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'[EE]: Best place to weaken a beam'
M. Adam Davis
Simply placing reinforcing OSB over the slot is not likely to replace
the functionality of the top fibers of the beam.
You might consider replacing the board with a steel beam that is not
tall, and then placing wood between the beam and floor for fastening
and support, except where you want the 'slot':
Underscore = floor
w = wood
S = steel beam
Alternately replace the hypothetical beam with wood - you'll need a
wider beam of wood, though. I don't know what the loading factor is,
but for instance you might find that 2 2x8's equal the capacity of
one 2x10, though there will be greater flexing.
We could give you more detailed answers (or alternatives) if you tell
us what the slot is for.
On 10/10/07, Cedric Chang <nope9.com> wrote: cc
Peter Todd <petertodd.ca> wrote: pete
> On Thu, Oct 11, 2007 at 10:00:22AM -0600, Cedric Chang wrote:
> > I really appreciate the replies and will let you all know what I do
> > and what happens.
> > One further comment: I have a lot of faith in OSB since I have seen
> > many I-beams built out of them.
> I have a lot of respect for engineers because they manage to build I-beams
> out of OSB. :)
The engineered I-beams I've seen use OSB for the "webbing" between the top
and bottom rails. The real strength of the beam is in the rails, which are
usually solid wood. The webbing just keeps them parallel, and resists the
compressive load across the height of the beam, which requires relatively
As everyone else has said, the answer is generally "within the center 1/3
of the height, and not near any other weakenings".
-- Dave Tweed
|Since OSB is a relatively new product, I haven't needed to become
familiar with it's properties, and therefore can't say anything about
it. But, since there are less parallel fibers in a particular direct, I
think we can say that it's allowable tensile strength is going to be
less than that of the parent wood specie. Note that plywood has a lower
allowable bending when the span is perpendicular to the face grain
And yes, if the depth of the beam is less the deflection (springy) will
be significantly more since the factor is now the 4th power of the
depth. If you can throw enough width at it, you might be able to have
the strength and stiffness, but somewhere the actual weight of the beam
will become great and not even carry it's own weight. And steel is
flexible and has limitations too.
The answer to this problem is beyond the scope of this list, and should
(must) be left to professionals that can assure that safety will prevail
with no loss of life, injury or damage to property. :) This not like
trying some electronics, where it is no big thing if a 2n2222 transistor
was undersized amperage, blows, and just solder in another or replace
with a beefier part. :(
I like the definition of Engineering: "The economic application of
scientific principles." :)
M. Adam Davis wrote:
More to it than that, take a thick magazine or book, and bend it, while
allowing the pages to slide against each other. Then bend again,
squeezing the ends of the pages together sufficient to prevent sliding,
and notice how stiff the book is. This is called shear flow, and the web
of the beam must resist this also, and the glued joint is designed for
this force. The maximum force of this shear flow at the end of the beam
is at the mid height. These subjects are covered in 1st semester of
mechanics of materials class, just like Ohms law is covered in 1st EE
Dave Tweed wrote:
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