provided to questions?

RE: Post-Tensioning Software

ajk1

(Structural)

(OP)

25 May 17 17:33

To SethGuthrie - would be interested if it does not take too much time, as right now I am trying to get something else completed.

RE: Post-Tensioning Software

Celt83

(Structural)

25 May 17 19:37

Ram Concept is great but has several limitations and work arounds that apply to certain situations, this can be said for all software.
Seth and Karl over at Bentley are excellent when it comes to technical support for the product. Bentley as a whole and their licensing departments though are an entirely different story. If you are the only person using the software then their license model may be OK for you but if anyone else is going to use it prepare to get raked over the coals by quarterly fees that you will have no practical means to prevent.

I've personally never used Rapt but have heard great things about it and the Rapt user here on the forums always seems to post some excellent information.

RE: Post-Tensioning Software

KootK

(Structural)

25 May 17 19:46

Any chance that would be Karl Gullerud?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Post-Tensioning Software

Celt83

(Structural)

25 May 17 19:50

KootK: yep

Those two are a good chunk of the reason we haven't turned our backs on the RAM products completely during this licensing extortion practice Bentley has been running.

RE: Post-Tensioning Software

SethGuthrie

(Civil/Environmental)

25 May 17 19:57

We are in the testing phase of the revised Connected Licensing which reintroduces license usage restrictions. Thanks for your patience while we test this and try to get the performance speed improved. Rather than high jacking this thread which is about post-tensioning, anyone who wants to know more about this can contact me via email or Bentley Communities. (and yes, that's was Karl Gullerud, one of our very best).

RE: Post-Tensioning Software

rapt

(Structural)

25 May 17 23:39

ajk1

Any input in RAPT that is related to a location from a support can be defined from any support. In general, RAPT will then convert the dimension to the nearest support to the left of the location. Except for reinforcement as below

For reinforcing bars, "support type" bars are defined from the support they relate to (dimensions to left and right from that support). "Span type" bars are dimensioned from the supports at each end of the span.

US and real Canadian bar sizes are pre defined. Plus the user can create/modify their own set of default data and define anything they want.

RE Utilization Ratio, never needed one. RAPT shows a graphic plot showing
- the moment capacity required
- the capacity of defined tendons and reinforcement
- the final capacity provided including program calculated reinforcement.
- the minimum Capacity required

RE: Post-Tensioning Software

ajk1

(Structural)

(OP)

26 May 17 23:02

To rapt:

Sounds interesting, particularly the way the rebar is defined.
From whom and where is it marketed, and where can we find more information about it, including costs, etc.?
Is there a trial version available?

RE: Post-Tensioning Software

hokie66

(Structural)

26 May 17 23:34
http://www.raptsoftware.com/

ajk1,

RE: Post-Tensioning Software

Ingenuity

(Structural)

27 May 17 02:06

Quote (ajk1)

We generally have not run into significant cracking issues, or any deflection issues, although that could certainly happen.

A significant number of PT structures that I have been involved that were constructed in the late 60's/early 70's have had excessive cracking and deflection problems, with the majority of those being 2-way banded/uniform slabs that had too thinner slabs.

One notable project from 2003, was a roof level 2-way slab parking structure from the early 70's that 'lost' 50% of its banded tendons parallel with a slab edge (due to corrosion) with resulting midspan defections of 4"+ for a 5-½" thick slab with 25.5' spans:



Slab was emergency shored, then we did some temporary external PT (designed with RAPT software) consisting of 4 tendons with galvanized steel deviators, harped:



It was a temporary fix to 'buy' some time (12 months) for the owner to raise the funds to eventually demolish the roof deck and replace.

A significant number of PT structures that I have been involved that were constructed in the late 60's/early 70's have had excessive cracking and deflection problems, with the majority of those being 2-way banded/uniform slabs that had too thinner slabs.One notable project from 2003, was a roof level 2-way slab parking structure from the early 70's that 'lost' 50% of its banded tendons parallel with a slab edge (due to corrosion) with resulting midspan defections of 4"+ for a 5-½" thick slab with 25.5' spans:Slab was emergency shored, then we did some temporary external PT (designed with RAPT software) consisting of 4 tendons with galvanized steel deviators, harped:It was a temporary fix to 'buy' some time (12 months) for the owner to raise the funds to eventually demolish the roof deck and replace.

RE: Post-Tensioning Software

ajk1

(Structural)

(OP)

28 May 17 02:55

To Hokie66
Thanks for the link. I see that Rapt does not have the Canadian (CSA A23.3) Standard, which differs from the American (ACI-318) Standard, and although it does list the ACI Standard, it is the 1999 ACI which is by now well out of date, although I do not know if the current ACI has significant differences. On the other hand, it seems to do columns with sloping capitals (which ADAPT incredibly does not do) and seems to have a much neater and more conventional way of specifying the rebar end locations. If I have time I will try to use their demo.

To Ingenuity:

The garage we are most involved with currently is one way non-prestressed slab supported on post-tensioned beams, although in the past we have also investigated 2-way flat slab system. Was the 25.5 feet clear span or centre-to-centre span? 5.5" thick p.t. slab (span/thickness = 55±) seems way too much, if the span is the clear span. The photos that you included are very interesting and look like a neat solution, even though temporary.

I note that the tendons are not encased. I suppose that is ok for a 12 month maximum period, and the owner does not significantly extend the 12 months (as I find can happen when we tell an owner that a fix has a given temporary life). If one of those unencapsulated tendons should eventually fail due to corrosion or any other reason, it would be a significant public safety hazard, but I expect that you considered that. I suppose the lack of fire protection could also be justified on the basis that it is a temporary emergency fix.

The deviators look neat and well thought out. Would you have a photo of the anchorage for the ends of the tendons?

RE: Post-Tensioning Software

hokie66

(Structural)

28 May 17 04:54

ajk1,
I think that part of the page I linked is out of date. For better information about the current standards, I suggest you contact Gil Brock directly by phone or the email address listed on that page. He doesn't bite.

RE: Post-Tensioning Software

rapt

(Structural)

28 May 17 06:30

ajk1,

RAPT includes Canadian (CSA A23.3) Standard and Canadian materials. You should contact me privately with any more questions. Eng-Tips will start to regard this as a commercial discussion if we continue!!!

Agree with you about the L/D. Too many designs are being done with very thin slabs. I was only discussing this privately yesterday with Ingenuity on another project where the L/D ratio is about 48.

There are 2 problems with this. Ductility and vibrations along with the incorrectly calculated deflections. Any PT slab with an L/D > 40 needs to be checked carefully for vibrations. And those checks need to allow correctly for cracking! Anyone doing an average moment banded/distributed design to ACI318 and allowing the stresses to reach the ACI limit for "Class Uncracked", is actually going to end up with a cracked structure, because the real stresses are significantly higher than those being used for the check, plus restraint stresses have not been included!

RE: Post-Tensioning Software

ajk1

(Structural)

(OP)

28 May 17 16:15

ok, thank you both.

RE: Post-Tensioning Software

Ingenuity

(Structural)

28 May 17 22:40

Quote (ajk1)

Was the 25.5 feet clear span or centre-to-centre span? 5.5" thick p.t. slab (span/thickness = 55±) seems way too much, if the span is the clear span.

25.5' was centerline span. 12" dia. circular columns with 4' square inverted truncated pyramid capitals. Vibration was so excessive immediately after construction that W16 steel beams were attached (hung) from the underside of slab along both column line directions to reduce effects.

Quote (ajk1)

If one of those unencapsulated tendons should eventually fail due to corrosion or any other reason, it would be a significant public safety hazard, but I expect that you considered that.

Yes, but the nice thing with external tendons is that they are available for continuous and easy inspection along their whole length...but, vulnerable to vandalism...albeit that the vandals would only get to 'play' with such once in their lifetime!

Quote (ajk1)

I suppose the lack of fire protection could also be justified on the basis that it is a temporary emergency fix.

These particular strand tendons were somewhat of a new technology at the time (2002/3), greased and sheathed with a special intumescant coating that would provide a 30 minute FR, and given the open-air parking structure the AHJ was okay with the approach.

Quote (ajk1)

Would you have a photo of the anchorage for the ends of the tendons?

The four (4) tendons were double live-end stressed (300+ feet long structure), terminated with 2" thick x 10" square custom galv bearing plate with barrel chucks and wedges:



Upon completion of the stressing, the tails were cut from one-end and a galvanized top-hat cap, grease filled, with rubber gasket, was stainless steel screw attached to the bearing plate. Similar to this thread back in April 2017



One of the live-ends was left with 4' long tails and the top-hat was modified to incorporate an extended galv tube with end cap to accommodate and protect the tails, so that when it came time to demolish the roof structure the external PT tendons could be de-stressed safely with ease, simply unbolt the extended end cap, and hydraulically de-stress the tendons, in multiple strokes. Somewhat like this sketch:

25.5' was centerline span. 12" dia. circular columns with 4' square inverted truncated pyramid capitals. Vibration was so excessive immediately after construction that W16 steel beams were attached (hung) from the underside of slab along both column line directions to reduce effects.Yes, but the nice thing with external tendons is that they are available for continuous and easy inspection along their whole length...but, vulnerable to vandalism...albeit that the vandals would only get to 'play' with such once in their lifetime!These particular strand tendons were somewhat of a new technology at the time (2002/3), greased and sheathed with a special intumescant coating that would provide a 30 minute FR, and given the open-air parking structure the AHJ was okay with the approach.The four (4) tendons were double live-end stressed (300+ feet long structure), terminated with 2" thick x 10" square custom galv bearing plate with barrel chucks and wedges:Upon completion of the stressing, the tails were cut from one-end and a galvanized top-hat cap, grease filled, with rubber gasket, was stainless steel screw attached to the bearing plate. Similar to this thread back in April 2017 Link . Bearing plate was PU caulked around perimeter.One of the live-ends was left with 4' long tails and the top-hat was modified to incorporate an extended galv tube with end cap to accommodate and protect the tails, so that when it came time to demolish the roof structure the external PT tendons could be de-stressed safely with ease, simply unbolt the extended end cap, and hydraulically de-stress the tendons, in multiple strokes. Somewhat like this sketch:

RE: Post-Tensioning Software

hokie66

(Structural)

29 May 17 02:44

Those skimpy designs from the past certainly keep you busy, Ingenuity. But then, I expect that some of today's designs and construction practices will continue the tradition.

RE: Post-Tensioning Software

ajk1

(Structural)

(OP)

29 May 17 16:34

To Igenuity:

Very interesting.

Against what was the end plate placed? Was there a wall each end?

Did the intumescent coating have any moisture barrier properties to prevent condensation on the strand and corrosion?

Have you ever used an intumescent coating on strands where an inspection opening was chipped into the slab soffit and a removable cover plate installed (to allow future inspection on the strands)?

RE: Post-Tensioning Software

Ingenuity

(Structural)

29 May 17 23:15

Quote (hokie66)

Those skimpy designs from the past certainly keep you busy, Ingenuity. But then, I expect that some of today's designs and construction practices will continue the tradition.

You speak the truth. Skimpy design coupled with on-site 'fixes' to tear/nicks/cuts to heat-sealed sheaths of the past that were done with tie-wired kraft paper, with no waterproofing to the roof deck, it is just a matter of time that they break down:



The encapsulated PT system of today are far superior to that from the 60's through 80's, but some current site practices, with 'black-box' designs leave me questioning.

Quote (ajk1)

Against what was the end plate placed? Was there a wall each end?

No end/corner walls, just an existing corner column condition made up of 12" circular column and existing cut-off truncated pyramid capital - we cored horizontal drill 2" diameter holes thru caps, with obvert of hole flush with underside of slab. End details like this scaled sketch:



The depth of the existing capital was substantial, but we did introduce an end eccentricity to accommodate the anchorage location.

There were a few parallel and perpendicular exterior walls and we made up custom steel deviators to take care of the harped tendon forces:



The perpendicular wall details was simply a CMU through-hole with steel deviator pipe to reduce masonry bearing stresses.

Quote (ajk1)

Did the intumescent coating have any moisture barrier properties to prevent condensation on the strand and corrosion?

The intumescent coating is integral with the strand/sheath system, and has the appearance and touch of a typical PT sheath (HDPE or Polypropylene), albeit a little thinner, and not as pliable. During the manufacture of the unbonded tendon (after the 7-wire strand manufacturing process), the bare strand goes through a grease bath, then immediately following, molten HDPE pellets are applied to create a thin HDPE sheath, that is water cooled, then a proprietary intumescent, woven-cloth reinforced FR material is applied immediately following, that bonds to the sheath, so their is no air space between the sheath and the FR, then an outer protective sheath is bonded to that. I think that is how is it manufactured - been more than 10 years since we last used the product.

On another project, FR was addressed by metal lathe and vermiculite plaster - awful product to hand apply, and the finished product looks awful too.

Have also used larger diameter continuous HDPE pipe/duct with tendons placed inside, then cement grouted the pipe. Looks way better than a plastered FR tendon, but in reality you don't actually get the FR along the full length especially at the deviation points where the tendon bears tight to the pipe/duct so no 'cementitious' cover here.

You speak the truth. Skimpy design coupled with on-site 'fixes' to tear/nicks/cuts to heat-sealed sheaths of the past that were done with tie-wired kraft paper, with no waterproofing to the roof deck, it is just a matter of time that they break down:The encapsulated PT system of today are far superior to that from the 60's through 80's, but some current site practices, with 'black-box' designs leave me questioning.No end/corner walls, just an existing corner column condition made up of 12" circular column and existing cut-off truncated pyramid capital - we cored horizontal drill 2" diameter holes thru caps, with obvert of hole flush with underside of slab. End details like this scaled sketch:The depth of the existing capital was substantial, but we did introduce an end eccentricity to accommodate the anchorage location.There were a few parallel and perpendicular exterior walls and we made up custom steel deviators to take care of the harped tendon forces:The perpendicular wall details was simply a CMU through-hole with steel deviator pipe to reduce masonry bearing stresses.The intumescent coating is integral with the strand/sheath system, and has the appearance and touch of a typical PT sheath (HDPE or Polypropylene), albeit a little thinner, and not as pliable. During the manufacture of the unbonded tendon (after the 7-wire strand manufacturing process), the bare strand goes through a grease bath, then immediately following, molten HDPE pellets are applied to create a thin HDPE sheath, that is water cooled, then a proprietary intumescent, woven-cloth reinforced FR material is applied immediately following, that bonds to the sheath, so their is no air space between the sheath and the FR, then an outer protective sheath is bonded to that. I think that is how is it manufactured - been more than 10 years since we last used the product.On another project, FR was addressed by metal lathe and vermiculite plaster - awful product to hand apply, and the finished product looks awful too.Have also used larger diameter continuous HDPE pipe/duct with tendons placed inside, then cement grouted the pipe. Looks way better than a plastered FR tendon, but in reality you don't actually get the FR along the full length especially at the deviation points where the tendon bears tight to the pipe/duct so no 'cementitious' cover here.

RE: Post-Tensioning Software

ajk1

(Structural)

(OP)

30 May 17 21:32

To Ingenuity - your detailed description and elegant sketch makes things very clear. Looks like a very well thought out and detailed job. Your "Ingenuity" name is well deserved. You should have won an award for this job, but I guess success is its own reward. Thanks very much.

RE: Post-Tensioning Software

Ingenuity

(Structural)

31 May 17 05:47

Quote (ajk1)

You should have won an award for this job, but I guess success is its own reward.

Thank you, very nice of you.

This parking structure was part of a condominium association (you know, run like a political subcommittee, with 250 owners all with their agendas), so my older, cynical self is 'rewarded' when: 1) get paid 100% in a reasonable time frame, AND 2) don't get dragged into a legal suit.

All the best for your PT software research.

Thank you, very nice of you.This parking structure was part of a condominium association (you know, run like a political subcommittee, with 250 owners all with their agendas), so my older, cynical self is 'rewarded' when: 1) get paid 100% in a reasonable time frame, AND 2) don't get dragged into a legal suit.All the best for your PT software research.

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