Lapping of Two Rebars with Different Spacing

[CWEngineer]

I am reviewing rebar detail drawings and noticed that two bars that are lapped have differnt spacing. There is a #5@12 lapped with a #6@18.

From the 12" and 18" spacing, every other 4 bars of the #5 will be be in contact with the #6 bar AND every other 3 bars of the #6 bar will be in contact with the #5 bar.

Is lapped bars with different spacing a discrepancy or is this allowed? I am looking at the ACI code to determine if this is allowed but I have not found a section allowing this yet. Appreicate if someone can help me clarify this.

Thanks

 

[civilperson]

Non contact lapped bars are allowed and specified for spacing in 12.14.2.3.

 

[shin25]

The link below should give you some insight-

http://www.eng-tips.com/viewthread.cfm?qid=173097&page=1

 

[boffintech]

Does 12.14.2.3 apply to vertical bars in walls, shearwalls, and columns?

 

[WillisV]

Depends what they are being used for...as long as its flexural tension I would say yes.

 

[boffintech]

WillisV, How would an inspector decipher this in the field from just the structural drawings?

I ask because CRSI distributes a DVD in which they show a wall with dowels off-set from the vertical bars and they cite as reference 12.14.2.2.3 that this is OK and imply that this is true is all cases. How do I know in the field if this applies.

Also, in reference to the tread

http://www.eng-tips.com/viewthread.cfm?qid=173097&page=1

I have read that ACI-318-08 will be changed to read:
"Tension lap splice length for two different size reinforcing bars is defined as the larger of the tension development length of the larger bar and the tension lap splice length of the smaller bar."

 

[WillisV]

Good question - I would assume the only way to really know if it was in doubt would be to call the structural engineer. I think this provision would probably be applicable in most typical wall and beam cases though. The only cases that I can think I personally would really not feel comfortable with it would be cases that I (and the code) would want a full mechanical splice in lieu of a contact splice anyway (such as in the tension tie of a deep beam).

 

[msucog]

if two different size bars are lapped, you use the larger bar lap length (i never see tension or compression called out on the plans so i use tension lap length by default unless it's something special then i'd call the designer). based on your description, i'm picturing something like #6 dowels sticking out of a footing at 18"o.c. with #5 vertical bars in the stem at 12"o.c...is this a correct picture?

if this is correct, what the heck do the intermediate #5's tie in to (between the #6's)?...given, the section boffintech mentions says 6" noncontact splices are okay but as a matter of field practicality, could it not just be #5's at 12"o.c. everywhere? (if i recall my rebar areas correctly, it should be okay...actual design might require #6's for other reasons i suppose). my point: unfortunately contractors and their people are often "blowing and going", perhaps non-english speaking/reading here in the u.s., and stubborn ("been doin' it like this 30 years"). while this is not necessarily the problem for the designer, it does impact them because they want it built like they draw it. so for the sake of protecting their own butts (and getting what they want), it seems logical to me to "dumb it down" for the contractor. hopefully, as special inspections become required more, there will be "better" (perhaps "more" is a better term) oversight of the field work. that being said, the designer should be able to get whatever they draw but it doesn't always work out that easy in the field.

if i were looking at this in the field, i'd look for exactly what the drawings said, #5 @ 12" and #6 @ 18" with a #6 lap length. i wouldn't call the structural if the contractor had in the field what the plans showed. however, i'm willing to bet they'd screw up the lap length since they'd use either the #5 lap length or 2' (i don't know why 2' but that seems like a good round number i see contractors using all the time for no apparent reason--contractor:"we always just use 24 inches"---my response: "well you see this little table here with lap lengths? yep, that's what i'm looking for.")