INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Ruiyi supply professional and honest service.

Contact US

FIRST NAME

*

LAST NAME

*

EMAIL

*

MESSAGE

*

ADDITIONAL DETAILS

Thanks. We have received your request and will respond promptly.

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!

• Talk With Other Members
• Be Notified Of Responses
  To Your Posts
• Keyword Search
• One-Click Access To Your
  Favorite Forums
• Automated Signatures
  On Your Posts
• Best Of All, It's Free!

Join Us!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Students Click Here

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Eng-Tips Posting Policies

Contact US

Interview help - post tension design using hand calculations

5

thread507-415964 Forum Search FAQs Links MVPs

• Forum

• Search

• FAQs

• Links

• MVPs

Interview help - post tension design using hand calculations

Interview help - post tension design using hand calculations

sparta7963

(Structural)

(OP)

19 Oct 16 23:27

Hi, I am a attending an interview with a company which does Post tension work. The job position is 'Structural Engineer - Post Tension Design'. I was told by the recruitment agency that the company will do a technical round interview where i have to use hand calculation in post tension design. I have about 5 years experience as a structural engineer but never done post tension design. Can you please tell me the some question that I might be asked in 'Post tension design' and what sort of hand calculations i have to do. I am in UK, so please provide me some study materials based of BS/EURO code. Thank you.

RE: Interview help - post tension design using hand calculations

Retrograde

(Structural)

20 Oct 16 00:07

In the UK you will need to be familiar with the Concrete Society Technical Report No. 43: Post-tensioned concrete floors.

RE: Interview help - post tension design using hand calculations

sparta7963

(Structural)

(OP)

20 Oct 16 00:29

Thanks mate.. any particular questions you can think of?

RE: Interview help - post tension design using hand calculations

TehMightyEngineer

(Structural)

20 Oct 16 00:34

I'd learn about jacking procedures, transfer design stages, and prestressing losses; to name a few problems they may ask. Some other aspects might be various steps in checking capacity or whether the member remains uncracked. I'm familiar with the US codes so I can't help with any specifics beyond just generalizations.

Not meaning to judge but it seems like you're applying for a job you're not currently qualified for. While you can certainly learn on the job and study outside of work, do you feel you're able to take on the responsibilities they'll be needing from you?I'd learn about jacking procedures, transfer design stages, and prestressing losses; to name a few problems they may ask. Some other aspects might be various steps in checking capacity or whether the member remains uncracked. I'm familiar with the US codes so I can't help with any specifics beyond just generalizations.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
www.americanconcrete.com

RE: Interview help - post tension design using hand calculations

Ingenuity

(Structural)

20 Oct 16 00:53

At an job interview (many decades ago when I had about 3 or 4 years of grad experience) with a PT company in their design branch/office, I recall being asked by their chief engineer to discuss the steps to design a PT flat slab (nothing too difficult: selection of slab thickness, check punching shear, select load to balance, flexure, deflection etc), and then hand calculate the 'balanced load' for a given tendon drape and prestress force for an internal span of a beam. I had done 2 or so courses of undergrad prestressed concrete subjects at uni so they questions were not really a big deal.

I got the job, but I will say that it was "balls to the wall" upon starting on the first day. Thrown some interesting, multiple, fast-paced projects in the first week!

Not wanting to turn you off - but if you do go past the interview phase and land the job, I am going to assume it will be fast-paced from the get-go. If you don't have the fundamental basic understanding of PT, they may not be willing to slow down and train/mentor you.

Design software has (unfortunately?) changed a few things over the years, on what you can 'get away with' on assumed-knowledge.

Did you take a class at uni on prestressed concrete?

Are you in AU or the UK?

RE: Interview help - post tension design using hand calculations

sparta7963

(Structural)

(OP)

20 Oct 16 01:06

Thanks Ingenuity, i was working in the UK, i just moved to Aus and post tension jobs seem to be very hot here.
I understand the risks of a new job, but i can either sit at home dreaming about an ideal job Or work hard and make use of a given opportunity. Hopefully i should be able to manage will try to study what you have mentioned..
any particular study material u propose other than TR43 (Concrete Society Technical Report No. 43: Post-tensioned concrete floors)?

RE: Interview help - post tension design using hand calculations

Ingenuity

(Structural)

20 Oct 16 01:21 sparta7963,

Since you are currently in AU I would grab a copy of one or both of the following AU underdrad text books on prestressed concrete:

1. Prestressed Concrete, 3rd Edition. Robert Warner, Ken Faulkes, Stephen Forster,

2. Design of Prestressed Concrete to AS3600-2009, Second Edition, Raymond Ian Gilbert, Neil Colin Mickleborough, Gianluca Ranzi

Available from most uni bookshops.

Even if you get an older 2nd-hand copy of Warner/Faulkes book (late 80's or early 90's edition I think), that has some good practical design info that will be an advantage to you at minimal cost.

The second text does a better treatment of the theoretical aspects of prestressed concrete (especially creep, shrinkage, deflection etc), but the first text has some good info for practical design of slabs and beams: step-by-step procedures and design examples.

And forget about UNbonded PT - AU is all bonded/grouted PT.

All the very best to you.

Also - if you want a heads-up on PT software in AU - most (all?) consulting companies in AU (and beyond) use RAPT (

Since you are currently in AU I would grab a copy of one or both of the following AU underdrad text books on prestressed concrete:Available from most uni bookshops.Even if you get an older 2nd-hand copy of Warner/Faulkes book (late 80's or early 90's edition I think), that has some good practical design info that will be an advantage to you at minimal cost.The second text does a better treatment of the theoretical aspects of prestressed concrete (especially creep, shrinkage, deflection etc), but the first text has some good info for practical design of slabs and beams: step-by-step procedures and design examples.And forget about UNbonded PT - AU is all bonded/grouted PT.All the very best to you.Also - if you want a heads-up on PT software in AU - most (all?) consulting companies in AU (and beyond) use RAPT ( www.raptsoftware.com ) and if you go to their website I think there is a trial download where you can take it for a spin. The author and owner of RAPT visits here at Eng-Tips frequently, so hopefully he will chip in too.

RE: Interview help - post tension design using hand calculations

Retrograde

(Structural)

20 Oct 16 03:24

In your first post you said you were in the UK but now you are saying you are in Australia? If you are in Australia then TR43 is not in wide use although it is still worthwhile to read through.

The RAPT manual is a good resource (all 740 pages of it!). There is good discussion on preliminary sizing, load balancing and level of prestress in the beginning of the "Theory" section.

RE: Interview help - post tension design using hand calculations

rapt

(Structural)

20 Oct 16 03:52

Sorry, I am with TehMightyEngineer on this one. if you have absolutely no idea on how to do PT design, bluffing them into thinking you do is not the way to go in my opinion. If they know what they are doing, they will pick it very quickly and then you have no chance.

If you really understand concrete design, convince them of that. The step up to PT design is not that large if you understand engineering, structures and concrete design (and I mean understand, not just know how to design an RC slab using software). By all means read the books to get started, but I would be honest. They will not expect many people coming from Europe to have much building PT experience.

RE: Interview help - post tension design using hand calculations

sparta7963

(Structural)

(OP)

20 Oct 16 09:17

thanks for the honest reply guys. I have around 5 years of experience in reinforced concrete and steel structures and i have mostly done multi-storey residential buildings, some industrial buildings and warehouse structures. I am not very experienced with PT design but however the job requirement is not very high i guess, more like they are expecting a candidate with 1-3 years of experience.

From what I have seen in my job hunting, australian companies don't consider or value your experience outside australia (that what the ALL the job recruitment consultants told me and the salary offered for that position was between AUD$60000 - $70000). So i am guessing its more of a junior level position.

RE: Interview help - post tension design using hand calculations

KootK

(Structural)

20 Oct 16 12:41

Employer: vet you to ensure that they're getting what they need.

Candidate: chase down your dreams with as much courage and tenacity as you can muster.

If I could somehow convince NASA to hire me to train for the next manned space flight, would I give it a go? Darn right.

Must the next prime minister have previous experience being prime minister? Of course not. Many jobs are learned on the job. Meaningful personal growth usually requires reaching a little.

I feel that the obligations of the employer and candidate here are as follows:Employer: vet you to ensure that they're getting what they need.Candidate: chase down your dreams with as much courage and tenacity as you can muster.If I could somehow convince NASA to hire me to train for the next manned space flight, would I give it a go? Darn right.Must the next prime minister have previous experience being prime minister? Of course not. Many jobs are learned on the job. Meaningful personal growth usually requires reaching a little.

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: Interview help - post tension design using hand calculations

KootK

(Structural)

20 Oct 16 12:50

TR43 would seem to be the best place to start. If you google VSL + post-tensioned concrete, you'll find a number of free - and relatively short - design brief documents. If you've got a bit a time to prepare, I'd recommend TY Lin's text. It's reasonably short and great for the fundamentals. It also has a number of simple examples.

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: Interview help - post tension design using hand calculations

boo1

(Mechanical)

20 Oct 16 15:40 http://www.ptia.org.au/Downloads.aspx

RE: Interview help - post tension design using hand calculations

BUGGAR

(Structural)

20 Oct 16 18:27

Isn't it all just P/A plus or minus Mc/I, and knowing at what times certain stresses apply? (Consider this an interview level response).

RE: Interview help - post tension design using hand calculations

rb1957

(Aerospace)

20 Oct 16 18:32
"I haven't done any PT projects, but I have reviewed some technical references ..."

I'd be interested in when to use PT beams, and why (are they used in those situations).

my 2c, don't over-sell yourself, but it's really good to show you've done some prep work ..."I haven't done any PT projects, but I have reviewed some technical references ..."I'd be interested in when to use PT beams, and why (are they used in those situations).

another day in paradise, or is paradise one day closer ?

RE: Interview help - post tension design using hand calculations

WARose

(Structural)

20 Oct 16 21:17

I haven't read through the other replies (other than noting you've gotten some good technical advice) so pardon me if this has been said before but: whatever you do, be darn sure they understand what you can and can't do. It's one thing for them to quiz you or whatever.....but make clear: "Hey, however I did on the quiz, this is my first time at bat with post-tension design."

You just want them aware of your experience level......especially if they want you to come in and immediately stamp stuff (you may not be comfortable with that).

One of the best jobs I ever had was when I told the guy in the interview: "Your ad asked for [this or that skill]....here are some of those skills I have: [ ], and here are some I don't have: [ ]."

RE: Interview help - post tension design using hand calculations

Ingenuity

(Structural)

20 Oct 16 21:28

Quote (WARose)

and immediately stamp stuff

That won't be an issue - there is no PE/SE stamping in AU, per se.

Stamping/sealing is a somewhat unique North American "restrictive trade practice".

That won't be an issue - there is no PE/SE stamping in AU, per se.Stamping/sealing is a somewhat unique North American "restrictive trade practice".

RE: Interview help - post tension design using hand calculations

Ingenuity

(Structural)

20 Oct 16 21:36

Quote (rb1957)

I'd be interested in when to use PT beams, and why (are they used in those situations).

Is that you asking, rb?

If so: Typically, PT (and prestressing generally) is used to 1) accommodate larger spans at 2) less structural depth than non-prestressed members, with 3) superior deflection control due to the active 'actions' of eccentricity/curvature of the prestressing tendons, and 4) less cracking due to the effective P/A. Also good for fatigue resistance too - more appropriate for bridges than buildings.

Is that you asking, rb?If so: Typically, PT (and prestressing generally) is used to 1) accommodate larger spans at 2) less structural depth than non-prestressed members, with 3) superior deflection control due to the active 'actions' of eccentricity/curvature of the prestressing tendons, and 4) less cracking due to the effective P/A. Also good for fatigue resistance too - more appropriate for bridges than buildings.

RE: Interview help - post tension design using hand calculations

Trenno

(Structural)

20 Oct 16 21:37

Coming more from the practical perspective, I highly recommend downloading the material available from the Post Tensioning Institute of Australia.

http://www.ptia.org.au/Downloads.aspx

In particular the 'Practical Prestress Detailing' guide. I've attached it for anyone too lazy to click the link.

• http://files.engineering.com/getfile.aspx?folder=e48d3b28-f7d0-49a3-96b9-a3

+1 for the RAPT manual. Great reference, but it doesn't cover it all. Do some research on load balancing and Hall's graphical method.Coming more from the practical perspective, I highly recommend downloading the material available from the Post Tensioning Institute of Australia.In particular the 'Practical Prestress Detailing' guide. I've attached it for anyone too lazy to click the link.

RE: Interview help - post tension design using hand calculations

Ingenuity

(Structural)

20 Oct 16 21:46

And don't EVER do this!

RE: Interview help - post tension design using hand calculations

Trenno

(Structural)

20 Oct 16 21:53

Been a while since I've seen that classic ^^

RE: Interview help - post tension design using hand calculations

TehMightyEngineer

(Structural)

For more information, please visit post tension system solutions.

Featured content:
What speed do you need to machining aluminum? 20 Oct 16 22:12

That image would actually make a great interview question; "what's wrong with this picture?".

PEEK vs PEK vs PTFE
ER Collet Basics - Things You Need to Know to Get Started

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
www.americanconcrete.com

RE: Interview help - post tension design using hand calculations

slickdeals

(Structural)

21 Oct 16 22:39

At least the stressing end is shown on the right side

RE: Interview help - post tension design using hand calculations

dik

(Structural)

22 Oct 16 03:49

almost always terminated the strand at the kern point to account for some -ve moment and to increase the sag a tad.

RE: Interview help - post tension design using hand calculations

rapt

(Structural)

22 Oct 16 21:45

Dik

OK for an increase the negative moment capacity, but you also increase your negative moment due to secondary prestress effects, and you are also applying an end moment which completely negates the extra uplift and does nothing to help with deflections or service stresses at mid-span.

Further on the negative side, if the member is not deep enough you are creating congestion problems at the top with anchorages needing to fit in with transverse tendons and reinforcement in both directions.

So unless you really need the extra negative moment capacity (which you normally do not, as I would always add some passive top reinforcement at end columns anyway), don't waste your time.

[Post Deleted]

RE: Interview help - post tension design using hand calculations

dik

(Structural)

1 Nov 16 11:55

agreed to some extent... and add regular reinforcing as noted... running the sums it does improve things a bit... just take advantage of the added sag in the end span.

thanks, Dik

RE: Interview help - post tension design using hand calculations

rapt

(Structural)

2 Nov 16 01:55

What is the added sag doing for you, after you take into account the added end moment which completely negates the extra uplift from the added sag?

RE: Interview help - post tension design using hand calculations

cal91

(Structural)

2 Nov 16 15:26

I don't have any experience in PT, could someone clarify what is wrong with the picture? Thanks!

RE: Interview help - post tension design using hand calculations

KootK

(Structural)

2 Nov 16 16:57

Prestressing tendons experience tension losses due to anchor seating, relaxation, elastic shortening, creep etc. With very short tendons, those losses decrease the prestress to the point that the prestressing ceases to add meaningful benefit to the system. It can also be a bit tricky to jack short tendons accurately as small increments of end stretch produce relatively large increments of tendon force (d = PL/AE).

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: Interview help - post tension design using hand calculations

Ingenuity

(Structural)

2 Nov 16 22:54

Quote (dik)

almost always terminated the strand at the kern point to account for some -ve moment and to increase the sag a tad.

Quote (rapt)

What is the added sag doing for you, after you take into account the added end moment which completely negates the extra uplift from the added sag?

dik,

What rapt refers can be easily understood for a simplistic case of a simply supported beam with end eccentricities ABOVE the CGS. Such end eccentricities makes the midspan deflection worse (less uplift), as per the attached two cases, where I just rearranged 5wL4/384EI and P(e1+e2)L2/8EI for midspan displacements, under the actions due to prestress due to wbal and end-eccentricity of prestress, respectively.

The PL2e2/48EI term is making the midspan uplift LESS compared to CASE II with the same prestress, less "sag", yet with no end eccentricity.

Whatrefers can be easily understood for a simplistic case of a simply supported beam with end eccentricities ABOVE the CGS. Such end eccentricities makes the midspan deflection worse (less uplift), as per the attached two cases, where I just rearranged 5wL/384EI and P(e+e)L/8EI for midspan displacements, under the actions due to prestress due to wand end-eccentricity of prestress, respectively.The PL/48EI term is making the midspan uplift LESS compared to CASE II with the same prestress, less "sag", yet with no end eccentricity.

RE: Interview help - post tension design using hand calculations

dik

(Structural)

3 Nov 16 02:38

Thanks... fully understood...

Dik

RE: Interview help - post tension design using hand calculations

rapt

(Structural)

4 Nov 16 00:19

Ingenuity,

Nice pictures. Wish I could do that!

In Case 1, the drape is e1 + e2, not e1, so the balanced load deflection is 5PL^2(e1 + e2)/48EI.

After subtracting off the end moment effect, Case 1 result is 5PL^2(e1)/48EI, exactly the same as Casse 11.

RE: Interview help - post tension design using hand calculations

KootK

(Structural)

4 Nov 16 00:33

Excuse the quality. I wan't originally intended for public consumption.

I was curious too so I did a little fact checking myself last night ('tis the season). Turns out Inginuity is fit to lead the free world after all. Or at lest design a little PT.Excuse the quality. I wan't originally intended for public consumption.

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: Interview help - post tension design using hand calculations

Ingenuity

(Structural)

4 Nov 16 00:48 rapt - just some mathematical 'gymnastics' to get the reduced form. See below.

Quote (KootK)

Inginuity

KootK - your 'thumb-nail-dipped-in-tar' presentation is as good as your spelling, but that's ok, injinrs are not here on this earth to look good or be great spellers - well at least I'm not!

- just some mathematical 'gymnastics' to get the reduced form. See below.- your 'thumb-nail-dipped-in-tar' presentation is as good as your spelling, but that's ok,are not here on this earth to look good or be great spellers - well at least I'm not!

RE: Interview help - post tension design using hand calculations

Ingenuity

(Structural)

4 Nov 16 00:52

Quote (rapt)

Nice pictures. Wish I could do that!

I did a FEM analysis too - want to see that? Just kidding

I did a FEM analysis too - want to see that? Just kidding

RE: Interview help - post tension design using hand calculations

KootK

(Structural)

4 Nov 16 00:55

I'm actually a first rate speller. I'm just usually doing this on my phone and correcting the autocorrects isn't worth the effort. Even so, I've gotta be in the upper 50% round here with respect to readability.

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: Interview help - post tension design using hand calculations

KootK

(Structural)

4 Nov 16 00:59

Quote (Ingenuity)

I did a FEM analysis too - want to see that? Just kidding winky smile

If you've already got it prepped then... yeah. I think that midspan moments do come out a tie.

If you've already got it prepped then... yeah. I think that midspan moments do come out a tie.

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: Interview help - post tension design using hand calculations

rapt

(Structural)

4 Nov 16 01:02

Sorry Ingenuity, I had always assumed it exactly cancelled the increased uplift effect and commented before looking into the derivation. But looking into the math you are correct, it actually makes your deflection slightly worse, contrary to some designers expectations.

Which would explain why lowering the tendon at the anchorage below the centroid in a simply supported span (and the reverse in a cantilever), reducing the "drape uplift" but introducing a beneficial set of end moments, actually helps reduce deflections.

This is one of the reasons I have always tried to talk designers out of thinking in terms of load balancing. They tend to think of the drape effect only and not the "secondary profiling effects" (as distinct from Secondary Prestress (parasitic moment)) like moments from end eccentricities. "Moment Balancing" is a much safer concept!

Some early PT programs used to actually make those incorrect assumptions regarding raising end eccentricities, even one developed by a PT company you used to work for in Sydney which was taken to America by an employee and has developed and been used extensively in the USA.

RE: Interview help - post tension design using hand calculations

rapt

(Structural)

4 Nov 16 01:07

KootK,

Yes, with a determinate member, the mid span moment is P * e1 no matter what!

RE: Interview help - post tension design using hand calculations

Ingenuity

(Structural)

4 Nov 16 07:41

Quote (rapt)

Sorry Ingenuity

No worries.

Quote (rapt)

Which would explain why lowering the tendon at the anchorage below the centroid in a simply supported span (and the reverse in a cantilever), reducing the "drape uplift" but introducing a beneficial set of end moments, actually helps reduce deflections.

Yep, even if you consider a prestressed plank (and ignore strand end-slip etc) with straight strand of constant eccentricity, e1, [CASE III below] there is 20% more midspan uplift than a parabolic drape of e1 'sag' with the same prestress [CASE II]:

Quote (KootK)

If you've already got it prepped then... yeah.

No, I didn't do a FE analysis. But I concur with rapt with a midspan moment of P*e1.

No worries.Yep, even if you consider a prestressed plank (and ignore strand end-slip etc) with straight strand of constant eccentricity, e, [CASE III below] there is 20% more midspan uplift than a parabolic drape of e'sag' with the same prestress [CASE II]:No, I didn't do a FE analysis. But I concur withwith a midspan moment of P*e

RE: Interview help - post tension design using hand calculations

KootK

(Structural)

4 Nov 16 11:45

What is affected by the tendon disposition elsewhere is the total area under the moment diagram and, by extension, the total area under the curvature diagram and, ultimately, deflection. Since a level tendon profile msximizes the area under the moment diagram, it makes sense that arrangement would maximize deflection.

So, if one were to design a cantilever with the singular goal of inducing upwards tip deflection, the best strategy would be to:

1) Raise the end anchorage as much as possible.

2) Use a concave down parabola to get from the end anchorage elevation to the support tendon elevation.

Both of these things because they "fatten" the moment diagram. But, then, we typically do neither of these things in conventional design for a number of practical reasons.

I find it interesting to consider this in terms of "balancing moment" as rapt suggested. With the extreme tendon position a given, the peak of that moment diagram is unaffected by the tendon disposition elsewhere.What is affected by the tendon disposition elsewhere is the total area under the moment diagram and, by extension, the total area under the curvature diagram and, ultimately, deflection. Since a level tendon profile msximizes the area under the moment diagram, it makes sense that arrangement would maximize deflection.So, if one were to design a cantilever with the singular goal of inducing upwards tip deflection, the best strategy would be to:1) Raise the end anchorage as much as possible.2) Use a concave down parabola to get from the end anchorage elevation to the support tendon elevation.Both of these things because they "fatten" the moment diagram. But, then, we typically do neither of these things in conventional design for a number of practical reasons.

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: Interview help - post tension design using hand calculations

cliff234

(Structural)

4 Nov 16 20:56

There is no way that you will be able to teach yourself p.t. design sufficiently make this prospective employer think you know p.t. - and ethically speaking, you should not try to pass yourself off as being proficient at something you have no experience with. A better solution would be to make the case that you are an intelligent engineer who is eager to learn new things and is self-motivated. (Your message speaks to your eagerness to learn p.t. design.) I think the things most employers look for when hiring new engineers are things that cannot be taught - and eagerness to learn, a willingness and ability to communicate, a good work ethic, a genuine passion for structural engineering and an intelligence and curiosity about the way things work. Teaching p.t. someone how to design p.t. is easy - those other things are not.

RE: Interview help - post tension design using hand calculations

rapt

(Structural)

5 Nov 16 01:22

Kootk,

Yes, the best for deflection. But when pushed too far you start causing transfer stress problems!

If he was alive today, poor old TY Lin would not like our conclusions regarding Load Balancing vs Moment Balancing, but Leonhardt and Guyon surely would.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login

News

Concrete
Post-tension Slab Checklist

copyright 2007 Marshall Hansen

• Rev. 20081026 (powder puff link)
• 20080422 This is the most popular page in my blog and I sincerely appreciate all who stop to look. This list is compiled from field notes and observations. I’m adding more comments as I see issues in search inquiries. Also, I will be trying to (re)organize the list sequentially though many issues occur concurrently and many issues apply to any slab pour. The simplest advice I can give to anyone is follow the plans. If you do this the risk belongs to the engineer and architect for the design. Any change from plans must be in writing – RFI or letter from PT engineer
• this applies primarily to light duty PT, multi-family/residential from GC point of view
• please add any suggestions or comments in the comment box and I may add them to the list
• see another construction management checklist: Powder Puff Cleaning Checklist
• link to this page as I will be updating continually – when you need it you will have my latest edition. https://marshansen.wordpress.com/post-tension-slab-checklist/

Scope/contract issues

• Manpower required to maintain schedule, non-performance will be supplemented
• Daily reports to site Superintendent from sub foreman – # in crew, work done, comments
• Daily and on-going clean-up, non-performance will be supplemented
• 24 hour notices to be one time per condition, failure to act 2nd/subsequent time does not require notice to supplement
• No tolerance harassment policy – wolf whistles, gestures, ogling, yelling, etc.
• Sub is experienced in proper methods of PT components installation and storage of tendons
• Sub will install all materials per manufacturers’ specs or assume responsibility (waterstops, etc)
• Method of elongation spelled out – how tendon is marked, who observes, who gets copies of lab report, etc
• Batch mix and slump, flyash max, additives, if any
• Test cylinder break schedule – 3, 14, 28, extra; 7, 14, 28, extra; etc
• Notes on PT engineer’s plans are requirements for install (while they may not be specified in scope)
• English speaking supervisor/foreman on site at all times
• Sub will be included in pro rata LDs if schedule is not maintained
• Immediately after pour sub will clean area around pump truck and spoils from trucks going to clean out area if on finished pavement
• When form and finish crews are different sub-subs main concrete sub will have management on site throughout process start to finish/clean up
• Inspection, permissions of off-site access for placement of pump truck if site layout will not accommodate pump truck for pour
• When asking for bids if one subcontractor’s price is substantially lower than the other bids consider the possibility that the take-off is wrong, they have not read the specs/plans or made an error in calculations – probably all three. Be prepared for a request to re-engineer the slab using less concrete. The lowest bid does not always save you money

Pre-pour

• Are there any discrepancies between Architectural and Post-Tension Engineer plans? Check all dimensions and features. If so, RFIs must be obtained to proceed, meanwhile,
• Check site layout for building orientation – is it mirrored or flipped from Architectural drawings?
• Are pilings required? They should be done by now and that’s another checklist, my friend.
• Inspection checklist showing required inspections from engineer, architect, client, city, county, parish, municipality, ACOE, state or appropriate enforcement division(s), who calls them in? Copies to GC at site
• Were lifts built up per soil engineer’s specs? Was sub-grade properly compacted? Did lab perform Proctor field test?
• Call surveyor to stake envelope and finished floor or other reference elevation/points as needed/desired (elevator pit) verify
• Envelope placement – four corners and reference other site benchmarks – verify
• Safety – rebar caps w/metal insert (no poke through), barricades around open excavations and forms, safety rails where necessary, trenches for access to elevator pit, OSHA conforming access. Continuous check
• Electricity available for form carpenters (temporary power) or do they have generator?
• Is slab elevation per plans – verify with surveyors stake
• MEP – other trades rough complete and inspected
• Verify all sleeves and proper placement for any utilities under slab, check PT engineer’s plans/spec for placement requirements
• Elevator pit layout – verify
• Elevator pit may require sleeves for sump pump pipes, etc. Verify size and placement
• Elevator base may have sump pit – verify location and dimensions. Confirm with plumber’s submittal for sump pump dimensions
• Is waterproof membrane/Bentonite required under elevator pit base? Coordinate with concrete sub
• Does elevator base have water stop flange or membrane? Does sub have on site? Does sub have proper iron to make watertight joint on site? Keyways? Do you have mfg installation requirements? verify
• Trenches proper depth/width
• Beams and footing proper dimension and shape
• Are there special footings/thickened beams for stairs, chimneys, steel columns, structural features – where, shape, how deep and wide, rebar, etc.
• Slab forms proper elevation relative to pad for slab thickness
• Termite treatment and inspection
• Vapor retarder properly installed, coverage and material per spec (6, 8, 10 mil etc)
• Forms checked per Architectural drawings, check details pages
• Forms properly braced to withstand hydrostatic pressure
• Are two-sided forms properly braced and tied off – inside and outside?
• Are steel form systems properly assembled, anchored, braced, w/ strongbacks, etc?
• Is slab insulation required and on site? Installed properly?
• Block-outs, recessed areas for tile floors, marble thresholds, ADA showers properly formed
• Release (plastic, oil, silicone, diesel, etc) on brick ledge forms on flat areas so they can be removed without damaging, chipping , finished slab. Convenient but not required. Spec may have note on release agents accepted
• Brick ledges continuous around columns and returns verify per plans
• Slope floor in rooms with floor drains – formed or marked with stake for hand finishing
• No slope of approach to exceed ADA (per plans or half of entries)
• Control joint and forms properly set, dowels level/on proper plane and stationary – strip form on proper side
• Tub box placement, ballast, depth, properly installed – cavity for p-trap chase on proper side
• Proper size of rebar per plans/spec
• Post-tension cable anchors installed facing the proper direction – dead and live ends
• Post-tension cables and rebar properly spaced, chaired and tied per plans and mfg specs
• Corners, beams, walls and footings properly reinforced with rebar – hairpins per plans, if required
• Proper tie-in of chairs to post tension cables at intersections and chairs under rebar in beams and footings – this is repeated because it is neglected – look again. If they are not tied to tendons they will get knocked off by finishers during pour
• Plumber check for obvious damage to risers, etc. from form crew, termite applicator. Check 10 foot head or air re-test per specs
• Verify batch mix with spec, sub and plant – fly ash, slump, curing compound
• Plan placement of concrete pump at least one day ahead and ensure access through site to pour. Are any powerlines adjacent to pour? Do you have trenches from electric primaries, civil – storm sewer, sanitary sewer, water, etc and were they compacted properly? Flag off any unstable areas, coordinate with concrete sub
• Order light tower(s) to be delivered the afternoon before an early morning pour. Verify
• Verify sub has sufficient crew to properly finish slab in workable time
• Verify finisher crew arrival time – coordinate with pump truck and plant
• What is weather forecast? Hot , cold, wet, low humidity??
• Are power trowels on site?
• Is curing compound on site, staged near slab? Does sub have operable applicator/sprayer?
• Have these phone numbers already entered in your cell phone and PDA
  • 911 or local emergency direct number if using out-of-state cell phone (call county they will give you direct number)
  • Concrete sub PM, lab, pump, plumber, concrete sales rep, back-up GC staff, emergencies and extra labor needed
  • Printed directions to hospital

• plan truck cleanout area if not on site plans. Low cleanout dumpster with liner can be ordered from pump/dumpster/waste company. Plan delivery one day ahead and clearly mark off limits for construction trash until after pours are completed. Do not create mud pit
• EPA entrance or wash area for truck tires ready to minimize mud, silt carried off-site
• Pipe risers, drains, in floor receptacles, clean outs capped, plugged or taped to prevent dirt and concrete contamination, tops and covers set at right height relative to finished floor surface – level with finished surface VCT, carpet, slab, etc verify with plumber and electrician
• Low temperature pours require blankets. Be sure there are enough on site to cover the pour and you have materials (weights) to hold the blankets on the slab.
• Are there any city noise ordinances restricting construction noise to specific times? Will this affect early morning pours?

Pour

• Plumber(s) on duty ready to work – mud boots, pvc saw, cleaner and glue, markers, tub boxes, sand, pvc fittings and pipe, spare clean outs, laser level, etc.
• Anchors for sill plates per spec (bolts, depth, type, spacing )
• Anchors properly spaced in shear walls
• Steel footings or j-bolts for steel column/post placement – with template
• Call lab for pour inspection (lead time varies per lab), slump and test cylinders, what is required in spec?
• Record truck number, time of delivery, slump – if too wet/dry, if water added
• Verify designed batch mix and strength with plant and truck documents, during pour track travel time from plant to site
• All door thresholds recheck for level
• No added water unless specifically allowed in batch design with required number of revolutions of mixer reached, verify
• If primary concrete sub hires sub finisher they must have crew/agreement to clean all spoils, butter around clean out area and pump truck during/after each pour (it may be in the scope but make sure they are there to do it)

Post pour/finishing

• No slope or broom on thresholds
• Broom entries perpendicular to slope not parallel with slope
• Curing compounds, sealers, hardeners, pump sprayer, misters, etc ready for application per specs, manufacturer’s instructions and plans
• Observe power trowel operators – are they hitting pipes?
• When do you pull first pull and when do you pull final pull is based upon plans, engineer plan notes (usually on PT pages) and/or specs. First pull is usually within x days of pour. The lab will break cylinders based upon the schedule you give them and the final pull will occur once a PSI threshold is reached. This number is also in plans/specs. If not call your PM if PM doesn’t know call PT slab engineer.
• Coordinate, verify elongation process/method and recording with sub and lab before first pull. How is length marked, measured, cylinder break x days after pour, etc.
• Project manager to verify work by concrete sub is complete via on-site Superintendent before releasing payment – spoils clean up, forms removed, block-out mistakes repaired, damage from trucks to landscaping/existing paving, etc.
• All subcontractors should be reminded from time to time at weekly on-site meetings no chicken hammers, jack hammers, quickie saws, hammer drills are to be used on the slab without notifying the GC and getting approval before starting work. Depth of work must be confirmed and tendons must be located properly.

After you discover the plumber, electrician, other sub or architect/engineer omitted a sleeve, conduit, anchor, piling, footing, whatever and now have to break the slab to replace, install, remove, repair, etc – what shall I do?

• DO NOT attempt to locate tendons by sight using live end and fasteners from dead end for reference. During the pour the finishers can move tendons 6 or more inches up, down, side to side, etc. from placement pre-pour.
• Call the testing lab and ask them for a tendon locate.
• The price for the technician and the locating instrument will be less than the cost of replacing a broken tendon and a whole lot less than impaling the elevator sub working in the elevator pit when the plumber cuts a tendon moving a floor drain 60 feet away. (No, this did not happen to me but it is possible and you get the point. Work safe. M)

Tendon Repair

Did you attempt to repair plumbing, electrical, sleeves without calling the lab for a locate, find a broken tendon after a sub installed a tub, anchor plate, etc? The slab is over-engineered and depending on the location of the broken tendon a repair may not be required. This is a decision only the PT engineer can make. Prepare an RFI with the location clearly described and marked on a tendon layout diagram from the plans, ask if repair is necessary then send RFI and follow RFI response instructions.

If repair is required coordinate with repair tech and determine what prep work is needed to complete the job.

Check revision date for updates. Work safe.
Marshall

Share this:

• Email

• Print

• More

• Reddit

• Tweet

Like

Loading...

Contact us to discuss your requirements of bulk supply post tension anchor. Our experienced sales team can help you identify the options that best suit your needs.