Floor area vs Static for reactions
Floor area vs Static for reactions
(OP)
I would like to know which method do you use when determining reactions on transfer slabs, I've been told to use static if you have a concrete framed structure (multi-storey building) and use floor area when the slabs are supported by walls.
I usually get higher reactions when using floor area but when using static the loads are distributed differently and I get lower reactions at transfer columns,I know the reaction would be lower due to the slab deflecting, hence the load is distributed elsewhere. I then usually go for the higher reaction to design the slab.
I usually get higher reactions when using floor area but when using static the loads are distributed differently and I get lower reactions at transfer columns,I know the reaction would be lower due to the slab deflecting, hence the load is distributed elsewhere. I then usually go for the higher reaction to design the slab.






RE: Floor area vs Static for reactions
RE: Floor area vs Static for reactions
Static linear: basically solving equations of equilibrium
I guess my question is the reactions from the columns above is only realized when the slab below cracks (hence lower reaction), effectively if you take the extreme case and remove the surrounding supports the column would just hang and therefore there would be zero reaction.
I hope this makes sense
RE: Floor area vs Static for reactions
Just to be conservative, I would not account for the deflection of the supporting slab/beam/girder.
I would track the load using statics however, and use the higher of that and the trib area load.
RE: Floor area vs Static for reactions
RE: Floor area vs Static for reactions
Additionally, EIcracked of the supporting member is not the easiest value to come up with (if you want an accurate representation of the true behavior), and this value is what directly affects the deflection, and consequently, the load on the column.
RE: Floor area vs Static for reactions
You are very right in realising that the deflection of the transfer beam can effect the loads from the beam over.
I would agree with structural EIT in that I would not use this to reduce the imposed loads.
One thing you need to consider, however, is the redistribution of moments resulting from the deflection of the supports. If a given support deflects more than the surrounding supports then this will increase the positive elastic moment values at that support (possibly negating the negative moment from continuity) if the support deflects less than the surrounding supports then this will increase the negative moments.
I would always try and design transfer nbeams to as stringent a deflection criteria as possible at least L/500 but preferably L/1000 or better. This will help to reduce the effects of sagging supports noted above.
RE: Floor area vs Static for reactions
When I design a tranfer slab/beam I do following; compare reaction floor analysis (RFA) and Reaction Static analysis (RSA) on transfer slab.
I also increase the tranfer slab stiffness by 4 times and use static analysis and compare with RFA. The results seem more accurate this way. what do you think?
RE: Floor area vs Static for reactions
I am not familiar with your terminology, is there a particular publication that outlines these methods?
RE: Floor area vs Static for reactions
RSA = reactions by Static analysis
it just my way of know which type of analysis I used, I put RSA or RFA at end of file name.
RE: Floor area vs Static for reactions
What you propose sounds reasonable.