Pile Cap Reinforcing 1

[dylansdad]

I have been consulted to review the following situation. Here is what I have. A square pile cap 8'-6" x 8'-6". The piles are on a 4'-6" square pattern with 2' from pile to edge and 18" round concrete piles extending 4" into the cap. The pile cap is 3' thick with reinforcing 2" clear above the top of the piles. Apparently, the bar detailer did not pick up on the 180 degree hooks for the reinforcing which is 9-#8 ea. way. These caps were poured with this "straight" reinforcing. I have a set of plans and am just beginning to chase down the loads that are involved. W14 steel columns bear directly (grout) on top of the cap. I am at a loss as to how this slipped through the cracks, and the several sets of eyes that should have caught this. Is there any remedy other than tearing these out and replacing? I should add that 6-#8 and 1-#9 extend from the piles to near the top of the cap.

 

[J1D]

Is the column at the center of the pile group?

If it is, the direction of the tie is not perpendicular to conrete edge. More room is availble for the development length.

In addition, I would check As,required/As,provided, as apsix mentioned (this may not be recommended in some cases, e.g., in seismic design). If the tie is in an angle with the rebars, #8 in two directionis will be involved, As,required is even smaller.

Another thing to check is the lateral capacity of the pile as a bottom safe guard.

 

[dylansdad]

Thanks for all of the responses. The column is a steel column sitting directly in the middle of the cap. We have decided to add additional concrete at the sides and above to "cap" the pile cap. We will drill and epoxy additional bars at the sides. Thanks again for an interesting discussion.

 

[DRC1]

I would like to support Qshake on this one.
One an observational note it has only been recently I have seen hook bars in pile caps. They are more difficult to install and as Qshake pointed out do little to add capacity.
I would be careful in capping the pile cap. Be certian you can transfer the shear and tension, and that the anchors are properly installed. If the cap is suseptible to freeze thaw, besure the joint will exclude water.
My concern here would be that you would take an acceptable foundation and through the course of repair, create a problem.

 

[swivel63]

geez, i guess it really does show that if you give 20 engineers the same problem, you'll get 20 different answers.

 

[miecz]

WillisV-

I see that CRSI does not include the "nodal zone" concept. CRSI (I'm looking at the 1992 Handbook) makes some vague statements about the cross bars and compressive reactions contributing to confinement, but then doesn't modify the development length to account for these effects.

I'm coming late to the strut and tie table, and it seems that the approach is not precisely agreed upon. My point is that strut and tie begins with a fictional assumption (isolated tiny struts) that leads to a requirement that doesn't feel right (ties must be developed beyond the pile). The approach is surely conservative, but in this case, it seems too conservative.

If one includes the nodal zone concept and widens the strut width, then the development requirement seems more realistic.

 

[WillisV]

jmiec - I agree that the strut and tie design procedure is a bit in flux and is open to some interpretation and judgement. I also agree that it is a more refined procedure than that used by CRSI. My point was simply to note that CRSI had been using their own simplified tied-arch model for years for these specific pile caps that required development at the pile.

 

[J1D]

Check ACI318R-05 Appendix A, the development of the tie rebars is more the the distance from center of the pile to edge of pile cap. The anchorage seems Ok therefore.