huangyhg

horizontal cracks in tilt up panels
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?
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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
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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.
lifting cracks probably.
mike mccann
mmc engineering
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.
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.
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
i agree with mike....check the water added. restraint condition could contribute, but like water addition issue.
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
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.
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

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