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.
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
BA
RE: Design of Irregular Panels in RAPT
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
RE: Design of Irregular Panels in RAPT