huangyhg

rebar details for concrete column-flat slab moment frame
i am working on a concrete flat plate parking garage using post-tension tendons. the columns are 27' cc with a slab thickness of 7.5". this project is located in washington dc area.
traditionally, if we have beams and girders, we can design concrete frames to resist lateral loads. how about flat plate systems?
first of all, can we only use concrete columns and flat plate to resist lateral loads (seismic and wind)? we try not to design additional shear walls if possible. if it is possible, what kind of rebar details are required at columns and flat slab? is there any guidline we can follow?
thanks a lot for your help.
shear walls.
i have never done a flat plate job where the plate is used as part of the lateral load resisting system other than as a diaphragm. it could be done, but your 7.5" thickness would be suspect, depending on the number of floors in your structure.
you mentioned both "flat plate" and "flat slab". i would think that to resist lateral loads, you should be using a flat slab (with drop panels), which you will probably need at any rate to resist punching shear unless your columns are large. don't forget to check the edge and corner conditions.
load reversal due to lateral loading would require more continuous reinforcement in both top and bottom, especially in the bottom over the columns.
a quick google turned up a number of references including the following:
here is an even better link
we have used flat plates and concrete columns on a number of projects as lateral system. aci permits use of this in buildings with seismic design category c or lower. look at chapter 21 of aci-318 which includes typical details for this system. this system is classified as an intermediate moment resisting frame.
i have also done several flat-plate-moment frames. they were in lower seismic regions.
onetimedeal,
forgetting about the seismic effects, i hope you have checked your deflections "properly" for this slab. you would never get away with this thincness in australia or europe for these spans!!
i have not checked the latest aci on this but earlier versions did not have a section on moment resisting frames for pt slabs, only pt beam systems.
great information. thanks a lot for everyone.
onetimedeal,
i forgot,
if you were to do it, you would not be able to use the aci pt logic of no column/middle strips for pt flat slabs. the sway effects would still have to be confined to the logical column strip as they are for rc slabs and detailed with continuous top and bottom reinforcement.
i agree with hokie66 that you would be better off with drop panels (l/3 of span, not 4'square) for both moment transfer and punchiung shear/reversal effects.

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