Designing P/T podium slab 2

[kushal2944]

I have a four story wood-frame structure over a podium (transfer) slab. We first designed it with conventional reinforcement but now my supervisor wants to check if we can come up with a post tensioned slab option.
What softwares are there to design this kind of elevated P/T slab with irregular loading from wood frame above? Please suggest.

Thanks,
Kushal

 

[KootK]

Adapt
Ram Concept
CSI SAFE
RAPT
Ken Bondy has something I think...

Lot's more I'm sure.


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.

 

[kushal2944]

KootK,
Thanks. Have you (or your office) used them personally? In your experience (or your colleague's) do you prefer one over another? (In the sense that which is user friendly, which has less limitations, and which gives better results.)

 

[mike20793]

I've started using Ram a lot recently and I like it, so for me it's Ram Concept over others, then ADAPT. Unforturnately, I haven't used the others for PT design, but I hear good things about RAPT.

 

[MrHershey]

Only issue with RAM products if you're more than a couple person office and looking to purchase is pay close attention to your licensing and who's using it. Once you've downloaded their software they will let as many people from your organization in as want to, won't cap it to however many you've paid for, won't give any indication that you're going over your purchased amount, don't even give you the option of seeing who is in any of the programs at any given time, and then will send you a bill at the end of the quarter (usually higher than your yearly rate) for any usage over your purchased amount and then try to negotiate with you to buy more licenses. While RAM Concept is powerful and perhaps the best PT software out there right now, if I were starting from scratch I'd think of trying out one of the other ones first just because of what RAM is doing with their licensing right now.

 

[Trenno]

Another vote for RAM Concept. Takes a while to understand the in's and out's of the program though.

Very powerful indeed.

 

[KootK]

I've used Adapt, RAM, and SAFE. It's RAM for me by a wide margin. The quick model setup makes it a very productive tool.

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.

 

[rapt]

kushal2944

Your decision should be based in part on the experience you have in PT design. If a beginner, you should not be using Finite Element design software. This software requires a high level of understanding of and experience in the layout and design of PT floor systems.

I know there will be people who have had no experience in the design of PT or other specialist areas who will say that they have done this successfully. In my opinion they do not understand the concept of being an engineer and the tools that they use and probably do not understand if what they have produced was successful or not. I have seen completely incompetent designs produced in finite element software simply because the designers did not understand both PT design and what the software was doing for them and therefore how to use and interpret it properly (unfortunately one of these collapsed during construction resulting in one death).

 

[Trenno]

RAPT, do you have a link or any details relating to that collapse?

 

[rapt]

Trenno,

No sorry. It was in Dubai several years ago and an area of one slab collapsed when the floor above was being poured. I looked at it for an engineer involved in checking it after the collapse. It was very obvious from the drawings why the collapse occurred. An experienced designer should have seen it straight away but "averaging" of effects in an FEM computer program gave results that said everything was ok.

Too bad there was basically no tendons or reinforcement in either direction over the top of one very un-important column within the punching zone of the column!

Looking at the overall layout for the whole design showed how badly someone can distribute tendons and the computer program still can say all is ok! The layout in the 2 directions was absolutely stupid and very inconsistent.

 

[kushal2944]

Thank you everybody for your input. More are welcome to give their views.

RAPT I get what you mean. But those kind of people are everywhere, not just in design of PT.
Anyway, I have had introduction to PT during undergrad and I took another course during my Masters. So I am familiar with PT. And I have had courses on Finite element and have used FEM software for other purposes.
But NO, I do not have any real world experience in designing PT or using any FEM to model it. So I guess I am a beginner with good backgrounds. I will definitely get help from an experienced engineer. Meanwhile I have to decide on what software we should be buying. The irregular loading because of wood framed floors above tempt me to get a 3D software.

 

[mike20793]

I hate to say it, but there are way too many nuances in the design of a podium slab for a first time designer to take on alone, regardless of what classes you took in school. This design should be the sole responsibility of your supervising engineer.

 

[rapt]

Kushal,

I have never seen a course on PT that teaches how to approach a design for a complicated slab or how to lay out the PT or even how to model it in FEM (or anywhere else) and interpret the design results correctly. If such a course exists then great, but in my experience the only way to do it is practice and FEM is not the place to start learning and practicing.

 

[KootK]

I don't agree with all of the caution expressed here. OP has had as much relevant formal education in PT and FEM as the rest of us. And he's having his work reviewed by a senior engineer. And he's already experienced with mildly reinforced slabs. What more could we ask? In this day and age, are we really expecting OP to hand calc his way through a few complicated floor plates before he uses software? We know full well that his employer won't be paying for that.

I've been mentored by several experienced PT engineers and it was great. In retrospect, however, I didn't pick up anything earth shattering from them that wasn't also available out there in the literature as well. Shrinkage, restraint, balancing, ductility, durability, vibration, deflection, punching shear... The list isn't really much longer than it would be for a steel roof or even a wood deck. PT's neat stuff but you don't have to be bloody Voldemort to pull it off.

Part of being an engineer is being bold enough to apply your knowledge to new technologies that you were previously unfamiliar with. Sometime has to be everybody's first time. Sometime occasionaly has to be the first time. I think that we'd serve OP better by discussing the nuances with him rather than trying to scare him off of using software.

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.

 

[Guest262653]

@KootK

Great, great post. Thank you!

 

[Ingenuity]

Just make sure you don't deduct the balanced load effects from the factored ultimate demand moments

I see an aweful lot of screwed up PT structures. Both on the drawing board and 10+ years after they are built. I recall one structure from the late 90's where the engineer detailed 72 tendons in a band. Our quick hand calc suggested 24. When asked how he arrived at 72 tendons his response was "we did a FEM analysis and that is what was required". The structure was built with 24 tendons per band.

From that time in the late 90's until present, whilst the FEM software has got "better" (aka more user friendly etc) it is my opinion that undergrads finish their degrees with less prestressed concrete experience than when I graduated in the 80's.

If you speak with engineers who are employed by PT companies, oftrn they will share some horror stories with you of PT floor systems that have to be redesigned to make "work".

Inguess reduced design fees for consultants across the globe it is understandable that software plays an important role in cost effective design fees, but only in the hands of experienced users.

 

[KootK]

Just make sure you don't deduct the balanced load effects from the factored ultimate demand moments

Or, if you do, be savvy enough with the fundamental mechanics to adjust the ULS bending strength calculation accordingly.

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.

 

[rowingengineer]

WE do both a FEA model and a band model, even with experience we find this is the best way to make sure you have most your eggs in basket.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[Trenno]

Agree with KootK here. But you can't just let young engineers loose with this kind of software. They need to know the basics and be inquisitive enough to research each and every input/output/result to prove to themselves it's a sensible design.

Agree with rowingengineer too - when I design PT, I usually start with taking a few RAPT (2D) runs to get a feel for how the design is working and my tendon profiles. Then I feed information from the 2D runs into my 3D RAM Concept model.

What I will say however - there are some unique geometry and transfer loading arrangements that are almost impossible to design using hand calcs and 2D runs. This is where 3D models come in handy.

Good saying from one of my seniors: "if it looks wrong, it probably is."

 

[rapt]

RE
Like your latest footnote! We are not trying to compete with the universe on this one. We write our software for experienced engineers (as you know) and hope the idiots will find it too expensive and too hard to use and buy something cheaper and more idiot friendly!

Kootk,
It is a problem in life (and engineering) that we think we know what we are doing and do not find out what we do not know until it comes back to bite us. In Engineering we hope that happens before the mistake is built when someone who actually knows more than us lets us know and we listen to him, rather than afterwards and we have to pick up the pieces.

Since the advent of more and more complex software, unfortunately we are finding less people able to assist with the better result scenario and many more examples of the humpty dumpty syndrome.

When we leave university we think we know everything. In the next couple of years we find out that we knew nothing when we left university. By the time we get nearer retirement, we realize we still knew stuff all after the first 2 years. By the time we retire, we probably know enough to be good engineers. Unfortunately it is too, late by then!

And no one will listen to the old timers because they are all too old to understand the modern world we now live in.