Residential driveway bridge
Residential driveway bridge
(OP)
I am designing a residence to fit a very steep hillside lot. The garage requires an elevated floor, and the driveway is a bridge from the street to the garage. Bridges are outside my design experience so I will appreciate comments/criticism of this approach. I cannot find requirements in any code. The driveway dimensions are 25' wide x 36' long from street to garage. I propose a load of a medium sized truck GWV 12,500 lbs. in parallel with a SUV (Hummer) GWV 10,000 lbs. I have arrived at a composite bridge deck of 5" concrete depth over 2"x6" 18 gage corrugated steel, with wire screen and no.4 rebar for crack prevention. Corrugations will run the width direction, all supported by timber substructure. Does all that sound reasonable? Thanks for any response.






RE: Residential driveway bridge
I would recommend designing for at least the IBC live load (category 32: sidewalks, vehicular driveways and yards, subject to trucking) of 250 psf or 8,000 lb point load. Depending on the project, I might bump up the point load to 50,000 lb if dump trucks or fire trucks are a concern.
RE: Residential driveway bridge
Mike Halloran
Pembroke Pines, FL, USA
RE: Residential driveway bridge
There are more design problems to be solved than the reinforcement area and slab thickness. Handrails will be one of them.
Good Luck
RE: Residential driveway bridge
RE: Residential driveway bridge
As always - when out of your area of expertise -- you might want to hire a pro....
RE: Residential driveway bridge
RE: Residential driveway bridge
My first thought would be to use hollow core precast slabs such as Flexicore to span from the street to the garage. They are fairly light and require no forming. Many precasters make hollow core deck beams for bridges that will carry much heavier loads if required. Is that an option?
RE: Residential driveway bridge
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Please note that I am NOT suggesting that you construct the driveway from wood - it is just that the loads are applied the same way, regardless of material, and this (free) document will give you some insight without having to purchase the AASHTO specs.
Recently I was involved in the criteria development & preliminary design for a privately owned bridge. We decided that H 20 highway loading would be adequate for fire trucks & other "unexpected" uses.
Also pay just as much attention to the substructure - (treated) wood will certainly do the job, but depending on the soils you may need driven piling - get a geotech engineer involved.
www.SlideRuleEra.net
RE: Residential driveway bridge
I also express my reservation about using the pans as permanent support, if that's what you were doing. One thought would be to use heavier corrugated metal (like 3 or 5 gage) for the deck. Decking of this kind is used a lot by local governments and private owners on low volume applications, and is usually filled with bituminous instead of concrete.
In any case, I would strongly recommend that the bridge weight limit be posted, even if the insurance company doesn't require it, although I generally find that they do.
RE: Residential driveway bridge
RE: Residential driveway bridge
RE: Residential driveway bridge
In our area, emergency vehical access is the design requirement for private bridges. I'm not real conversent in bridge design but I would expect that to be something like H20 loading.
Also, in my limited experience, the most cost efective residential bridge construction has been two steel beams with heavy timber cross decking. Periodic timbers (say 6 feet oc) can be run long and would provide anchorage for diagonal kickers for lateral support of guradrails.