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RE: Hollow Core Precast Plank Repair?

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-----Original Message-----
From: Meyer, Jonathan


Does anyone have any experience repairing deteriorated hollow core precast
planks? I have a client who processes apples and has been doing so in a
building built sometime in the 60's. The building is a steel frame with
columns and beams on about 20 foot bays (of course, there  are no drawings).
There are two floors. The roof and the second floor are (8" thick for the
floor and 6" for the roof) hollow core precast planks. The second floor has
a 6" concrete topping with an epoxy coating. The topping has numerous cracks
in it which allow wash down water to penetrate the hollow cores. Over the
years the water has found it's way to the rebar in the hollow core precast
planks - it has rusted and spalled out the bottom of many of the planks.
Some have deteriorated to the point that the whole bottom portion of the
plank has fallen. My client wants to fix the situation. We have stopped the
water infiltration by filling the floor cracks with the appropriate joint
filler, but I have not been able to find any information concerning a viable
way to repair these planks. I have recommended repair or replacement, but it
has been estimated that to replace them will take about 1.5 million.
Obviously, if we can devise a repair that is cheaper and will last, they
would prefer to do so.

Any information that is available on repair of hollow core concrete planks
would be greatly appreciated. Thanks.


Jonathan:

I have undertaken repairs to hollow core planks in a parking garage ramp -
we also installed rods which we tensioned, then grouted the cores solid. But
we had relatively easy access, and not too many to do. In another project we
replaced a single damaged double tee unit with a couple of steel beams and a
4" topping.

One problem is the weight of the repaired planks if you grout the cores. I
would first check out the capacity of the steel frame - this option may be
ruled out at that point.

If the steel frame can support the planks and a 6" topping it could probably
support an 8" RC slab - so it may be just as easy to break out planks and
place a new slab at the higher elevation. This work could be undertaken in
sections because the slab would be a one-way span.

The steel beams and topping was also a neat solution - the beams were
spanning 60', so we installed the formwork so that it was supported only by
the beams, able to deflect freely under the dead weight of the concrete so
that the finished profile exactly matched that of the double tees. With a
14" total depth of construction (I'm assuming the planks sit on top of the
steel frame) you could use 10" beams and a 4" topping. Indeed this is
probably a better solution than the 8" slab - no shoring would be required.

Peter James


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