one way shear in thick foundation raft
one way shear in thick foundation raft
(OP)
Hi guys,
I am designing a building foundation which consists in a thick raft with pedestals around the central core and columns. Do u check one way shear over the entire width of the raft or for every pedestal?
I generally check it over the entire width since that, if it will fail in shear, it will fail over the entire width, I don't see a mode of failure where one part will break and the adjacent one will remain ok !
I am designing a building foundation which consists in a thick raft with pedestals around the central core and columns. Do u check one way shear over the entire width of the raft or for every pedestal?
I generally check it over the entire width since that, if it will fail in shear, it will fail over the entire width, I don't see a mode of failure where one part will break and the adjacent one will remain ok !






RE: one way shear in thick foundation raft
BA
RE: one way shear in thick foundation raft
Why extend this to foundations? Well, it's the same basic structure, just upside down. Right?
Granted, for "raft" foundations, you are not as likely to be controlled by shear as you would be for the much thinner elevated slabs. But, I would still caution against assuming that you can engage the entire width of the slab in shear.
RE: one way shear in thick foundation raft
RE: one way shear in thick foundation raft
section 11.11.1 of ACI 318-08 states that beam action (one way shear) where each critical section to be investigated extends in a plane across the entire width.
That's why one way shear will rarely be critical in flat slabs.
RE: one way shear in thick foundation raft
That's a new section of the code. It wasn't there in the 2005 code that I was looking at. Thanks for pointing that out... star for you.
I should get a new / updated copy of the PCA notes to see if that example I referred to has been updated at all. Because it was pretty clear in the older version of the PCA notes that they believed one-way action should be considered.
RE: one way shear in thick foundation raft
Refer to Page 15 and Page 18.
RE: one way shear in thick foundation raft
RE: one way shear in thick foundation raft
The code requirement in 11.11.1.1 (318-08) was 11.12.1.1 (318-05)
RE: one way shear in thick foundation raft
That’s how I’ve done it (i.e. as the article suggests, on p.15: comparing peak stresses to allowables; which is what I was talking about above as far as stresses go).
Interesting though: the allowable(s) they suggest fall into the range of 2*f’c^0.5 and 1*f’c^0.5. I’ve typically used 0.85*2*f’c^0.5. Perhaps I should re-think that.
RE: one way shear in thick foundation raft