one-way PT on steel beams?

[randomizer]

Hi fellow Structural Engineers,

I've had an architect propose that we have steel beams support our 34' one-way PT slab. It's got me a little concerned. We have had an old-school SE consulatant claim that this is fine with an L/600 non-composite design criteria.... and he proposes add studs at 12" anyway. Which seems like a bit of self-deception: that there should be a real design composite criteria if you are going to put in studs.

I'm wondering if we'll be having conflicts, shrinkage, cracking, vibration, long-term creep etc, etc?

Is there any real design criteria for this, rather than a (unverified) "rule of thumb?" I have trouble believing off-the-hip "rules of thumb" will stand up in a court room. Not unless someone really verifies that it is the standard of care in the local engineering community.

Thanks for your help!

Mike in Seattle

 

[civilperson]

What is the problem or concern that you are questioning? L/600 seems like high quality construction for live load deflection after completion. I would suggest shored concrete forms so plastic concrete does not deform the beam prior to gaining concrete strength and Post Tension compression.

 

[randomizer]

Hi civilperson,

Thank you for your quick reply.
Well, so I imagined the PT slab would be on flat forms, but wouldn't that make the situation worse by having both a live load transfer and a dead load transfer once the forms are pulled?

As for L/600, aside from a M/S < Fcr.stress -> 6.7*root_f'c, what is the tolerance of concrete for deflection?

Thank you!

Mike