Garage floor wheel load 1

[JStructsteel]

For the 3K wheel load on a elevated slab, what distribution width would you use? I have 4" slab on 1" form deck. Beam spacing about 5' max. I was figuring 30" to 36" distribution width. Thoughts?

I see in PCI for a double tee example they use 60 deg angle back to the web. granted i am not really a cantilever type slab, but just a one way.

 

[XR250]

For one way, I think I would use my rebar spacing or maybe 12" or I suppose you could distribute over multiple bars using lateral reinforcement.
Seems like a lot of load for a 4" slab though. Shear may be an issue.
Admittedly, I don't do too much concrete design so you should probably listen to someone else.

 

[JStructsteel]

Lol, thanks XR250. Im basing it off my experience too with Double Tees for parking garages. They seem to work all day with 4" flanges. The PCI manual example distributes back over a 8' width! Im confident if can be at least a couple feet, 3 feet could be pushing it.

Slab design seems to check out with moderate reinforcing. I will check shear.

 

[lexeng18]

60% of the beam spacing for me. Theres a reference somewhere around here for that percentage, cant find it currently though.

This usually works out to be about the same width as a 30 deg angle each way with the point load between the 2 beams.

 

[SWComposites]

what about the single jack stand load holding up one end of the vehicle? happens all the time in home garages.

 

[lexeng18]

I would still argue a 60% effective width even for a jack stand load. the 3,000lbs is supposed to account for exactly that.

 

[Celt83]

Sounds like you may have a slab on deck, SDI has provisions for determining the effective width: Link

 

[XR250]

If it is form deck, wouldn't he just use ACI?

 

[BridgeSmith]

Full scale testing of concrete bridge decks on steel beams determined that bridge decks don't fail in flexure; they fail in punching shear, at a load of about 5 times the AASHTO design wheel load (16 kips). AASHTO now has provisions for "Empirical" deck design, which has less than half of the reinforcing used in the "Traditional" deck design, based on flexure. There are some limitations for the empirical, which you may not meet with what you're doing, but apparently the arching action that distributes the load is significantly more what has traditionally been assumed.

OTOH, a word of caution when looking at the flanges of precast beams - the concrete strength is typically much higher than you'd find in a CIP slab (6 to 7 ksi is common for prestressed beams).

All that to say, shear capacity is what you need to take a close look at.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[JStructsteel]

SWComposites, Im using the code prescribed 3K load. Even a car on 1 end still means the car can be 6K.

Celt83, thanks, will take a look

BridgeSmith, this is a residential garage over a basement. No truck traffic hopefully!

 

[Tomfh]

We saw a funny one where a jack lifting a 4WD/suv punched through a waffle pod slab on ground. It was roughly 3”.

 

[JStructsteel]

Just the legs punch thru, or the whole thing?

 

[BridgeSmith]

BridgeSmith, this is a residential garage over a basement. No truck traffic hopefully!

I hope not; our deck slabs are 8" thick, and even using the empirical design, would probably be considered heavily reinforced, compared to most residential, and even commercial construction.

Anyway, it was just an illustration/analogy showing that the distribution width in an actual slab is significantly greater than what has traditionally been assumed and used in analysis. It also indicates the failure mode (punching shear) that you may want to take a close look at when determining the capacity.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Tomfh]

Just the legs punch thru, or the whole thing?

Just the jack. So quite pointy compared to a wheel.