How does uplift reinforcement work?
How does uplift reinforcement work?
(OP)
Maybe some of you can help out a young EIT. I am designing metal building footings where the uplift condition far outweighs the compressive force from the column load (in Florida). My dillema is that I do not have any background in how to design the reinforcement for the top mat of the square spread footing for this uplift situation. Common sense told me to size the footing to have enough weight to overcome the manufacturer's given uplift reaction. But, as far as the top mat design, I have some intuitive hunches, but I want to do this right.






RE: How does uplift reinforcement work?
RE: How does uplift reinforcement work?
RE: How does uplift reinforcement work?
RE: How does uplift reinforcement work?
RE: How does uplift reinforcement work?
Helmut Schmidhofer
engcomp@pbq.com.au
http://www.engs-comp.com/
RE: How does uplift reinforcement work?
RE: How does uplift reinforcement work?
RE: How does uplift reinforcement work?
RE: How does uplift reinforcement work?
Is there any point in addressing questions on this forum when the answers are ignored?
Helmut
engcomp@pbq.com.au
http://www.engs-comp.com/
RE: How does uplift reinforcement work?
RE: How does uplift reinforcement work?
As you write, you are on the right track. Since your footing does not rest below grade it would not resist soil weight. I assume from your description that the slab and footing are monolithic. That being the case, a worst case design would be when uplift nearly overcomes the shear resistance of the slab at the perimeter of the footing. Therefore, I would check for dead weight of the footing and a line load equivalent to the shear capacity of the slab around the perimeter of the footing. If that does not result in an excessive top mat of reinforcing, I would use it. To cover your concern about floor cracking, you may design for an ultimate moment 30% higher than ACI 318. This is the means used in ACI 350 for treatment plants to limit crack width. In any case, your reinforcement ratio should not be less than the usual .0033.