Monday, October 17, 2011

re: cantilever balcony

I don't know a lot about PT slabs, but maybe Harold knows about this
phenomenon. I was speaking with a contractor this weekend, and though
this project was a while ago, they had some major issues with upwards
curling of cantilevered balcony slabs on a project in S Florida. They
had issues with the water draining towards and into the units because
when the slab was tensioned the balconies curled upwards. Not to
mention the corrosion problems this may cause if you are near the
coast at that joint. I imagine this is an understood issue now and
they maybe place the slabs with a slope so they level out when the
cables are tensioned?

Given the location and the construction type, this sounds like
high-end construction. Perhaps the best method of protection of the
slab and the joint will come from your architect. Many high end
balconies get tiled, and you could provide a step down of an inch or
two from the main living area, and then provide a waterproof membrane
over the slab, then a sloped thick-bed mortar tile system over the
top. There are balcony specific waterproof membrane systems on the
market that have very specific details and if followed correctly they
offer guarantees. Then maybe some type of counter-flashing to shed the
water from the wall away from the balcony slab to wall joint. Also, in
high end condos in Florida, they now commonly install sliding glass
doors with very deep tracks, like two inches or more, to prevent water
infiltration during storm events. Not exactly a big issue in Malibu.

Harold- say you have a typical flat slab with cantilevered balconies,
I see these all of the time in Florida on the coast. The top steel
will keep the cracks relatively tight, and then you can have them
epoxy injected prior to placing floor finishes. After that, would you
anticipate much movement other than very slight from long-term creep
of the steel? (Which is why you recommended PT, along with the fact
the strands are encased?)

Agree with Harold, do not depend on critical items to be properly
maintained. Especially near the coast. It is a very unforgiving
environment for steel and steel reinforced structures. There are
construction companies in Florida where all they do is rehab concrete
buildings on the coast.

Andrew Kester, PE

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