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RE: Concrete Tank Design Help

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I generally either treat the wall along with a portion of the slab as an
effective retaining wall or I run a computer model assuming springs under
the base slab. Either way, I consider full applied moment transfer at the
wall to slab connection. I've never attempted a design without continuity of
the reinforcement (i.e., a pinned assumption). 

In order to transfer moment thru the joint at an exterior wall, the outside
bar must be continuous. Since a standard 90-degree hook does not provide a
full splice to the bottom slab bar, you would in effect have a partial
splice - thus cracking would likely occur in the region of the hook, where
full tensile continuity is not present. (A hook might be adequate if a slab
extension is provided and the slab bottom bar is extended far enough to be
developed in tension.) I once considered the possibility that if both the
outside wall bar and the bottom slab bar are terminated with standard hooks
and thus are developed into the joint relative to the inside corner of the
joint, they should be adequate. However, a crack could occur diagonally thru
the outside corner where there is not adequate continuity of the outside
bars; thus, this would not be acceptable. 

The inside wall bar must be hooked for development but does not need to have
a splice length. This is because the inside bar is not transferring tension
to the bottom slab bars but rather to the top slab bars. Thus, the top slab
bars must also have a standard hook at the end or be developed into a slab
extension, i.e. both the top slab bar and the inside wall bar must be
developed past the point of intersection of the slab and wall. 

If you look at recommended rebar detailing at beam-column joints, the beam
bars typically terminate with standard hooks and the column bars continue
thru the joint. Now rotate that view 90-degrees and you have a situation
similar to an interior wall on a slab. The wall dowels should have standard
hooks and the slab bars should be continuous. 


William C. Sherman, PE
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com


> -----Original Message-----
> From: Mark Seifried [mailto:mseifried(--nospam--at)ggjengineers.com]
> Sent: Friday, September 27, 2002 7:11 AM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Concrete Tank Design Help
> 
> 
> My question was a general one for all tank walls: interior, 
> exterior, and
> different loadings. Further questions:
> 
> *What about preventing the transfer of slab moment into the 
> walls due to the
> fixed condition between the wall and slab?
> *Partial fixity cracks with 90d hooks; at what plane in the 
> joint would
> adequate tension development end? It would seem that this 
> point would not
> occur until the bend in the hook, wouldn't this moment 
> dissipate as it has
> traveled through the slab?
> *I have run analysis of structural models with many different 
> degrees of
> fixity at the wall base, what percentage moment transfer 
> could a 90d hook
> pinned joint provide along the base of the wall? Zero?
> 
> Thank you for the response. I was beginning to think my 
> question was too
> easy, but I have looked through many ACI & PCA design guides 
> that have not
> touched on this subject. This list server has given provided 
> tremendous
> knowledge within many areas over the last year, especially 
> since I've only
> been out of school a couple of years.
> Mark Seifried, EIT
 

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