(2) 2x12 Beam

[NewOrleansPE]

I'm checking a case where someone knocked down an interior wall and spanned 20' in his one story home with a (2) 2x12 beam. The only loads are the ceiling joists that are connected to the (2) 2x12 on each side with hangers, they're not resting on the beam. There are no equipment in the attic. He also doubled up a 2x4 under each support.

The (2) 2x12 is on the interior of the home with one side resting on the exterior wall and the other side resting on an interior wall.

Question: Is it safe to assume only a dead load from the ceiling joists of 10 psf in this case to check deflection and stress? I don't see any other place where loads are coming from.

Sincerely...

 

[swsengineer]

The code requires you to also consider

Residentail
10 psf live load if uninhabitable attic without storage
20 psf live load if uninhabitable attic with storage

habitable attics would be more loading

The 10 psf DL from ceiling only sounds reasonable you just need to add the appropriate live load too.

 

[MiketheEngineer]

How are the roof rafters supported?? Trusses or hand framed?? If hand framed - they usually use a ridge beam of sorts with a kingpost kicking down to the center (your 2-2x12's)every 4' or so.

This might add quite a bit of load. If this wasn't done - look at the ridge of the roof - I'll bet its sagging in the middle.

Also - how old is the building??

 

[NewOrleansPE]

The beam is running parallel with the rafters. Rafters are hand framed with a cetner ridge beam. House is about 20 yrs old. I looked in the attic and nothing is attached to the (2) 2x12 beam other then the joists hangers.

Originaly, there was a (2)2x12 beam spanning 10'. the homeowner took out another wall to make the span now 20'. He replaced the 10' (2)2x12 beam with a new (2)2x12 beam spanning 20'. However, homeowner told me that he removed a 2x4 that was attached to the 10' span beam and to a 2x4 that was connected to 2 rafters to make room (crawl space) in the attic. But didn't replace the 2x4 bc he didn't think it was doing anything.

thanks

 

[MiketheEngineer]

It seems like you have it figured out. Do the math. I would suspect that deflection and creep will be a problem on a 20' span. Don't know the tributary area, lumber grade etc....

Check that the posts (columns) have squash blocks carrying the load to below. You could also be overloading a basement I-beam or wood beam.

Of course my favorite question to the home owner is - Why ask me now that you have already done it??

Easier to ask forgiveness than ask for permission??

 

[NewOrleansPE]

Squash Blocks ? - To help distribute the load of the beam onto the top of the double top plate and on the(2)2x4 colume below? Is that for resisting rotation of the beam as well? What is it constructed of?

Also, generally, without knowing the lumber grade and material properties of the wood on specific jobs, can you assume a conservative value for allowable yeild stress? - I always like to be on the conservative side anyway.

thanks for ya'lls help,

 

[swsengineer]

Are they are Southern Pine 2x12's? I'd just use the values for a No.2 S.Y.P. out of the NDS

 

[MiketheEngineer]

You should be able to read the grade right off the lumber. If its not there - only God knows what he used.

Squash blocks go between the floor plywood to the beam or column below. Too often, an inexperienced builder will set the first floor column right on the existing floor. If that happens in the middle of two floor joists - only the plywood ends up supporting the column - NOT good.

 

[FSS]

20psf LL and 10psf DL souns like the appropriate loads. Unfortunately a 20' length of 2-2x12's (#2 SYP) is only good for about 100 plf max. Your beam is basically not good for any reasonable load and needs to be strengthened or replaced.

 

[NewOrleansPE]

Thank you for all your replies!