car lift over framedsteel decking

huangyhg

car lift over framed/steel decking
the owner wants a couple of 4 posts car lifts in his garage.  i think i am going to use steel decking and 4" of concrete.  i will put steel beam right underneat the lift posts.  how do you think i should attach the post?  shall i just anchor them to the elevated slab?  or shall i somehow connect the post straight to the steel beams?  comments?
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as the owner, i'd prefer to have it mounted on the concrete, so i could move it, but as the structural, i'd like to lock the location.
depending on maximum lift capacity, can the slab handle the post load if it off the beam by "x" inches"?  
it is unlikely that the loads will be much more than 2 to 3 k per post, and the right base plate might give flexibility in locating them.
if you can design for a little flexibility, i'd try do that.
otherwise, you could stub up from the beam with a wf or hss and cap it with a plate which would be at finished floor level, allowing the lift baseplates to be welded in place.
grandcasita, i think i will use hss with a plate at the finish floor.  i think i will tell them to weld all thread rod on the plate so i can bolt down the posts (so they can remove it if they have to).  do you think i should put expansion material arround the hss?
make sure you leave a little room for deadload deflection.  if you set the base plate at finished floor elevation, then place the deck....the beams will deflect and lower the base plate below the finished floor elevation.  no need for expansion joint material around the post.  it isn't put around columns going through floors, so i don't see why here.
ok.. last question.   so the capacity of this lift is 9000 lb.  so i just go ahead and divide that number to 4 (assume the owner will load it up to max capacity).  so i have this live load, plus the dead load of the lifts.  then i design the floor for 50 psf ll or 3000 point load.  do you think l/480 ll and l/240 dl deflection limit is enough?  do i need to look at vibration when they run the lift (i have never done this calc. before).  thanks for your help!
tw,
i don't see a way for this to happen, unless slab and beam do not move together.
the cap plate would generally be larger than the tube, so the plate would effectively connect the slab to the beam at that location.  which brings up the question about this apparently being non-composite, and the vertical tube becoming a shear connector...another topic for another thread.  at any rate, you probably don't want a path for spilled motor oil and antifreeze to run from under the lift to the area below, so i'd say "no" to expansion material.
as to loading, do not assume equal load on each post - pickup trucks (esp. with diesel engines) are heavier in front.  design for some variation... then factor it. on the other hand, the lift may be designed for 9k/4 on each post, so that might be your live load.
50 psf ll over the lift area plus the lift load is probably overdesign.  it is likely that you'd design the slab for the 50 (or whatever), but the structure below would be designed for the greater of either the psf ll or the vehicle weight/lift post load.  the weight of the empty lift can probably be called dead load, since it will be "permanently installed equipment."
asce 7-02:
section 4.7.2 might also apply.  
also check note 1 on table 4-1.  
note that 50 ll changed to 40 ll (in 2002) but the allowable reduction also changed.
ibc table 1604.3: l/360 ll & l/240 l+d for floors. ymmv
wow.. thanks grand.  i hardly ever look at asce.  i just look at ibc most of the time unless it refers something to asce.  i will double the load for the lift to 18k.
i wouldn't assume the load goes equally to all four posts.  that's like saying the cog of the load is in the same location as your center of supports.  i would also increase the load for dynamic impact.  contact the manufacturer of the lift and ask if they have a special deflection criterion they require or recommend.  you should consider using the maximum load of the crane and not just the maximum load rating to help ensure that an overload will fail the lift and not your structure.
i dont see why you are making it so complicated. why dont you just drill straight through the slab and through the top of the beam. chemical anchor around the beam for shear.
these types of things are much easier if they can be installed after the main   
grand,
i was stating that during concrete placement, the beams will deflect under the weight of the wet concrete.  the hss and plate will deflect with the beam since it is attached.  but the top of concrete will remain at the desired finished floor elevation, we hope.  if you set the plate height at finished floor elevation, then the finished plate elevation, after concrete placement, will be beam deflection below the finished floor elevation.  i don't know the beam spans or what the deflection is, but we had similar situations where we had 1" dead load deflections that we had to account for.
csd, thanks for the reply.  so you suggest to only increase 20% instead of 100% that asce suggested? if you want to drill trough the slab and and trough the beam, how do you make sure you are lined up?  i think the column base plate will be wider than my steel beam width.  now they even want me to wood frame the floor instead of steel decking.