RAM structural system for PT design 1

[aaronPTeng]

This is aimed at anyone but RAPT your opinion is valued!

I do not use RAM structural system. And Do not know much about it and trying to research it cannot find what I need. I am not looking to buy this software either,

I use a combination of FEA and 2D analysis. What I have found is some common design issues in some projects I am reviewing. To me they seem like someone is pushing there software (in this case RAM) to extreme and ignoring basic design principles. Typical black box what we have all seen discussed on this site plenty of times before! However not to start that again,

I was looking for in site into the methodology behind RAM. Is it based of the American design logic? is it a true FEA software?
Does it allow the idea of a fictional setting to have 1 way slabs between shallow beams which are spanning 1 way and not correctly treat these as banded slabs etc?

Thoughts?

"Structural Engineering is the Art of moulding materials we do not wholly understand into shapes we cannot precisely analyse, so as to withstand forces we cannot really assess, in such a way that the community at large has no reason to suspect the extent of our ignorance." Dr. Dykes, 1976

 

[dcarr82775]

I can't speak to how RAM works. I doubt there is a 3rd party site that breaks it down. My understanding is that it can do FEM depending on the settings used.

But if I understand the scenario you are presenting, it doesn't strike me as unreasonable (depending on span ratios and such of course) to design it as a slab spanning one way between band beams and the band beams also spanning one direction. Just look at the quote at the bottom of your post.

 

[rapt]

Aaron,

RAM is true FEM.

But you can get any answer you want from any software. The problem is understanding what is correct and modelling it that way e.g. I can force RAPT to always give you uncracked deflections and to ignore creep and shrinkage effects so that your deflections are much smaller. But that is not correct so I would not do it! I can also tell it to ignore LL for deflection calculations as the deflection are failing with the LL applied (yes, some tried that one too). That is not how concrete and buildings work so why would I do it? It is not designing, it is cheating/deception. I think that is probably the biggest problem with software today. The fact that some/many engineers think that any answer from software is correct no matter what is modelled. As if the software would not give you an incorrect result! That along with a possible lack of morality (not sure if this is the correct word) in some trying to get the cheapest building possible and twisting the rules to achieve this, regardless of the consequences of an understrength product. This goes further than design. There are many known cases of falsified material certificates to get approval for sub-standard materials. Unfortunately our world seems to be heading in this direction!

I have not seen RAM for many years but based on past experience, the designer can force RAM to give good answers or complete rubbish, as they can with any software or even hand calculations.

In the early days, many of the RAM defaults were based on American PT logic. Average moments for flat slabs, uncracked deflections and multipliers for long term deflections. Mxy moments were/are ignored in design. This is still possible but they now have many more options to produce better designs. Proper long term deflections can be calculated. Column/middle strip design approaches can be used. But the old methods are still possible. I am not sure what the default settings in RAM are these days. So a designer can still produce a good design or a completely unrealistic design. But it all is in the control of the designer. He has to understand what is right and model that way.

For example, with your band beam and slab, I have seen designers use the full slab width as the band beam flange, and include the slab tendons parallel to the band in the design of the band as a T section. So at the negative moment sections where those tendons are near the top and the compression zone is in the bottom of the band beam, the tendons have the effective depth of the band beam. The same thing is done in flat slabs with drop panels with the middle strip tendons. This is/was prevalent in designs from some groups in USA, India, Middle East, Singapore, Malaysia and Indonesia that I know of. The drop panel case was even done that way in an example in the PTI manual in the 1970's. I do not know if it is still in there! It is complete rubbish but unfortunately some people convinced themselves that it was acceptable and others believed them because they were supposed to know what they were talking about. You can do this in RAPT, RAM, Adapt and any software. But why would you if that is not how it actually works? The software user is an engineer and is supposed to use his engineering skills to produce a correct design. Software is a calculation tool. It does what it is told. The engineer has to understand the principles of structures and design and use correct calculation procedures to produce a correct design result. unfortunately, it would appear that we have some who just do not understand engineering and others who will deliberately misuse calculation tools to create unsafe or understrength designs to either win projects or to save themselves money.

And the rest of us have to make sure we keep doing things properly and not fall into the trap of doing it that way because it is the only way we can compete (as I was once told as justification for design this way in Singapore, "everyone else does it so how else can I compete and win work!"!).

 

[aaronPTeng]

Rapt,

Agree with all your comments, unfortunately I had a belief that the standard was higher. But I have just to accept what I am seeing a lot is just poor design.
It is frustrating enough seeing such bad design produced, I could imagine with your role in the industry the further frustration when you are being asked to Taylor software to produce results that people think they want.

It is good to see there are still good designers out there who stick to there guns, There is always clients who want good engineers, the issue is Project managers that want cheap engineers and cheaper buildings.

Much appreciated

enjoy the xmas break all


"Structural Engineering is the Art of moulding materials we do not wholly understand into shapes we cannot precisely analyse, so as to withstand forces we cannot really assess, in such a way that the community at large has no reason to suspect the extent of our ignorance." Dr. Dykes, 1976

 

[slickdeals]

aaronPTeng, if it doesn't involve privacy issues, would you mind posting the specific details of the "bad" designs you are seeing? I would like to rephrase my grad school professor, "Garbage in, Garbage out. Nothing can produce bad results faster than a computer".

 

[asixth]

When I design slabs these days I use both RAM and rapt. That actual design and detailing is done using rapt and I generally use ram to check the strips I have used in rapt and to give an overview of the complete structure to make sure I haven't overlooked any "hotspots" as I like to refer to them.

Architects don't believe in regular and practical grids these days or even lining up the load bearing elements as you rundown the building.

 

[Lion06]

aaronPT-

I use Ram Concept quite often. It uses a true FEA for the analysis, but the engineer defines all of the design strips and the slab type (two way mild, two way PT, one way, beam, etc). The type will determine the way the program relates the forces from the FEA to the code checks for the design. Concept is powerful if used appropriately. It's not as user-friendly as most Ram products, but offers the engineer a lot of control and flexibility.


RAPT-

Just for my own edification - Where do you draw the line as to what tendons you would count toward the band beam? It must be something more than just directly over the web or you couldn't have a PT I beam. Where do you, personally, draw the line and is there any technical literature on this? I'm especially curious, because I have a project that I finished up where I have a full story deep PT wall beam. I am using the floor plates above and below as flanges of an I beam and I'm counting on the PT (banded direction) in the floor slab above and below as part of the PT for the beam (admittedly, not helping with balancing the load, but does help with P/A). The wall is only 12" thick, so the banded cables in the floor slabs are not all within the thickness of the wall (web).

 

[rapt]

Lion06,

Any reinforcement or tendons within the effective flange width.

 

[SethGuthrie]

We are more than happy to help with any RAM Concept questions you might have, even if you are only reviewing someone else's model. Our forum is a good place to post questions,

http://communities.bentley.com/products/structural/structural_analysis___design/f/5932.aspx,

but I do look here occasionally as well.

@rapt, thanks for your reply, yes Ram Concept uses finite element analysis (FEA) and the design is based on the tendons and design strips that the engineer lays out. It's changed a lot since rapt used it, I'm sure, but this much is still true. We feel that a full blown FEA approach is the only approach that can accurately design slabs with complex geometry. One dimensional strip-based approaches are fine for regular layouts and easier to review or hand check I'm sure. The program provides a lot of output in the form of graphics, tables and text-audits, but if you don't have all that information at your disposal it probably does seem like a black box.

BTW, Ram Structural System is another program altogether, though it has a lot of integration with Ram Concept, the title of the thread might be misleading.

 

[rapt]

Slickdeals,

Agreed. But I have been sent justifications accusing RAPT of over design based on code formulae and calculation methods where the input into the code formulae was garbage, so the result was garbage, one was justifying an L/D ratio for an RC one way slab end span of over 40 based on the AS3600 default deflection method! I have seen similar using Eurocode 2 in a presentation lecture on how to apply Eurocode 2! It is not just computer programs that are the problems, it is the lack of understanding of structures and design by SOME who use them and any formula/design methodology in many cases.