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Top Rebar??

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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

Thomas Hunt, S.E.
Duke/Fluor Daniel