ACI-117 rebar placement tolerances

[boffintech]

Ties in columns and stirrups in beams are required to be perpendicular to the member. The tolerance for this is stated where???

Occasionally column ties and beam stirrups are fabricated too large in one dimension and as a result can only be placed by "racking". Is there anything in chpt 2.2 of ACI-117 that prohibits this practice. Or anything in chpt 7 of ACI-318?

Reason I ask, have a 2' thick shearwall with #4 cross-ties. Cover should be 1 1/2" each side. Looks like they were fabbed 1'10" which will result in 1" cover each side. A little racking ought to get the correct but what's the limit on this kind of thing?

 

[Taro]

Is this an interior exposure? I would rather have the cross-ties level and reduce the cover by 1/2". The purpose of the ties is to provide confinement to the longitudinal bars and concrete core. The ties cannot perform effectively if they are sloped. After the cover spalls off, the ties can slip into the horizontal position, the core will expand and the strength will drop.

 

[boffintech]

Exterior exposure (bottom level of parking deck).

 

[boffintech]

Oh, forgot to mention that the horizontals are # 6 at 12".

The cover on the #6 is 2" each side. So the cover on the #11 vert is actually about 2 1/2" or out-to-out about 19". That makes the cross-tie about 2" too long.

 

[msucog]

i don't recall exactly but if it were me, i'd consider two avenues to resolve the issue while trying to double check ACI: 1. have the contractor send the things back to the fabricator since it was the fabricator's mistake. of course, this causes headaches to everyone for something that might be able to be resolved in the field. 2. get the 1 1/2" to the backfilled side, keep the stirrups as level as possible with just a slight slope that is "typical" to construction and then have the smaller clearence to the inside since i would think that you could make it work based on the info you provided. the contractor will need to do some fine tuning since the stirrups are likely not all perfect dimensions and may have a few that have a leg sticking out too far. realistically, the intersection where the stirrup opens could be taken care of pretty easily so that only leaves one other corner that would stick out too far. with a little extra headache during placement, it should work without having a situation that is unacceptable. HOWEVER, the structural engineer may want to put their own eyes on it since it is their call. if they're not happy, then send the things back.

typically, the contractor would just pull out the sledge hammers and pipe benders and the engineer likely would not know of or see such a "fix". i doubt the inspector would see it as long as the contractor didn't do anything extreme. and you could also pull at the midlength of two side to the effectively make the thing short in one dimension.

 

[msucog]

out of curiousity since i don't know the answer about level tolerances for stirrups, i quickly checked out 117 and 318. the stirrups are out on the manufacturing dimension allowance i saw in aci 117. for clearances, you've obviously got different clearances depending on the situation and member type. also, to make sure i didn't cause confusion, in my last post where i say "backfilled side" i was referring to the exterior side and not that the wall was backfilled.

i don't have a definitive answer after looking. i suppose you could always take another look at the situation using an equation for sloping stirrups to see what kind of difference it makes in the strength. my personal opinion is that you're not building a watch and if the stirrups are generally level (say within 1-2" of level for 2' depth), then i likely would not raise the red flag. if it looks ugly and appears completely out of whack, i'd start pulling references and contacting the structural engineer to see what they want. as i said before for your situation, an experienced contractor would make it work without it being obvious (whether this is considered right or wrong). if the eor is severely concerned, the contractor should send the stirrups back and get the more correct ones.

 

[miecz]

When used for shear reinforcement, ACI 11.5.6.4 allows stirrups to be inclined.

 

[DWHA]

I would try and talk the contractor into making the wall 1" thinker at his expense.

 

[Taro]

miecz, cross-ties in a shear wall are not shear reinforcement so that does not apply.

 

[henri2]

Boffintech,

If the wall is also designed to withstand out of plane bending forces, then the effective depth d is greater than 8 in. Check ACI 318-05 Sec 2.2 for definition of effective depth of section. The notation d is also explained in Sec 2.1. For this particular situation, consider it as the distance of the centroid (center) of the verts from the far face of the wall.

Based on ACI 318 Sec 7.5.2.1, the tolerance used to determine minimum acceptable cover is -1/2 in. For a specified cover of 1-1/2 in , the min acceptable cover is equal to 1 in.

 

[hokie66]

I agree with Taro that confinement ties in a shear wall need to placed perpendicular to the bars which they are confining, in this case the #11 verticals. The ties which have been fabricated 2" too long are unusable unless the wall is thickened to suit.