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I-Beam Size Question
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Posted by: Kelley Marriott

06/20/2005, 10:52:28

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I would like to span my garage of 32 ft. and have a floor load of 125 pounds. What size I-Beam would I need?

Thanks Kelley







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Re: I-Beam Size Question
Re: I-Beam Size -- Kelley Marriott Post Reply Top of thread Forum
Posted by: Kelley Marriott

06/20/2005, 12:13:40

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I will be hanging TGI floor joists off this I-beam and off a ledger on the other side, the joists will be every 16 inches. Will the 16x31 still be nessasary or would a 15x35 work?

Thanks Kelley







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Re: I-Beam Size
Re: I-Beam Size -- Kelley Marriott Post Reply Top of thread Forum
Posted by: swearingen

06/20/2005, 11:30:59

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You need to have this checked by a competent structural engineer in your area, but for pricing purposes you could use the following:

Assumptions: 5' spacing between beams, 40 lb/ft beam weight, simple supports at the ends, "blocking" between beams for lateral support at 5' max intervals.

Load: 40 + 125 * 5 = 665 lb/ft
Moment: .665 * 32^2 / 8 = 85.1 ft-k.
From AISC 9th edition: 85 ft-k @ 5' unbraced length -> W16x31

Assumed member @ 40 lb/ft, actual = 31 lb/ft, OK.

Deflection: should be less than around L/240 or so:
32' x 12 / 240 = 1.6"

Actual Deflection: d = 5 * .665 * (32 * 12)^4/(384 * 29000 * 375 * 12) = 1.44" < 1.6" OK

A W16x31 is a pretty hefty member, but looks like it will do the job. Naturally, if any of the assumptions I made change, this could be significantly different. PLEASE be sure to get your particular situation checked over by a structural guy. You don't want construction problems, let alone this thing falling on your cars.







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