Ferroscanning of precast panels 2

[darthsoilsguy2]

Hello,

i work with testing/inspection. we use a Hilti Ferroscanner to locate rebar prior to coring (usually to resolve bad concrete breaks). an interior design architect who knows us asked us to scan some old exterior precast wall panels so they could put window and door openings in a few panels. His Structural Egr wanted to know size/spacing of bars.

the panels are 12' wide, about 40-50' tall, and about 6-7 inches thick.

i did some scanning in 2'x2' blocks inside the proposed opening locations. the 4'x4' window and 3'x7' door locations that were in the center of the panel had no vertical reinforcing steel. openings near at the edge would have 2 or 3 vertical steel lines. Horizontal steel was around 18" on center but not consistently.

i've never designed or seen precast made, but i've inspected tilt-up walls before. The amount of reinforcing in tilt-up is much much much more.

if you've read this far, then you know my questions probably by now....

1. These are prestressed.... right?
2. Probably bonded tendons???
3. i'm right to think putting a 4'x4'or 3'x7' hole through tendons can spell disaster?
4. i'm right to think that putting those holes in a prestressed panel... even with no tendon cutting still can make big problems?
5. i could be wrong and this could be just rebar and that is why my name is not DarthPrecastGuy?

Post rule: no telling me to report it to the SE cause he'll know the answer and it's his problem. i'll do it... but i want to confirm or refute my hunch (before i open my mouth).

 

[concretemasonry]

It sounds like they may be older site-cast panels that do not have the controls imposed by the PCI certifications that are almost universal today. - Length and width make movement very difficult and 4' or 8' wide plant produced panels are now much more predictable, and economical depending on the time of construction and location in the country.

I would not jump to the assumption of prestressed. You may have rebar placed sloppily.

Are there any original drawings or shop drawings?

Dick

 

[darthsoilsguy2]

the only plans are new architecturals that were drafted recently.

now that i have it in front of me.

The panels are 12' wide, 35' long, and 6" thick.

i should have said that my 2x2 scans are grouped together so they are really 4' wide x 2' long centered at the proposed opening.

i used the scanner as a stud checker on a couple of other panels and found that the middle 4' of each panel had no vertical steel consistently.

Thanks

 

[darthsoilsguy2]

Update -

I told the SE that i thought they were prestressed. He got worried and started to looking into it more and located the original fabricator. The panels are prestressed and fabricated by Tindall precast. The architect is getting direction from them and will have to change their wall penetration layout to avoid tendons. The 6" panels are 2-2-2 (2" of insulation in the middle i was not aware of).

Also,
for future searchs on this topic. The plant engineer at one of the precast manufacturers that i checked with told me that the tendon can be checked at the ends. You can go below grade and drill a hole where the vertical steel signal is coming from. If it is a bonded tendon, the stressing from the tendon is not doing much at the end of the panel. it's a good place to look and see if there is a cable or if there is rebar.

-DarthPrecastGuy (for a limited time only)

 

[hokie66]

Very good. You followed through, defined the problem, now it is well on the way to being solved.