Timber T&G Floor in Garage

[KMCovert]

I need some help designing a timber-framed floor for a car storage barn for a high-end residence. Cars will not be coming into the upper timber-framed level of the garage if they are wet (they'll go in to lower level that has a slab on grade floor, to get washed down and dried. owner wants a true barn-like look so I am thinking of using a 3x6 T&G wood deck as the upper level floor, supported by a timber frame structure. Owner would like to see the T&G floor from above and below.

My questions are:

1) Since this is a detached barn / garage do I need to provide a fire rating? Do I need to follow AITC 108?

2) Must I have a wearing surface over the 3x T&G floor, even if this is a barn? The owner says he won't mind seeing daylight through any gaps that might form between adjacent planks.

3) I know that 50 psf live load is allowed for a garage but since this is wood framed I am concerned about creep deflection. I am thinking of using 100 psf. Am I being overly conservative?

4) How do I check the 3x6 T&G for the 2000# wheel load over 20 sq. inches? The week link would seem to be the tongues breaking off.

Thanks

 

[JKW05]

It sounds like this project may fall under the International Building Code as a Group U occupancy (Section 312). The type of construction/fire ratings can be determined from Tables 503, 601, and 602 (using the 2006 IBC).

Section 406 (Motor-Vehicle-Related Occupancies) also has some code items that you may want to look into. For example, Section 406.2.6 says “Parking surfaces shall be of concrete or similar noncombustible and nonabsorbent materials.”

I can’t remember where I saw it, but I thought there was a way of “guesstimating” creep in wood members. If you can find that, I would suggest sticking with the 50 psf and keeping the long-term deflections to acceptable limits.

 

[JKW05]

....also, check 406.1.1 for area limitations for Group U; You may have to go to an S-2 occupancy if you exceed the 1,000 or 3,000 SF limits.

 

[jike]

I would be careful using only 50 psf LL, unless the headroom would restrict use by larger vehicles.

AASHTO would help you with load distribution.

 

[civilperson]

Use Tongue and Groove as independent beam 6" wide and 3" deep for the 2000 pound load. Thus a support every 40" or so is required for the concentrated load on the decking, (assuming a high grade timber in a dry condition).

 

[Taro]

What building code are you using? The current IBC has changed parking garage loading substantially:
1. Decreased the uniform live load from 50 psf to 40 psf
2. Increased the concentrated load from 2000 lb to 3000 lb
3. Eliminated live load reductions except for columns supporting more than one floor.

These changes are based on an ASCE parking garage load report by Wen and Yeo.

 

[msquared48]

Questions:

What is the purlin spacing?

The owner is eventually going to see oil drips on the T& G above, even with oil drip pans, and may want to replace some strips eventually. Some oil may seep through the joints and be visible from below. This oil is a fire hazard.

I think that I would use Glulam purlins with 1.125" T& G plywood over, and 3" LW concrete over that. For the look, could install sleepers above over the slab and use 2" T&G above. Also could nail additional 2" T&G to the botom of the purlin. If he wants to see the purlins from below, then every other or third purlin could be deeper than the rest so he could read the bottom.

Mike McCann
McCann Engineering

 

[KMCovert]

Thank you all for your replies. The Architect is currently reviewing the fire rating requirements. We did a similar structure for the owner's brother but for that one we had a steel beam and concrete elevated floor (which I agree is a much better system for this application).

Thanks again.

 

[COEngineeer]

How do you go from the lower to upper garage? you have enough room for a ramp?

Never, but never question engineer's judgement