horizontal cracks in tilt up panels 2

[calculor1]

Just recently completed a tiltup project with 10 inch panels (7" + 3" architectural face). The architect called me to say the panels had developed long horizontal cracks that penetrated the full depth of the architectural face. These cracks are not a result of deflection as I have rechecked my calcs and that seems okay. Just wondering if anybody has had a similar experience with sandwich panels?

 

[Qshake]

So far you say that you have rechecked your calcs for deflection problems. However, your problem may originate at the site not the engineering desk.

If the concrete was not at strength when lifted, that's a problem. Can you determine this condition?

If the concrete is still not at strength or gaining strength as it should, this is a problem. Can you determine this condition?

If the wrong reinforcing was placed or placed incorrectly, this can be a problem....can you determine this condition?

There are likely other conditions to check for also.

Good luck

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[calculor1]

Yes I have reviewed field reports for reinforcement inspection they appear to be inorder and I reviewed all concrete reports and yes they all meet project specs. I'm thinking the cracking is more related to creep and the fact this is a sandwich type panel with the composite connectors of which I'm not a big fan.

 

[msquared48]

Lifting cracks probably.

Mike McCann
MMC Engineering

 

[hokie66]

When you say this is a "sandwich panel", does that mean the two layers were cast at different times? An explanation of how the panels were cast would help. My guess is the cracking is due to differential shrinkage of the two parts, and the structural layer restrained the architectural layer.

 

[calculor1]

The panel consist of a 7" thick structural face, 2" rigid insulation with composite pins at 12" oc and 3" thick architectural face. Structural face placed first cured, insulation and pins installed then architectural face placed and cured. I've designed miles of this type of wall and have never encountered this issue before.I can't see differential shrinkage due to the composite pins and insulation between layers. Also have a hard time believing it's due to lifting.

 

[msquared48]

If these were cast architectural face up, then lifting is probably not the issue, as the architectural face would be on the upside of the lift.

Better verify the water concrete of the mix with the concrete company. Seen a lot of water added onsite, whichis usually the case, that may have affected the shrinkage.

Mike McCann
MMC Engineering

 

[Ron]

I agree with Mike....check the water added. Restraint condition could contribute, but like water addition issue.

 

[dik]

Likely cast with architectural face down, I would think. Also, there could be some adhesion/suction in lifting the panel from the mold. This would cause cracking of the panel face.

Have you checked the cover to the rebar? How long are the panels? What are the properties of the mix used?

Dik

 

[hokie66]

Is there reinforcing in the 3" skin? By architectural face, what do you mean? Profiled face? Coloured concrete? When you say composite face, do you mean there is composite action between the two, or just that the face is a veneer tied to the backup? If it is truly composite, the pins would be very stiff.

 

[msquared48]

I don't know how it would be cast A face down when the A face was poured last. That makes no sense.

Mike McCann
MMC Engineering

 

[msquared48]

Although opposite of what was stated, it is most logical to me to pour the A section first, place the foam, then pour the structural section. If this were the case, then lifting cracks could be seen on the A face.

Mike McCann
MMC Engineering

 

[JAE]

I always thought that the architectural face was placed face down first. Then the insulation, then the structural. The lifting inserts to lift and place the panels would be in the back side structural face, right?

How did they lift the thing - through the architectural face?

 

[darthsoilsguy2]

how many panels done in the pour? how many panels cracked? if only a few... could a retempered cold joint(s) be at play? we include a concrete placement log with truck times in our testing so downtime is documented.

 

[dik]

JAE... my understanding, too...

Dik

 

[msquared48]

Architectural levitation

Mike McCann
MMC Engineering

 

[csd72]

If the structural face was cast, has subsequent plastic shrinkage and the the architectural face was cast then the structural face would act as a restraint to the architectural face shrinkage.
i.e. the structural face would have done most of its shrinkage when the architectural face shrinkage was at its maximum.
Just a thought.

 

[hokie66]

csd72,

That was my thought also, as expressed above. But the OP believes the 2" layer of insulation between the two layers of concrete makes that unlikely. I don't know much about what makes this type panel act compositely, but still think our differential shrinkage theory is a possibility.

 

[csd72]

The 2" insulation has no relevance if the ends of the panels are closed off with concrete - this is where the restraint is.

 

[calculor1]

The Arch face was cast first, the only way the arch face is attached to the structural face is via the composite pins, essentially when the panel is erected it hangs off the face of the structural panel and the ends of the panel are not closed off with concrete therefore there is no restraint provided by the structural panel. BTW these panels were cast almost a year ago and the cracks are only noticed because they starting sand blasting the panels.