Lap splices for #14 rebars

[DST148]

ACI 318-11, section 12.14.2.1 does not permit lap splices for bars larger than #11. The commentary says it's because of lack of experimental data on lap splices for #14 and #18 bars.
We are designing a pile supported mat, 5'-6" thick with a clear cover of 9" to the bottom bars.
Are splices for #14 bars permitted by other (country) codes in situations where clear cover to rebars is in the range of 8" to 9"?

 

[hokie66]

The Australian Code, AS3600-2009, specifies that "Lapped splices shall not be used for bars in compression or tension with diameter larger than 40 mm." I am relatively certain that provision assumes concrete elements with 'normal' cover, and I wouldn't consider 9" cover to be normal. Why so much cover in your mat?

 

[DST148]

As mentioned in my OP, the mat is supported on piles. The pile embedment is 6" and the bottom bars shall be placed minimum 3" above the top of the piles
and therefore a clear cover of 9".

 

[TXStructural]

There is experimental work underway now, but I would expect most laps to continue to be restricted for most uses, owing to the large splitting forces involved. This pronounced with larger bars because of the large force in a pair of these bars. Couplers are expensive, but when you get to these large sizes, a coupler frequently is the only practical method, due to long development length and the space taken by a pair of bars in the area of the splice.

 

[hokie66]

Pile embedment of 6" and cover over the piles of 3" generally does not add up to 9" cover overall. A more normal detail would be to pass the main reinforcement beside the pile, and add some bars just over the pile.

 

[JAE]

#14 are very large bars to be using in a 5'-6" cap. Keep in mind that if you are depending on the bars to resist shear forces across the pile "cone" you have to develop them past the cone plane.
And for positive bending you typically like to have the bottom bars extend far enough to be effective in tension due to mat arching action (deep beam theory).

 

[DST148]

Thanks hokie66, TXStructural, and JAE for your input.
I have attached a file showing calculations for development length for #14 rebar for the project. The edge of the mat from the centre line of piles is 4'-0" minimum. Although the sketch shows overlaps @ 12" o.c., alternate bars could be spliced, thus increasing the c/c distance of the bars being developed to 24" o.c. (staggering of splices)
The bars are being developed on either side of a given section. The overlap shall be 2 * development length = 2 * 38" = 76" = 6'-4". It does not seem to be too large theoretically.

ACI 318 -05, R7.6.6.4 - Bundling of bars - Commentary : A limitation that bars larger than #11 not be bundled in beams or girders is a practical limit for application to building size members. The Standard Specifications for Highway Bridges permits two-bar bundles for #14 and #18 bars in bridge girders. I am not familiar with bridge design. Does the standard cited above permit bundling of #14 rebars using splices?

 

[DST148]

I Googled AASHTO Specifications for tension lap splices. AASHTO does not permit lap splices for #14 and #18 rebars even when the clear cover > 3".
Thank you all once again.

 

[a7x1984]

Can't you achieve the same As(req) with smaller bars/tighter spacing? If you can't, you are going to have to use mechanical splices or weld per AWS D1.1. Maybe welding would be cheaper if they already have somebody onsite for something else? I do agree the size seems awful large for such a small cap. Your link didn't work for me.

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