Replacing Undersized Beam

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  #1  
Old 03-07-07, 08:15 AM
M
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Replacing Undersized Beam

Hello,
I am planning an addition on a 24'w x 32'l bungalow in MD. We are adding a second story and room-in-attic trusses. The existing 32' main beam has signs of damage and is only 4 2x8s sistered together. It sits roughly 10 ft from one exterior wall and 14 from the other and rests on two block columns.
Our architect looked at the beam and proposed replacing it with a bearing wall (probably constructed with 2x6s spaced 24" o.c). We had considered a steel beam, but given th edifficulty of getting a large piece of steel installed (we are doing most of the building ourselves - i have several years of framing experience, but 0 years of structural engineering)
He said that to support this wall, we would need to channel out the paper thin existing concrete floor and put in a footing (w/rebar) only 8 inches deep.
Of course we know that we have to build temporary walls to support the overlapping floor joists above, but I am wondering if this footing depth seems sufficient?
Any advice or recommendations on this project would be greatly appreciated.
Thanks so much!
CR
 
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Old 03-07-07, 02:35 PM
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Replacing Undersized Beam

The 8" would be adequate if you know you have good undistubed soil. Usually the soil in a basement is the junk and scrap a builder covers up with a thin slab. - You won't know what you have until you open it up since you will probably have some pipes buried with no compaction of the soil.

I would plan on 10" or 12" since you have the 2x6 spaced at 24" just to be safe. The width should be at least 16". This is still less than your exterior walls, which probably have less vertical load than the interior wall will have.

Dick
 
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Old 03-07-07, 03:00 PM
M
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thank you so much! we'll have to see what lies beneath - we have a lot of clay in the soil where we live, but who knows what got dumped down there in 1928 when the house was built.
if we decide to go with 2 x 4s for the bearing wall, can we narrow the footing (to maybe 10") so that we pour a 10" x 10" footing (over several inches of gravel)?
 

Last edited by MDAddition; 03-08-07 at 11:41 AM.
 

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