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Fri 9 Oct 2009 - 4:51 pm UTC
I am remodeling a house and would like to figure the size of steel I beam.
the house is 44x24 single level with truss roof. I would like to remove the existing wooden beam that runs the lenght(44ft) it has steel posts every 9 ft.
I would like to span two 22ft steel I beams, with one end on each of the existing poured concrete foundation walls( 8")and install new footing and concrete pillar in the center to carry the other ends of each beam.
I would like to keep each of the 22ft spans free of posts if possable.
the floor joists are 2x10, 3/4 T&G decking. over one 22ft span is an open floor plan with living room and kitchen. over the other 22ft span is two bedrooms and bath.
Im dont know what the loads are and not sure how to figure them.
please help me!!
Sat 10 Oct 2009 - 11:13 am UTC
Hello Dave, I can help you. But I need to clear something up first. As I understand the roof trusses are supported by the walls and the beams you need support only the floor loading. Let me know if I am correct and I can get you an answer.
Sat 10 Oct 2009 - 4:08 pm UTC
Okay, we should use a live load of 40 psf and a dead load of 20 psf. The formula we need is:
I = 5 x w x L^4 / 384 x E x D
I = moment of inertia
w = 60 psf x 12' = 720 #/ft
L = 22'
D = allowable deflection = 22 x 12 / 360 = 0.73"
E = 30,000,000 psi
Plugging in the numbers, we get a required I of 174 in^4
A good choice in a 10" beam would be:
In an 8" it would be:
In case you need it, the reaction at your center column is 15,840#.
Please ask for a clarification if you have any questions. Good luck with your project, Redhoss.
Sun 11 Oct 2009 - 10:07 pm UTC
Thank you Dave. It makes an old man feel good to have anyone value his opinion. As to your question on the footing. I have no idea what your soil bearing strength might be and you probably don't either. Here is a good guideline:
If you assume a strength of 1,000 psf, a spread footing would require an area of:
15,840/1,000 = 15.84 ft^2
This would mean your footing would need to be about 4 ft square. You can adjust this number down if you feel your soil strength is greater.
You could likely get another engineer to use allowed reductions and come up with a lighter beam. However, I have yet to kill anyone (that I know of) and enjoy sleeping at night. I look forward to helping you again.
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