huangyhg

floor vibration--no concrete
i am designing a second floor "beer garden" as part of a restaurant project. the floor system consists of type b deck on open web joists, without concrete topping. there will be rigid insulation on top of the deck, and 2" concrete pavers on top of the insulation.
i intend to check vibration, and use the noncomposite section properties (again, no concrete) for the joists and beams. does that make sense? anyone else ever dealt with this?
daveatkins
seems to me, this is not much different than a roof with pavers. roofs can be bouncy since there is little mass and little damping. your analysis approach sounds logical but i would guess that the owner won't be happy with the potential movement.
just out of curosity, is this outside? if so, i assume there will be a membrane and drains similar to a roof.
jike,
yes, it is outside, and yes, it is essentially a roof with pavers.
i plan to beef up the beams and joists to make the vibration check out. my fear is that it will be difficult, since the conrete topping contributes so much to the stiffness of the system.
i may end up adding concrete topping, just for stiffness.
daveatkins
it has been a while since i did a vibration check, but am i correct in saying that you need to check the frequency as well as the acceleration?
the frequency may be problematic because of the lack of stiffness (not having composite concrete topping, not to mention open web joists are generally less stiff than wf).
i suspect the acceleration will also be a problem because there is little mass, so when you do the footfall check the acceleration will be higher than if you had concrete topping. the pavers should help somewhat, but not like a concrete topping.
dave, i think you are right on, the sections will be noncomposite and it will be difficult to meet the thomas murray vibration criteria.
you should alert the owner/architect of the potential problem.
the concrete pavers will only help with the effective weight (w) of the joist panel.
we have added sand bags to joists to help dampen the vibration when it has been perceived to be a problem.
dave,
i have done designs where steel beams support only timber joists with similar loading and we have beeen able to make them work. in this case you have the 2" concrete pavers to provide some weight to help keep it down.
the floor to ceiling depth will be much higher than the composite floor though.
this will be one of those cases where you design for vibration and check for strength afterwards.

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