which one to use for design beam supporting a slab, tributary area load or FEM analysised forces?
which one to use for design beam supporting a slab, tributary area load or FEM analysised forces?
(OP)
I am confused about the above case as FEM results and manual tributary area method gives different results especially in one way slab. Is it ok to design slabs and beams modeled together?( or else design beams seperately with tributary area loads?)
what is the best modelling approach?
Your replies would highly appreciated.
thanks
what is the best modelling approach?
Your replies would highly appreciated.
thanks
RE: which one to use for design beam supporting a slab, tributary area load or FEM analysised forces?
Cheers
Greg Locock
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RE: which one to use for design beam supporting a slab, tributary area load or FEM analysised forces?
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.
RE: which one to use for design beam supporting a slab, tributary area load or FEM analysised forces?
RE: which one to use for design beam supporting a slab, tributary area load or FEM analysised forces?
- staging of construction - It basically models the building assuming it was fully supported until it is all constructed and then all of the temporary supports are removed.
- it does not consider inelastic effects, cracking etc and redistribution resulting from it.
- it does not consider creep and shrinkage effects.
The problem with tributary areas is getting them right and allowing for the correct areas and any redistribution that happens due to axial shortening of supports and other effects.
I think the answer is normally somewhere between the two, but conservatively I would always use the worst of the 2.
Transfer beams are the most important member in the structure, it is logical to give them a higher factor of safety anyway. If you consider Robustness in your design, normally the only way to justify a transfer beam is to increase its factor of safety even further!
RE: which one to use for design beam supporting a slab, tributary area load or FEM analysised forces?
I agree to the Rapt's point. But I'm curious about very complex structures where the manual calculations are very tedious or difficult to carry out, how we are going to compare the results like that.?
RE: which one to use for design beam supporting a slab, tributary area load or FEM analysised forces?
If you were able to set up your FEM model to not allow axial shortening in the supporting members and not allow deflection in your transfer beams, then I would think that you should get an even more accurate version of the tributary area approach. P.S. this method is trademarked by me so anyone who has never thought of it before and wants to use it, please send donations!
RE: which one to use for design beam supporting a slab, tributary area load or FEM analysised forces?
1. Fea
2. Rapt (trib method with excel load take down)
3. Rules of thumb
If any of these fail to meet a +/- 15% rule we spend a few hours figuring out why.
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