RC slab / plate analysis 2D or 3D analysis 1

[SemiPE]

Hi all. I have been studying the CSI safe program for RC slab/plates. One of the analysis option is to analyze the slab/plate in 2D (meaning only the following is considered: rotation at the two horizontal axis and translation in the vertical axis). I have always thought that RC slab/plates should only be analyzed as a 2D element, if we are considering gravity loads only. I believe that the axial loads on a slab caused by frame action is negligible and thus can be ignored in the analysis and design of the slab/plate.

My question is: when would the 3D analysis be useful? does SAFE wants us to consider the axial loads?

 

[asixth]

With the ever creative and often impractical world of the architect sometimes for whatever reason a slab may be subject to in-plane stresses from a sloping column or whatever so in those circumstances the in-plane tensile forces need to be considered if they arise.

Many people are going towards the way of plate elements for the analysis of floor slabs but design-wise strips need to be considered. This is for strength, service and deflection calcs. I don't know what theory some of these FE-RC programs are applying to calculate out deflections.

If you type Wood Armer, Mxy into the search tab above some good threads so come up. Here's one that had a good a lively discussion thread588-259325

 

[jsha811]

It looks to me that in your 2D anlysis, the membrane behavior of the slab is ignored which is conservative. The membrane behavior does help to take even the gravity load.In think in SAP2000 which is the same family as SAFE,you can specify different thickness for slab bending and membrane behavior. If you take a look at the program manual, it may give you some idea of what the program is doing there.

Moment curvature analysis,reinforced concrete column design and prestressed concrete pile design at

http://www.structurexpress.com

 

[SemiPE]

@ asixth - it seems like innovation (CAD software, computer programs, etc.) is a double edge sword. More fun for the architect more nightmares for the engineers. I imagine if a slab is subjected to such forces it has to be in some concentrated areas of the slab (and not acting on the whole cross-section of the slab) then the slab will act like a wall where it has axial forces and bending moments. Do you have any good literature or reference on this subject matter? using hand calculations. I would like to go manual first before going to automatic.