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CWEngineer (Civil/Environmental) (OP)
7 Jan 08 18:05
Do you guys/girls know where I can find a statement similiar to the following:  

"For Top Bar, that is horizontal reinforcement having more than 12 in. of concrete cast below the bars, 1.4 times the basic ld must be used.  An accumulation of air and water that rises beneath such bars become entrapped on their underside."

I obtained this statement from a previous project, but I have not been able to locate this statement in my reference.

Thanks
CWEngineer (Civil/Environmental) (OP)
7 Jan 08 18:18
The reason I am trying to obtain a reference with an explanation is to clarify what reinforcement would be considered "Top Bar" and "Other Bar" when determining Lap Splices for a horizontal concrete slab, slope concrete slab and vertical wall.

THANKS
Taro (Structural)
7 Jan 08 18:49
ACI 318 Section 12.2.4.  The top bar factor changed to 1.3 several code cycles ago.
CWEngineer (Civil/Environmental) (OP)
7 Jan 08 19:35
I am also trying to verify and clarify the following:

1.  Is the concept of "Top Bar" and "Other Bar" only used when determining the LAP Splice in a horizontal concrete slab and beam?
2.  Can the concept of "Top Bar" and "Other Bar" be used when determining the LAP Splice in a sloped concrete slab and beam?
3.  Due to the construction process of a vertical wall, is "Other Bar" applicable to all bars (vertical flexure, vertical temperature, and horizontal tempeature/shrinkage bars)?
4.  How would you determine if a bar is a "Top Bar" or "Other Bar" for concrete shapes other than horizontal slabs such as a key?

Really Appreciate your Help.
   
msucog (Civil/Environmental)
7 Jan 08 20:22
as a rule, i go with the most conservative unless it is specifically noted on the plans. field inspectors should not be left to have and determine that. and if i were designing a structure, i'd prefer to know that there's no ambiguity as to what it should be.
Lion06 (Structural)
7 Jan 08 20:25
any bar that has more than 12" of FRESH concrete cast beneath it (and is horizontal) is a "top" bar.
"top" bar does not apply to vertical bars.  
"top" bars can be in any member - slabs (only very thick ones), beams, girders, walls, footings.
JAE (Structural)
7 Jan 08 22:08
I'd add that I would consider a sloped bar with 12" below it a "top" bar as well.

KCRatnayake (Structural)
4 Feb 08 1:10
JAE, StructuralEIT,
If individual pad footing has only one r/f mesh at the bottom, will you call it a top bar?

KC
Lion06 (Structural)
4 Feb 08 8:20
clefcon-
If there is more than 12" of fresh concrete cast below it, then absolutely yes.
JAE (Structural)
4 Feb 08 10:01
Yes - the key is the 12" of fresh concrete below the bar, not what it is used for.

KCRatnayake (Structural)
4 Feb 08 10:43
JAE, StructuralEIT,
My question was that bottem r/f mesh has only 2" thick concrete below it as the cover. You still call it a "Top Bar"? Sorry for bothering you too much.

KC
JAE (Structural)
4 Feb 08 12:20
Just ask yourself, "Does the reinforcing have 12" or more of fresh concrete below it"?  If it does, then you MUST use the factor to increase your required lap lengths for splices.

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