Friday, October 14, 2011

Re: cantilver conc balcony


I would keep the full length (cantilever and backspan), use small top bars at maximum 6 inch spacing, and provide a saw cut or molded control joint over the support.  You could also add some 2" by 2" WWR over the support and extend say 2 feet each way.  You could also go with adding fibers to the concrete where I would recommend, if you go this route, using one with both polypropylene and steel fibers.  For the concrete you might double check ACI 318-08 Chapter 4 Durability Requirements that may require 4500 psi concrete and w/c of 0.45 which I would recommend anyway.  Increasing the concrete cover to 2 1/2" or 3" might also be warranted however this may make the slab overly thick.

Thomas Hunt, S.E.

Date:        10/14/2011 06:02 AM
Subject:        cantilver conc balcony

I have an exterior concrete balcony with a 15' cantilever and 10' backspan.  I expect that no matter how thick I make slab I will get deflection and a crack over the support.  would it be best to detail a pour joint over the support or cut a crack control joint to control the crack?  joint could be filled with caulk / flexible joint sealer.
Also, project is located on a bluff about 1/2 mile away and 300' above the ocean (Malibu).  For slab exposed as finish, is anything recommend fro rebar protection?  I was thinking 4000 psi conc with w/c = 0.5 max, and 2" cover.  should I include something like xypex in the mix, or increase rebar cover, or am I distant enough from ocean that salt will be a minor issue?
Thanks in advance,
Paul Franceschi
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