Tilt Panel Reinforcing

[msquared48]

A client wants to put in a new opening in an existing solid concrete tilt-up wall that is in the order of 16 feet wide (quite long in my opinion and I will push for less).

That being said, X-ray scans show #7 verticals at an average of 17" on center with #5 horizontals. There is 3" of cover on the #7 bars.

This seems like a lot of reinforcing to me for a 22 foot high, 6" thick panel. I have never used over #5 bars for a panel of this thickness and height, going to two layers of reinforcing at short panel legs where necessary to limit the bar size. These bars appear to be placed in a single layer at the center of the panel.

Has anyone constructed panels in this manner using larger rebar? If so, was there any reason to go with larger bars in the center rather than two layers - and I would not expect to have to use two layers of bars in a solid panel. I would expect #4 or #5 @14 to 15" OC in the center of the panel.

Current As = .6/1.43 = .42 in sq./ft. => #5 @ 8" OC for smaller bars in the center. Panel seems over-reinforced to me. Lifting would not have changed the reinforcing that much... Shear? Seems to be plenty of wall though.

Am I missing something here?

Mike McCann, PE, SE (WA, HI)

 

[KootK]

All I can offer for advice is to confirm that I also find those big bars surprising. I do a bit of precast work and a conversation that I regularly have with my client goes something like this "I've got this other stuff taking up space in the yard, can I use it instead?". Maybe this is one of those.

 

[JAE]

The #7 @ 17" gets you just over 0.5% reinforcement. I wonder if they were trying to meet ACI's min. 0.5% for an "architectural column" (vs. 1% min).
Are these panels load bearing for gravity loads? I'd assume so.

 

[msquared48]

Yes, but that should not generate that level of reinforcing in my opinion.

No drawings either... Could have been designed under PCA Slender Wall Design methodology in the 90’s.

Minimum panel reinforcing for shear at .0025bt = .18 => #4 @12...

Mike McCann, PE, SE (WA, HI)

 

[Brad805]

Was the tilt panel particularly large or and odd pattern for the lifters? #7 does seem odd for a 6" panel.

 

[hokie66]

Brad asks a good question. If the opening wants to be 16' wide, just how wide is the panel? Or does it involve more than one panel?

 

[msquared48]

Hokie: I still need to make a site visit yet to see. I am concerned over that too. Will need an interior full height frame to support the wall. Right now, the panel has no openings as far as I can tell.

Mike McCann, PE, SE (WA, HI)

 

[Agent666]

Not that I've done the numbers, but wouldn't that level of reinforcement in a 6" panel possibly fail the balanced strain conditions as well for face loading?

Are you sure its not a shear wall bracing some significant loads? Either permanent or transient?

 

[PROFR]

Msquared48, This is definitely too much for a 6 in. wall. I would say the X-ray scans are not very accurate. Before you take any action, try to expose any of these rebar by chipping the concrete in a limited area.

 

[Ingenuity]

...X-ray scans show #7 verticals...

Mike: Are you certain it was X-ray and not GPR (subsurface radar) scanning?

With GPR it is seldom you can be definitive on rebar diameter.

I concur with PROFR - even if X-ray was the scanning technique used - have the contractor do some limited invasive probing to verify rebar dia BEFORE they make the panel cuts.

 

[msquared48]

Krazan, a local testing agency, did the analysis, and the report did state X-ray.

I am going to the site tomorrow...

Mike McCann, PE, SE (WA, HI)

 

[r13]

Bring a hammer with you

 

[msquared48]

Just went to the site and the panel width is 6.5" with 1/2" reveals leaving a net 6" structural panel thickness.

Also, the opening is 13'-2", and the panel is bearing, so will have to reinforce from the inside anyway.

Plenty of shearwall available, even with new openings.

I am toying with the suggestion to verify the size of the bars in the field...

The size still bugs me...



Mike McCann, PE, SE (WA, HI)