horizontal cracks in tilt up panels
horizontal cracks in tilt up panels
(OP)
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?






RE: horizontal cracks in tilt up panels
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,
![[pipe] pipe](https://www.tipmaster.com/images/pipe.gif)
Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
RE: horizontal cracks in tilt up panels
RE: horizontal cracks in tilt up panels
Mike McCann
MMC Engineering
RE: horizontal cracks in tilt up panels
RE: horizontal cracks in tilt up panels
RE: horizontal cracks in tilt up panels
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
RE: horizontal cracks in tilt up panels
RE: horizontal cracks in tilt up panels
Have you checked the cover to the rebar? How long are the panels? What are the properties of the mix used?
Dik
RE: horizontal cracks in tilt up panels
RE: horizontal cracks in tilt up panels
Mike McCann
MMC Engineering
RE: horizontal cracks in tilt up panels
Mike McCann
MMC Engineering
RE: horizontal cracks in tilt up panels
How did they lift the thing - through the architectural face?
RE: horizontal cracks in tilt up panels
RE: horizontal cracks in tilt up panels
Dik
RE: horizontal cracks in tilt up panels
Mike McCann
MMC Engineering
RE: horizontal cracks in tilt up panels
i.e. the structural face would have done most of its shrinkage when the architectural face shrinkage was at its maximum.
Just a thought.
RE: horizontal cracks in tilt up panels
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.
RE: horizontal cracks in tilt up panels
RE: horizontal cracks in tilt up panels
RE: horizontal cracks in tilt up panels
RE: horizontal cracks in tilt up panels
1. The edge form is assembled and the Architectural forms placed in the casting bed. Any rebar in the architectural condrete is placed.
2. The pins are placed, form oiled and the Architectural concrete placed. It is allowed to cure for 28 days, constantly being kept wet.
3. The rigid insulation is placed and the reinforcing placed for the structural section of the panel. The edge form is oiled.
4. The concrete for the structural section is placed and allowed to cure for 28 days, constantly being kept wet.
5. The panels are picked and either placed or stored flat until they can b e placed.
Mike McCann
MMC Engineering
RE: horizontal cracks in tilt up panels
In an earlier post, you stated the structural panel was cast first but your last post stated the arch panel was cast first.
Can you clarify which sequence is correct?
RE: horizontal cracks in tilt up panels
1. The Structural panel is more rigid than the Architerctural section, being thicker and probably more heavily reinforced.
2. The pins are embedded further in the structural panel than the Architectural panel, generating more moment in the structural panel.
3. Any bending from lifting in the structural panel will be amplified to the Architectural panel through the pins.
4. The cracks were discovered via sandblasting after the panels were erected.
5. Any shrinkage cracks in the Architectural panels could have been silted in during the pour of the structural panel to be washed out later by the sandblasting.
Thoughts?
Mike McCann
MMC Engineering
RE: horizontal cracks in tilt up panels
The reinforcement, lift & brace hardware, embeds, etc. for the inner structural wythe can be placed, and concrete poured, immediately... supposedly. That is generally not the case. Normally the outer wythe is given at least 2 or 3 days to cure before proceeding with the Structural wythe.
If anybody would like more info, see thermomass.com.
It is my opinion that the cracks were caused by restraint between the architectural wythe and the casting bed, normally the slab-on-grade. Depending on when the slab was poured... differential shrinkage between the two... inadequately applied bondbreaker, etc. It gets worse the bigger the panel is. Also, tilt-up cast on a slab-on-grade may cross a control joint in the slab. The joints are normally taped so they don't "read" into the face of the panel, but the movement at the joint can literally pull the yet-to-harden concrete apart. I've seen it, on more than a few occasions.
RE: horizontal cracks in tilt up panels
RE: horizontal cracks in tilt up panels
Did anyone suggest fibermesh? I don't care what you do, it's gonna crack (especially a thin slab). At least the fibermesh will help eliminate large noticeable cracks.
Is the panel very tall compared to its width? That generally will cause horizontal shrinkage cracks.
RE: horizontal cracks in tilt up panels
Concrete doesn't crack because of shrinkage. It cracks because of restraint when the shrinkage occurs.
RE: horizontal cracks in tilt up panels
A slab on grade or on another slab has restraint, right?
It can crack from lots of things: restrained shrinkage, deflection, restrained thermal deflection (like a slab in the hot sun that arches then gets pushed down with a heavier slab). The point is fibermesh allows more tensile strength. Rebar or wire seems to allow less but larger cracks.
RE: horizontal cracks in tilt up panels
Yes, but you can do lots to reduce the restraint. And sure, cracking due to external loading occurs.
I am not as persuaded by fibermesh marketers as you are.
RE: horizontal cracks in tilt up panels
RE: horizontal cracks in tilt up panels
I agree. I'd still used the steel, but add fibermesh.
I guess you'll never know if you don't try it. If the 7" slab isn't cracked, does it make sense that the 3" slab is cracked due to lifting? The stiffer panel will be under more stress, correct?
RE: horizontal cracks in tilt up panels
RE: horizontal cracks in tilt up panels
I reviewed your earlier post. I think your probably right.
Are you saying fibermesh won't help mitigate the shrinkage cracking? If so, why?
RE: horizontal cracks in tilt up panels
Only when the concrete is still in a plastic state. After the concrete hardens??? ... I guess you could say that it just doesn't have the guts.