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RE: RISA, Lb-comp top and bottom[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: RISA, Lb-comp top and bottom
- From: "Polhemus, Bill" <BPolhemus(--nospam--at)wje.com>
- Date: Thu, 16 Feb 2006 14:15:52 -0600
Yeah, it’s actually referring to the “physical bottom” flange of the beam.
One thing that I think a lot of student- and graduate-engineers have to learn to do when they get out into the working world, is “relearn” a lot of nomenclature. When you’re in school, you’re typically looking at a lot of abstracts—which is an appropriate way to learn fundamental concepts.
However, out in the real world, we tend to call things according to their actual, real-life function instead of according to theoretical concepts.
Therefore, we think of the “bottom flange” of a beam as being JUST THAT: The flange on the underside, that we have to worry (sometimes) about bracing! :0)
And yes, your description of a “kicker” is exactly correct. Good for you.
Want a job? ;-)
From: john smith
So, Lcomp-bottom doesn't
mean the bottom of the compression area of the beam (ie. upper half of depth of
the beam, the bottom half being in tension)? But the bracing length for
the bottom of the beam.
On 2/16/06, Polhemus, Bill <BPolhemus(--nospam--at)wje.com> wrote:
Welcome to the wonderful world of structural engineering.
The "bottom" and "top" distinctions are important for beams where you have 'reverse curvature' bending. That is, you have both "positive" and "negative" bending moments in a single beam.
If you have steel roof joists bearing on the beam—and assuming the joists themselves are securely in place, having e.g. a roof deck attached—the Lb-top is going to be the spacing of the joists.
For the bottom chord, if you have no "kickers" from any of the joists, the Lb-bottom is going to be the full span between beam supports. However, if you DO have "kickers" that securely support the bottom flange to the joist framing, then the distance from the farthest support will be Lb-bottom.
Hope that's clear.
i'm new to the listserve and am currently and engineering student.
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