I have a 30×24 2 story house with basement that has a sagging beam that is starting to crack, and I want to replace it before it gets worse. It is in the center of the house, running the length (30ft), supported by two brick columns that are in good shape, evenly spaced (10ft on center). This beam supports the two floors above it. Right now it is a rough 4×8 with a 2x on top that the floor joists sit on top of, with the center wall of the house resting on it, also carrying the center floor joists of the upstairs. I’m figuring a load of 40lbs for the house, and snow load isn’t a problem. I don’t really want to have to narrow the openings in the basement by putting in another support, so I’d like to span the existing distance.
Steel or LVL? Open to suggestions.
Replies
So what's the total height available between the top of the columns and the bottom of the joists?
around 9½" total with the 2x on top, plus the rough cut 4x8 underneath.
A lod of 40# isn't adequate for residential loading. The 40# is only the live load - You need to figure dead loads too.
What about the roof framing? Does some of that bear on the beam? Or just ceiling framing?
Even if there's no snow load, you still have to figure SOME live load for the roof area.
The roof is trussed, and the weight should be distributed on the outer walls.As far as the dead load, I'm not sure exactly how to calculate that.
Dead load here is a figure determined by the AHJ.
I figure floors at 55 PFS total - 40# live and 15 dead. Unless you have tile or lightweight cnocrete on the floors that should be plenty.If you're carrying about 12' on both floors, that works out to 960 PLF live and 1,320 PLF total.For LVLs, that works out to either a pair of 11 7/8" or a triple 9 1/2".With a steel beam, a W8X15 or heavier would work. Since I don't know where you're at or what you local codes might say, all of the above should be verified, of course.
Boss, Remember there are two floors above this.12' PLF times 55# per floor(2) is 12 x 110 = 1320No wonder the existing is in failure. It is about a third of the size it ought.
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"12' PLF times 55# per floor(2) is 12 x 110 = 1320"
Which is why I said:
"...that works out to 960 PLF live and 1,320 PLF total."
I can see clearly now, the brain is gone.
What happened to my eyes on that tail end of the sentence????
'scuse me while I go rustle up a carrot or two
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Are you sure your roof trusses have been designed for full span, outside wall to outside wall?
"Are you sure your roof trusses have been designed for full span, outside wall to outside wall?"
I think that's a reasonable assumption. No way in hell is anyone gonna build a 24' roof truss that's center bearing.
He can do more for others who has done most with himself. [S.D. Gordon]
Is there a second floor wall that lines up directly above a first floor bearing wall that is directly over the bearing line in the basement?
What difference would that make?
I don’t jog – it makes the ice jump right out of my glass.
That may put some doubt into your assumption the trusses were designed for spanning outside wall to outside wall.
Not at all.I've been designing trusses for 20+ years, and have never seen one that small that was designed for a center bearing.
Pentiums melt in your PC, not in your hand.
OK.
It's kinda scary to say much about this based on a little bit of information over the internet. We have no idea how fast this is failing, or what other structural issues there may be with this building. Give us your location. Perhaps somebody here can recommend a local contractor to check this out in person. On this kind of thing, you have to look at the whole big picture, not just the beam.
Is there anything happening upstairs in the house as a result of this? Like cracks in the plaster, doors not closing right? Did the cracking just suddenly appear? If so, get a house mover out there pronto to stack up a bunch of cribbing and stabilize the situation.
OTOH, spontaneous catastrophic collapses are extremely rare. We had one out here about five years ago, an apartment building. It killed one guy and put two dozen families on the street.
-- J.S.