×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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!
  • Students Click Here

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

Posting Guidelines

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

Students Click Here

Jobs

Design of Irregular Panels in RAPT

Design of Irregular Panels in RAPT

Design of Irregular Panels in RAPT

(OP)
Dear Rapt,

How to justify the design of irregular panels using the rapt software. some people are arguing design of irregular grids should be done by using only fem software only like adapt and ram.

RE: Design of Irregular Panels in RAPT

Irregular panels have been designed successfully by hand methods for many years, so I would disagree with "some people".

BA

RE: Design of Irregular Panels in RAPT

As long as you can define logical support strips and contribution slab/load widths, to fully cover the floor slab and get the loads to the supports and then to the foundations, there is no reason why you cannot analyse and design irregular floor slabs in RAPT. We used to do it without computers as BA suggested and have been doing it in RAPT for 30 years. The main thing as in any design is that you have to be consistent in the design across the slab and make sure the necessary load paths are provided to get the loads to the foundations!

Many designers doing the same designs in FEM software will reduce the design to simplifications (such as the ACI average panel design for PT flat slabs) which completely negate the benefits of FEM and quite often can give very misleading and often very incorrect results. It all depends on how the designers uses and interprets the data from the software. It is like using FEM to provide a yield line result. Not possible but some try.

I know a lot of designers will use a combination of RAM and RAPT on complicated slabs, because RAPT makes it a lot easier to interpret and iterate a design for a specific area of the slab. And also to do more detailed checks on deflections etc.

The other thing you have to remember is that an FEM solution is assuming everything is detailed as per the FEM analysis, and the concrete does not crack! Reinforcing is normally not laid out exactly as per the FEM results, so redistribution is required and this changes the analysis from the FEM analysis. The more the reinforcing pattern varies from the FEM analysis, the more redistribution is required. Cracking happens, and this changes the analysis from the FEM analysis.

For ACI flat slab using average moment design, I personally think it should never be done on FEM as you are using an FEM distribution of effects to essentially do a quasi (read fudged) yield line design requiring enormous amounts of redistribution. For complicated support layouts in this case, the FEM assumed distribution of loads can be completely different to that used in detailing the prestress in the two directions, so you end up with a PT layout that really is no match to the FEM results that you are using to design to.

Creep, shrinkage and restraint happen and these is not modelled fully in the analysis.

And finally there are so many numbers in the FEM result, many designers just accept it without optimizing design in specific areas or even look at the background to the results.

None of this is criticising FEM software, more how it is used.

Other people have reported "unusual/unexpected/unexplainable" results from FEM software when they have looked into it in detail. No one is sure how the FEM has been able to come up with the numbers it has to explain the solution it has given. These effects tend to occur when there are stiffer elements such as beams or band beams in the floor. And the results can be worrying. Many experienced PT designers in Europe, Asia and Australia will not use FEM as soon as there are band beams or beams involved in a slab.

This just makes it important that the designer have sufficient experience to know when there is something wrong and when and how to check it out, often using 2D software.

PS in future RAPT support questions should be directed direct to me at Raptsoftware! Not on Eng-tips!

RE: Design of Irregular Panels in RAPT

(OP)
Thank you BAretired .

RE: Design of Irregular Panels in RAPT

(OP)
Thank you rapt and well noted regarding support questions i will send quires to support in future.

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!


Resources