penetrations through post tensioned roof deck

huangyhg

penetrations through post tensioned roof deck
gentlemen:
i am involved in a remodeling project  where duct penetrations are required through a post tensioned roof deck.  would anyone care to give some generalized recommendations or guidelines to safe panel penetrations?
at this point i am questioning if penetrations that obviously do not cut the tendons, leave 50% width of the concrete panel and avoid cutting adjacent panels might be acceptable.
in this particular case   the maximum span is 16'.  the roof loading is 40#/sf snow load.
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taking out sections of concrete will alter the compressive stress, and maybe some creep stress, in the section, altering not only its stiffness, but also the ultimate strength at the point of concrete removal.  just need to check that appropriately at the sections involved.
the big fear for me would be making sure the cutting and removal don't nick the tendons and cause a "sproing!".
you need to assess each opening, but if you can locate the tendons accurately, probably will work.  if the tendons are bonded, may even be able to cut one based on your analysis.  and no "sproing" with bonded tendons.
you should consult a structural engineer for this portion of the project.  you may have to deal with other issues such as the piping geometrical effects on roof snow loading, new thermal gradients and vapour barriers.
hth
vod
what is the size of your holes?
stanlsimon,
consult a structural engineer, this is potentially very dangerous if done wrong.