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Posted by dpb on April 24, 2008, 1:52 pm
Robert Allison wrote:
...
> When I do things like this on my own, I always overengineer, because I
> cannot properly do the calculations, so I overbuild to compensate. ...
If you don't do the calculations, how do you know you're "over"-engineered?
:)
--
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Posted by Robert Allison on April 24, 2008, 2:14 pm
dpb wrote:
> Robert Allison wrote:
> ...
>
>> When I do things like this on my own, I always overengineer, because I
>> cannot properly do the calculations, so I overbuild to compensate. ...
>
>
> If you don't do the calculations, how do you know you're "over"-engineered?
>
> :)
>
> --
I can do the calculations on alot of things, but, from my
experience, anything I design gets downsized if an engineer looks
at it. I have worked with a lot of engineers, sometimes I use
them, some times I don't. I know generally what is required and
how to use span tables, but....
For instance, if I need to put a footer under a post load, my
footer will be much larger than what an engineer would design. I
do that "just to make sure".
Every time I take something that I designed to my favorite
engineer he always asks me "how many Abrams tanks I was planning
to support with this?".
--
Robert Allison
Rimshot, Inc.
Georgetown, TX
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Posted by hogheavenfarm on April 24, 2008, 3:10 pm
I have just completed the same thing. Took out a 14' section of wall
(exterior) between the living room and a porch that was added on. I
used engineered (LVL) or as we say Microlam beam built of three
2x12's. Remember this is nominal size, steel isnt. When you get a 9" I
beam , it is 9". A 12" LVL is only 11 1/4" avtual size.
I looked at the "beam-over" pics, good idea, but I was concerned
about the bottom chord of the rafter overlap, looked like only 4-6",
should be more. Others have correctly pointed out, that the posts must
rest on solid bases, all the way down.I'm using 4 2x4's on each side
carrying the load to a double bottom plate which rests directly on the
steel I beam in the basement. If you are doing an outside wall, there
will naturally be something underneath, the problem comes when you
open up an interior wall (load bearing) and post it on nothing. LVL
beams are easier to work with since you can put them up one at a time
and nail them together, no heavy lifting like a steel beam, and no
boxing in problems due to the steel.
For your application a 9" nominal LVL would work, (doubled or
tripled), which would give you the headroom you need.
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Posted by Dave in Houston on April 24, 2008, 3:52 pm
> I looked at the "beam-over" pics, good idea, but I was concerned
> about the bottom chord of the rafter overlap, looked like only 4-6",
> should be more.
What you cannot see in the picture is that the angle iron brackets are
thru-bolted to both sets of ceiling joists, on both sides of the beam.
Others have correctly pointed out, that the posts must
> rest on solid bases, all the way down.
Here's another shot of the new space minus the old wall. The end
support for the beam in this case consisted of four 2X4s, three ganged side
by side in the outside wall cavity and one sistered on the interior side
perpendicular which you can see in the pic.
http://www.pbase.com/speedracer/image/2622654
Dave in Houston
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Posted by Smitty Two on April 25, 2008, 1:46 am
>
>
> > I looked at the "beam-over" pics, good idea, but I was concerned
> > about the bottom chord of the rafter overlap, looked like only 4-6",
> > should be more.
>
> What you cannot see in the picture is that the angle iron brackets are
> thru-bolted to both sets of ceiling joists, on both sides of the beam.
>
> Others have correctly pointed out, that the posts must
> > rest on solid bases, all the way down.
>
> Here's another shot of the new space minus the old wall. The end
> support for the beam in this case consisted of four 2X4s, three ganged side
> by side in the outside wall cavity and one sistered on the interior side
> perpendicular which you can see in the pic.
>
> http://www.pbase.com/speedracer/image/2622654
>
> Dave in Houston
One thing I don't see discussed very often on ahr is sheer strength.
AIUI, houses with a lot of doors and windows often use an interior wall
not only for load bearing, but also for sheer. It's worth considering.
When I added a window and a pocket closet door in the bedroom, I had to
make sheer strength modifications to what was left of the walls.
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