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Re: Top Rebar??

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The fator 1.4 for top bar was initially introduced into ACI building code in the year of 1951 as a reduction factor on bond stress.
Horizontal bar in a wall with multiple layers is definitely "top bar".  The factor of 1.4 reflects effects of multiple layers of horizontal bars in a wall.
You can also refer to ACI 318-83 Commentary 12.2.

Good Luck 
Kim, Young Ho
KOPEC,   Korea   

----- Original Message ----- 
From: <Tom.Hunt(--nospam--at)d-fd.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Sunday, March 18, 2001 9:49 AM
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
> 
> 
> 
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