Truck loading on an elevated slab

If the IBC applies, then 250 psf is probably the appropriate minimum. You probably want to design for big truck loads anyway because of fire trucks.

Maybe an H15 AASHTO truck loading?

Look here:
It also depends on if you can restrict truck sizes (using overhead height limiter bumpers). If you can't, and a large semi-truck can drive up, perhaps the full HS20-44 loading.

You need to design for the specific wheel loads including overlapping stresses. Refer to the AASHTO spec for the appropriate wheel loads. Don't forget to consider the possibility of two vehicles passing if you have two way traffic.

I designed a project a number of years ago for an HS20-44 loading and a few years later I wassurprised to see a fully loaded concrete truck on it!

We may be forced into the fire truck loading - the architect met with the fire marshall today . . .

as for the height restriction bumpers, we would do that, but the owner evidently wants delivery trucks to have access to that part of the structure, which are just as tall as any large truck that we don't want to block. So we will either design for trucks or we won't and put up a restriction bumper.

I realize that we need to check for the point load conditions for either an H20 or H15 truck, but to get into the initial ballpark, it would be easier to put a straight psf onto the slab. Where does that 250 psf for highway loading come from? Everybody seems to know/use that number, but I haven't ever seen it referenced anywhere really specific.

It is also interesting to note that the 200 or 250 psf is often used for a highway surchage on a retaining wall.

DEL2000,

I believe the 250 psf was used quite extensively over the years for sidewalk designs in urban areas where the downtown building's basements extended out to the street curbs and the sidewalks were actually concrete suspended slabs.

The fear was that in a fire, the firetrucks would drive up on the curbs, or delilvery trucks might do the same and the 250 psf was supposed to be representative of those two occurrances.

Now I'm not sure that 250 would be always equivalent to an HS20-44 truck wheel load. But it's probably not too far off.

Check out thread #507-27824. For a fire truck I would start at a uniform 350psf and then check out the actual axle loads imposed on the slab. Good Luck.

thread507-27824

The loading for highway bridges is 550 pounds per linear foot of lane, (or concentrated axle load of 18 kips). The width divided by eight feet is the number of lanes.

Here's my guess as to where the 250 psf comes from. A standard HS20 truck load has two 32 kip axles and an 8 kip axle. These three axles are a minimum of 26 feet apart. Assuming a two foot overhang at each end and a ten foot truck width, the load area is 10x30=300 sq. ft. 72000/300=240psf.

Hard to say if this is safe for preliminary design as it assumes your entire deck is covered with fully loaded trucks, but has no impact factor. In the end you'll need someone familiar with AASHTO to design the parking area.

See attached link for City of Denver amendments to IBC 2003 pertaining to fire truck loading - Section 1607.14 includes info on fire truck outrigger loading.

This is a very interesting thread. That is some very useful information mrengineer. I have a similar situation I have been dealing with for quite a while now and ended up calling Emergency One. This is the information they gave me.

Front axle 21,000#
Rear tandem axle 48,000# (24,000# per axle)
Total vehicle weight 69,000#

They stated that their rear tandem axles were about to go up to 52,000# which would put the total weight of the truck at 73,000#.

When I spoke to them about an outrigger load they said the NFPA requires them to design their outriggers for 100psi on a 24” x 24” pad. That equates to a 57,600# point load! (ouch). They would never tell me what load was actually placed on their outriggers just what they were required to design for.

It’s interesting to see that Denver has a requirement of 57,200# requirement for 2 adjacent outriggers (that would put a F.O.S. of 2 on the design of their pads).

Hope this helps.