Beam Design Question
Beam Design Question
(OP)
I am trying to figure out a beam size. The beam will be 7.75 feet long and supported on both ends by a wood column. Which method below is the correct way to size the beam?
Method 1
W= Roof weight (snow+dead=65 psf) + Floor weight (40LL+ 10 DL)
W = 65 psf x 7.75' + 50 psf x 7.75'
W = 891.25 lb/ft.
Method 2
Trusses spaced 24" o.c. and the span is 24'.
Each truss is supporting 65 psf x 2' x 24' = 3120 lbs.
Truss is supported on both ends so total load on one side is 1560 lbs.
Floor joists are 16" o.c. and span 12'.
Each floor joist is supporting 50 psf x (16/12)'x 12' = 800 lbs.
Floor joists are supported on both ends by a beam so the total load one side is 400 lbs.
So the beam is supporting 1560 lbs every 2' + 400 lbs every 1.33' = 1560/2 + 400/1.33 = 1088 lb/ft.
Which is the correct method to use? If method 2 is correct am I doing it right?
Thanks.
Method 1
W= Roof weight (snow+dead=65 psf) + Floor weight (40LL+ 10 DL)
W = 65 psf x 7.75' + 50 psf x 7.75'
W = 891.25 lb/ft.
Method 2
Trusses spaced 24" o.c. and the span is 24'.
Each truss is supporting 65 psf x 2' x 24' = 3120 lbs.
Truss is supported on both ends so total load on one side is 1560 lbs.
Floor joists are 16" o.c. and span 12'.
Each floor joist is supporting 50 psf x (16/12)'x 12' = 800 lbs.
Floor joists are supported on both ends by a beam so the total load one side is 400 lbs.
So the beam is supporting 1560 lbs every 2' + 400 lbs every 1.33' = 1560/2 + 400/1.33 = 1088 lb/ft.
Which is the correct method to use? If method 2 is correct am I doing it right?
Thanks.






RE: Beam Design Question
W= Roof weight (snow+dead=65 psf) + Floor weight (40LL+ 10 DL)
W = 65 psf x 12' + 50 psf x 6'
W = 1080 lb/ft.
So I guess either way works and method 2 is really just an in depth version of method 1.
RE: Beam Design Question
Sometimes - point loads give a slightly better answer - but not really worth the effort if everything is 2' oc or less.
RE: Beam Design Question
Generally because every assumption made in the analysis and design tends to lead towards the conservative side I feel comfortable with analyzing a beam like the one described subject to a uniformly distributed load.
Regards
RE: Beam Design Question