Residential beam sizing question

[dmccarty]

ejb,

One of my job titles is Software Engineer. I have read up on structural design but I ain't no PE that is for sure. Since you get what you pay for and I'm not charging anything.... /forums/images/graemlins/grin.gif

Look up tributary loads which is the situation I think you are having to handle. A picture explains this easier than text but I'll try. I think you need to calculate the area that the load bearing wall/beam to be supports. Then you need to figure out the dead and live load in the space above the wall. I think the rule of thumb is that dead wieght of the structure i.e., the wood, nails, etc. is 7 pounds per square foot. I just use 10 for extra measure and making the math easier. The live load depends on what you want to do with that space. Live loads for living space in houses runs from 30-40 pounds per square foot assuming my memory is working and my class from years ago was right. For attic space you might be able to go with a lower pounds per square foot.

The tributary load is the area that runs the length of the wall/beam times half the distance on each side of the wall/beam to the next load bearing wall.

A picture would help but I don't have one. /forums/images/graemlins/grin.gif

Take the area supported by the beam times the live and dead loads and you have the wieght that needs to be supported and you can then figure out the beam size.

Later,
Dan

 

[RobS]

Good advice, I'll just add this since I didn't see it mentioned:

If I understand it right, the joists you mention run perpendicular to the roof ridge. If that is the case, the joists also carry a horizontal load in keeping the outer walls/roof from spreading out due to the pitch of the roof. If you let the beam/header into the joists you'll have to account for that load in the fastening (if that's even possible/allowable).

Good luck and be sure to post your solution /forums/images/graemlins/smile.gif

 

[chucko]

Ceiling load is what we are talking about right? If so it only is more like 10 psf assuming drywall was used....maybe a little more for plaster. Plaster has a much higher deflection requirement. Anyone that sales the beams can figure what you need is less than 5 mins.


for hangers look for the simpson site. I am sure they have something

 

[chucko]

ok if I understood right your beam will need to hold
122.1 PLF

 

[chucko]

1 (2 ply) 1.75 x 9.5 Versa-lam (that is all i have in my software at this time) will work.

(have the beam company duble check this before using)

 

[ejb]

Hi all again..thanks for all the responses...I did go to the lumber yard where they sell the LVL and he recommended a 2 LVL beams sandwiched together; the beams he recommended were 1 3/4 width by 9in height...he felt pretty confident that it would work fine....good enough.

So I went home and just for kicks called up Georgia pacific, (the company that makes the beams). After getting transferred around a bit I got the engireering dept who were very helpful.

He told me that I would need 3, 14inch LVL beams or 2 16 inch beams to carry the load.....

Great, so I talk to two different people, both of whom are supposed to know the answer and get two VERY different answers...

One guys say 2ply 9 inch beam, the other 3ply 14 inch beam....good help sure is hard to find.

I think I'll end up going with the 2ply 9inch beam AND put a column towards the middle, so I'll have 2 10 foot spans instead of one 20....better safe than sorry; didn't want a column, but it will be OK in my situation...you would think these guys could give me the same answer...I gave them both the exact same info.
/forums/images/graemlins/tongue.gif

 

[JJT]

I did a similar job for a friend a few years ago, only a 19' span. I used an 8x12 for the header/girt, with 3 8x8 posts and 4 knee braces, (all white pine). A post on either end and 1 in the middle. I do some timberframing on the side, it took 24 hours to plane, sand, notch and seal the beams. A friend and I showed up at noon, 2 other guys had done the demo and a temporary shore up job in the AM and left when we showed up. The beam and posts were in place by 6PM.

The 8x12 was serious overkill, but the job was a freebie for a friend and that's what I had laying around.

If it were me, I'd go with solid wood and leave it exposed.

 

[chucko]

Seems to me the guy at GP thought it had the whole roof load and not just the ceiling.
Seems the lumber yard came up with almost the exact beam I did

It is holding the cieling only right?

 

[ejb]

>>It is holding the cieling only right?

Yep...and I told him that, but I think you are right, he probably ran it the wrong way. 3x14 seems like overkill to me.