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RE: Top Rebar??

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The term top bar kind of went out of style in ACI 318 when the alpha factors
were introduced (Re: ACI 318-95 and 99 sect 12.2.4).  And you are correct in
the concept of the trapped air and water under the rebar.  The most recent
research for the alpha factors was done at the University of Texas and is
cited in the ACI 318.

Harold O. Sprague

> -----Original Message-----
> From:	Tom.Hunt(--nospam--at) [SMTP:Tom.Hunt(--nospam--at)]
> Sent:	Saturday, March 17, 2001 6:49 PM
> To:	seaint(--nospam--at)
> Subject:	Top Rebar??
> Speaking of seawater structures, I have received an interesting plan check
> comment.  We have designed a rather large double cell box culvert with
> good
> size rebar vertically and horizontally in the walls due to a significant
> surcharge from a nearby railroad.  The plan checker has requested that we
> consider all HORIZONTAL wall bars as top bars in designing our splices.
> Now I know that the code reads that top bars are those with 12 inches or
> more of fresh concrete below but I have only used this in slabs and beams.
> I reviewed several texts and did not find anything definitive.
> When I was in school I was told that the top bar reduction was due to the
> possible accumulation of micro air bubbles rising to the surface.  Would
> this apply to all the horizontal bars in a 2 foot thick by 16 feet tall
> wall??  I have been given widely different opinions on both sides of the
> issue.
> Thomas Hunt, S.E.
> Duke/Fluor Daniel