Use and Abuse of "Redistribution"
Use and Abuse of "Redistribution"
(OP)
I have a feeling that "redistribution" is taken to advantage blindly by engineers like me.
My opinion:
Redistribution means you have a load carrying system, which fails to perform at some locations, and immediately transforms itself into a different load carrying system(sort of an alternate load carrying mechanism).
If the load carrying capacity of the alternate mechanism can be ascertained for sure, then one can take advantage of "redistribution". Otherwise NOT.
Anyone wants to spill up some experience and insights on this too theoretical one?
respects
IJR
My opinion:
Redistribution means you have a load carrying system, which fails to perform at some locations, and immediately transforms itself into a different load carrying system(sort of an alternate load carrying mechanism).
If the load carrying capacity of the alternate mechanism can be ascertained for sure, then one can take advantage of "redistribution". Otherwise NOT.
Anyone wants to spill up some experience and insights on this too theoretical one?
respects
IJR





RE: Use and Abuse of "Redistribution"
RE: Use and Abuse of "Redistribution"
I myself many times (maybe in 1/4th of the buildings I have had such structural respansability in design) have lessed end moments on top spans of frames, when I was young most surely at least more than 1 time to exceed the stated allowable redistributrion in the code. In some cases (not specifically those I have named necessarily, for I don't remember the particular practice at the point) some minor crack in the attached partition masonries showed, and I assume where the beam more disengages the column (due to lower reinforcement at the corner) the "horizontal" crack must have had to appear. This is difficult to say due to the typical joint between column and beam that resembles sometimes a crack where is not. You can observe it at lower inner floors. In any case the bad effects of this my practice for some cases have been to all practical effects nil. I have tracked far more deffects in such corners related to the elongation of the solidary roof under sunheat, again to no reclamations in 400000 m2 built.
Respect redistribution 2 way, I have had the opportunity of calculate the same slab with and without a sizeable hole, for almost the same stresses.
There's one quote on one ACI book on test on one decomissioned slab-bridge on doubts of its bearing load ability that had to be demolished because the test that was being made for information purposes attained 20 times the required load and still failed to fall! And was being decomissioned due to doubts on bearing the loads! Monlithic RC redistributes very well.
My opinion, on experience and what exposed is that for any safety purposes normally if you have a failure where some redistribuition has been made, some other more relevant factor must be in place.
RE: Use and Abuse of "Redistribution"
RE: Use and Abuse of "Redistribution"
Thus all watertight structures designed in complience with ACI 350 and utilizing WSD method do not employ moment redistribution
ACI 318 recomends to use additional overload factors for Ultimate Strength Design Method for Watertight Structures but is silent on the issue of negative moment redistribution in continuous members.
If negative moment redistribution is allowed both methods will yield widely incompatible results. However overload coefficients were introduced to make both methods compatible .
Does anybody knows the answer?