Rebar Detailing Question 3

[RedN]

Hello,

I have recently designed a pier/footing to support a cantilevered light pole. There is a small moment carried through the anchor bolts (Mf <100 kN*m). The subcontracted rebar supplier did not follow my design schedule and details regarding the hook development across the footing-pier construction joint, similar to the detail attached (ref: quick google search).

I circled the longitudinal bar and pointed to the vertical dowel, both in red. Should that dowel tuck underneath the bottom-upper layer (circled)? That seems like the most appropriate construction detail but the rebar detailer stated it to be irrelevant. Rather they seated the dowels on top of the bottom mat entirely. Ultimately, I don't believe there will be any repercussions either way as the loads are quite small, I was just satisfying my curiosity regarding industry/construction standards. Thoughts?

 

[JAE]

The dowel simply needs to develop its hook below the construction joint (top of footing) by the required hook development length.
Whether it goes below, or above, the bottom footing mat doesn't really matter.
It is a "feel good" to have it below, but technically you just need the development length.



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[BridgeSmith]

JAE is correct; the development (embedment) of the hook into the footing is the important part. Actually, there is a substantial increase in the required development length if you have less than 2.5" of cover below the hook, because the end of the hook can break out of the concrete, straighten, and pull through the concrete, so having it on top of the bottom mat of steel may actually be better.

Anyway, the detail as shown, with the dowels on top of the bottom mat, is typical detailing for bridges and the retaining walls we do here at the DOT.

Added note: If you want to pay more for your rebar placement and have the rod busters swearing at you all day long, go right ahead and make them put the dowels underneath. they'll either have to tie them and both bottom layers before placing the bottom mat as one piece, or they'll have to thread them through the bottom mat and hold them up while tying them. Neither is something they relish doing.

 

[dik]

It's always nice to have a horizontal bar in the bend... but, not essential.

Dik

 

[BridgeSmith]

Dik, if the full capacity of the bar is developed without a bar inside the hook, there's no reason make the rebar placement any more difficult in order to have it there. If the depth from the critical section (top of the footing) to the hook was inadequate or close to the limiting value, it may be worth considering having the crossing bar on top. However, by doing so it leaves the end of the hook without a bar below it to keep it from breaking out the bottom of the footing, if the actual cover ends up being inadequate. I've seen that happen - a little rain, a little mud flows in, and oops, only an inch of bottom cover. Then, if the bar hits full tension and the hook breaks out, the bar straightens, and pulls out the top (thus the substantial reduction for hooks with less than 2.5" cover). Of course, none of that will happen in this case, but as a matter typical practice, if the hook embedment is adequate per design calcs, I think having the hook inside is better.

 

[dik]

HR10: it's not that 'more difficult' and the rebar in the hook doesn't hurt...

Dik

 

[RedN]

Interesting. Thank you all for your replies and opinions. I come from a structural steel background and have only a few substructures under my belt as a structural designer (not sure why that says civil/environmental). I had not considered the potential for a hook to straighten and agree that the principle concept is to simply develop the bar into the footing.

 

[BridgeSmith]

"it's not that 'more difficult'..."

For a wall, perhaps not. For a round column where the hooks on the #10 dowels are all pointing out from the center of the column and the bottom mat of rebar is #8s at 6" in both directions, not so easy to put them underneath.

"...rebar in the hook doesn't hurt..."

If the embedment is adequate, it doesn't help either.

 

[dik]

HR10... two different critters...

Dik

 

[BridgeSmith]

Dik...Agreed. The OP seemed to be posed as a generalized query about placing hooked dowel bars, so I tried to generalize my answer.

 

[dik]

OP: My SDF detail for your info/use.

Dik

 

[RedN]

Dik,

Thanks for the detail. The example shown was just a generalized random google search. My actual detail was just an isolated footing.

HRod : Thank you for your information and effort to write it out. Coincidentally, my pier is round. I just assumed they would tuck the bars they could and merely keep the others in plane with the BUL mat; regardless, I have taken the opinions here and of another trusted source and accepted the contractor's detail as good enough.