Beam sizing


  #1  
Old 05-13-04, 03:13 AM
Tinker Steve
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Question Beam sizing

Hello,
I have been trying to find information on beam sizing for one I want to replace in my basement .
Right now I have 4 2X8 nailed together .one end sitting on the foundation sill . A post at about 10 ft , and then a 2X6 wall supporting the other end at about another 10 ft .
I would like to increase the span to about 16 ft to get the post out of the room (home theater) .
The floor joist above are 2X10 on 24 ctr with 10 Ft span either side of beam .
the subfloor is 2X6 t&g diagonal . Finish floor is 1X4 t&g layed cross to floor joists.
There is a partition wall about 3 FT off center from the beam up above for the kitchen .It is 2X4 construction 10FT tall about 9ft long running cross the floor joists.
The ceiling upstairs is partly vaulted <follows the roof lines to 10 ft then flattens out>
Roof joist are 2X8 2 ft ctr ridge board 1X8 . 3/4 cdx sheathing and 3 tab for roofing.
My question is what size engineered lumber , Glulam,paralam,or lvl would be good for this ?
What kind of footing would the inside edge of the beam require ?
And what type of top flange hangers would be good for this application ? <simpson has a gazzilion of them >
I am plannng on cutting the floor joist , to tuck the Beam up .
Thanks , Steve
 
  #2  
Old 05-13-04, 06:11 AM
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Hi Steve,

Just my $.02 worth here, but I would look at rearranging the new home theatre rather than trying to replace the beam with an engineered product. I think you only option to replace that beam & have the new one unsupported over a 20' span would be to go with a steel I-beam. IMO, this is more expense & work than it's worth and you quite possible could do some serious damage to the structure of the home.

Others here may have different opinions, but as I said, just my $.02.
 
  #3  
Old 05-14-04, 03:04 AM
Tinker Steve
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I guess one of the main reasons for doing any thing at all to the beam is because it dosen't look very sound in its present condition . The 4 2x8 nailed together look really shabby . And it looks like scrap wood supporting it on the sill plate . I want to do some thing better than what is existing , and if i can move the post all the better .
 
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Old 05-14-04, 06:55 AM
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Well I would agree that 4 sistered 2"x8"s probably does look like sh** up there on the basement ceiling. What you could do to spruce things up & not break the bank is just to wrap the beam & the post as well with drywall & then tape & finish it. This is what is done normally in new homes with finished basements. Sounds like you can attach the drywall directly to the 2"x8"s, might have to build yourself a frame around the post, I'd use 2"x2"s and deck screws for that.

For the post, there are several brands of premade columns available on the market today. They typically used to wrap old columns on porches when updating to vinyl siding, but I have used these products for wrapping & hiding unattractive support beams in basements as well. They come in 2 parts & are just filled around the column & snap together. They have top & bottom mouolding piece that go with them to dress out the top & bottom.
 
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Old 05-16-04, 11:39 AM
howdo
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No Simple Answer

To perform such an operation, you really should get actual engineering calculations done. That said, your can get a pretty good idea of beam size by calculating the bending moment and then the required section modulus.

First you need to know your load. If you asume that it's uniformly distributed, then it's a standard 40# live load plus a 20# dead load over the area of the joist. If the area is 20ft. (10ft. on either side) times the beam length, or 400ft. sq., the total load is 400x60/2, or 12,000lbs.

The moment is then Total Load x Beam Length / 8, or 12,000x20/8=30,000.

Next you need to know the actual fiber strength of the beam you'll use. A quality glulam will run Fb=3300. Knowing that number, the section modulus of the beam can be calculated by Moment x 12 / Fb, or 30,000x12/3300=109.09.

The section modulus is a function of the geometry of crosssection of the beam: Section Modulus = Width x Depth x Depth / 6. Here's where you need to play with the width in order to determine the depth. If you select a width of 8 inches, then the calc is something like 109.09 x 6 / 8 = 81.81. Then take the square root of that, or 9.04 inches. So you'd need an 8 x 9 beam. Of course that calculation is without using a safety factor. I'm not sure what's required, but using a factor of 2, multiplied times the section modulus, the calculation would be 218.18 x 6 / 8 = 163.64, square root = 12.79. So, you'd need an 8x13 beam.

Regarding the foundation, it's a function of the soil bearing capacity. The lowest class soil can handle 1000psi. Bedrock can handle 4000. You'll need to carry 6,000lbs. at each end of the beam. You can also calculate an increase in bearing capacity of 20% for each foot of depth over the first foot for up to 3 times the original capacity. In your case, just using the weakest soil, clay, if you went 3 ft. deep, the capacity would be 1000x1.4=1,400psi. The footing area required would be 6,000/1,400=4.29ft. sq. So you'd need around a 2ft. square footing, three foot deep.

I hope this helps. Just remember that this is a predicated on a uniformly distributed load and real actual calculation would have to be made for your specific situation.

Good luck,
Dave
 
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Old 05-16-04, 07:28 PM
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Regarding soil-bearing, is that PSI, or PSF?
 
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Old 05-16-04, 07:37 PM
howdo
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Sorry Steve, my mistake, it's PSF.

Dave
 
 

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