i am building a bridge from my driveway to a second story garage. there are two concrete stemwalls one at the driveway and one midspan, the joists will will rest on these. the drawings show full 2×12 hangers on a ledger attached to the garage wall. my father made these drawings and has since passed on. now, two years latter i am building this bridge. i had been wondering what this conection would look like. i recently read “attaching a deck to a water table” FHB146 Q&A. i think this is what i should do, my only modification would be to add a lag bolt into the top plate, due to the extra depth of the 2×12 ledger. has anyone built a driveable bridge/deck before? if so, any thoughts?
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Unusual situation to put into my mental database.......................
What are the spans?
What will the loading be? Car size...maximum?
What will the bridge decking be?
Can you attach some drawings?
Interesting..............................................................Iron Helix
sorry for the time gap. ive been working 24/7 on my home. the total span is 18 ft. one conc. wall at ground level. one six feet down hill. then clear for 12 ft to the garage. that makes an 18x18 bridge. the door is 16ft so we can call it 16x 18. the plans show 2x12 pt joists 12oc. and doubled under tire treads. the decking is 2x12 pt flat on top. i don't know your background, but i don't know my engineer either and he has made obvious and costly mistakes in the past. the garage rim joist is 2x12 structural sellect as are the garage floor joists 12in oc. they are on top of 2x6 frameing 12ocw/ shearwall & diaphram nailing and holddowns. the parking deck is two layers of 1and1/8 t&g plywood, which will be covered with steel sheet or conc veneer. i have already flashed the front of the garage were the bridge will contact and realised that the rim joist will take all of the load, do to the 2 and1/4 inch floor sheathing. my plan would be to place three 3/8 in bolts #8 grade w/galv finishs. next to each joist hanger, with spacer washers to 1/2 from the flasheing for air . and to use the the most ridged simpson hangers for 2x12. this would mean pre nailing the hangers to the ledger and clinching the nails. this seems excessive to me but have looked at some roten driveway bridges/garage entrences lately just snooping around.
I have seen many horrible bridges designed by building engineers. If the engineer is horrible, you should move on anyway. There are many structural engineers aroud that should be able to design it right, without specifying a timber trestle.
Hold the span dimension at 18 feet. Anything 20 foot or over is officially a bridge and could require biennial inspections by state DOT forces or consultants (if they find it), and I'm sure you don't want that....that's not a mistake, it's rustic
Hanging an 18' bridge on a 2X12 ledger seems nuts to me. The whole thing on one board?
And 1X12s spanning 18' carrying a serious load also sounds like it's much, much too little.
I'd scrap the wood and look at spancrete.
Truss Designer Extraordinaire
O.K. - I juat re-read it and realized there was a wall partway in. SO the span isn't as bad as I thought.
But I still don't like hanging the weight of a car fomr a ledger......
Truss Designer Extraordinaire
Just could not shake this discussion out of my mind..............so I referenced a couple of items.
Assume the car is wheel based at 9 ft and its weight is 4800 pound. This means each wheel exerts 1200# on the 2-2x12-12' beam upon which it rides. The greatest uniform load equivilent is reached when a single wheel is at the center of each 2-2x12-12' beam. This uniform load per foot "W"=4x total load on the beam/ divided by the beam length. Therefore 1200# point load at the center of the beam x 4/12 ft= 400 lb/ft uniform load equivilent.
The Southern Pine Association lists the allowable uniform load per foot of a double 2x12 with a 12' span as 329 lb/foot. The design is not stout enough for a static load let alone a moving load. And I have not added the weight of the materials or a snow load !!!!
A triple southern pine 2x12 with 12' span has a 494 lb/ ft uniform load capacity. I would certainly upgrade at least to this size. If you add materials loads and any other loads, plus a safety factor....this triple may not be okay.
Second consideration should be given to the possibilty that the cars that may use this bridge may not "track" the same......so where to place the triple drive beam? Or how do we allow a delivery truck like UPS to show up at the garage?
Third consideration... time, weathering, insect invasion, and constant flexing due to a moving load will cause deterioration of the wood bridge strength.
Take another look at your plan...consider upgrading........or pay the piper (engineer).
IMHO.......................................Iron Helix
YO Iron -
Or should I call you Mr. Helix?
When I've designed trusses for garage floors, I was required to do the following:
1. Design the floor truss for a 50PSF live load over the whole floor.
2. Design the truss for 150% of the MAX wheel weight ANYWHERE on the floor. (Without the 50 PSF live load) Keep in mind that most cars are heavier on the front end. And the guy may have a full sized pickup.
I'm not sure if BOCA required that, or if it was the truss plate institute. Haven't done one in a while.
Truss Designer Extraordinaire