Structural Question

[tbob]

Hi Everyone. I got a question. I have a 22'wide x 32'deep garage that is built into a hill. The top floor has an 8x7 garage door on the back wall that is accessable by a ramp. I store my mowers and lawn and garden items up there. The floor is supported by 2x10's on 24" centers spanning 11' with one side supported on concrete walls and the other side above a 8" high x 5"wide 1/4"steel I-Beam running the length of the garage with one post support in the middle. The floor is 3/4" T & G plywood. I would like to store a 1972 442 convertible up there toward the front. If I run the car up on 2 x 12's fastened to the floor, do you think if this distribute the weight enought to hold the car? I do not know the weight of the car but I think it is around 3000# due to the fact that it is a convertable. I had a Model T up there with no problems but it is considerably lighter. Any Ideas.
Thanks, Terry

 

[JCByrd24]

The structure is not designed for the weight of the car. Typical wooden floored garages are designed for 50psf live load and usually would result in 2x12s 12" OC (on a similar span as yours) for joists and 1-1/2" decking or possibly 5/4" plywood. The steel beam also sounds undersized. Thus, you're about 0 for 3...

Now, if you are talking about really storing it, no jacking, no moving a lot, etc. You could probably get away with it if you keep in mind everything is undersized and work around it:

-you could put a couple of temporary posts under the steel beam below to support it as you move the vehicle into the garage and maybe a more permanent one depending on final parking place, this would work around the under sizing of the steel.
- Keep in mind that the center post under the steel beam and the concrete walls are your strudy supports...a wheel on the center post and/or wheels very close to concrete walls are good things, thought exactly strattling the center post could be good too. What to avoid would be parking the car with it's centerline in the middle of the 11' span, putting all the weight on 1 side of the garage, This is the work around for the joists and where I would pay very close attention to deflection below, up to about 1/4-5/16" is ok over 11'.
- You definitely want to use a 2x or two stacked over the plywood floor, 3/4" ply on 24" centers is spongey just walking on it. This would alleviate your weak subfloor.

Oh, and be careful and smart...

 

[rancherbill]

I am not a structural expert by any means.

I would think that adding extra 2x10 on 12 inch centers or sistering the existing 2x10 would be things I would look at. The 12 Inch center would be by preferred plan give the 3/4" plywood. ALL of the joists need to be braced between each other.

Around here, Totem Lumber has a Contractors Desk (NOT Home Depot or the other ones). Take in your "as built plans" of the existing structure and they will get an "expert" quote on what you need.

 

[kbs2244]

I would go find a storage unit.
That sounds like too nice a car to take that risk with.

 

[Sundowner]

I'm a structural engineer. I'd say it's too close to eyeball and give it a thumbs-up/thumbs down. I'd have to sit down and break out my steel manual and NDS wood specs and work through it, and that would take me about 2-4 hours.

Really, in things like this that are *close* the failing element is usually an un-noticed detail like how the beam is supported on the concrete block ,or how the steel beam is bolted in to it's supports. the best I could offer in good concience is that it 'might' hold.
If you're really set on storing it there, then go ahead and hire a structural to have a look at it. I figure anyone decent can sort out the numbers fairly quickly and offer a plan for strengthening in about 8-10 billable hours, including a site visit. Figure $150/hour is fair, amybe a little less for a privateer doing work on the side.