W shape loading?
W shape loading?
(OP)
I have a large W shape as my beam with 6X14 timbers (rafters) every 2' on both sides of the beam, each timber has a 6k reaction. The owners want to place these rafters on the bottom flange of the beam. I've never done that, all I've ever seen is the rafters or joists bearing on top of the beam (top of the top flange). Are W shapes designed such that one can load it an any shape or form or do I need to do some other kind of check. the loading will be equal on both sides so the torsion will be small. Any advice would be great. Thanks






RE: W shape loading?
RE: W shape loading?
RE: W shape loading?
RE: W shape loading?
DWHA- How do you figure that?
RE: W shape loading?
RE: W shape loading?
RE: W shape loading?
RE: W shape loading?
In any new design I ignor it. But if there is an existing structure that has bott flange loading, I will utilize it if needed.
RE: W shape loading?
You might want to check them out
RE: W shape loading?
This only applies if LTB controls. For a section adequately braced to develop phi Mn, it makes no difference where the load is. Additionally, you are ignoring that fact that by moving the joists and, consequently, the bracing to the bottom flange, you now have an unbraced compression flange (assuming a simply supported beam)
RE: W shape loading?
How would you even utilize the increase? Would you dig into research papers to find a more exact buckling moment?
RE: W shape loading?
RE: W shape loading?
RE: W shape loading?
"For a section adequately braced to develop phi Mn, it makes no difference where the load is"-Correct
"Additionally, you are ignoring that fact that by moving the joists and, consequently, the bracing to the bottom flange, you now have an unbraced compression flange (assuming a simply supported beam)"- Incorrect
I stated that if LTB bracing was the same, and never said that LTB did not control.
You are assuming that the rafters are connected to the top flange. The OP did not state that therefore, it may (not definatly) give additional capacity. That is for TonyES to determine.
RE: W shape loading?
What do you mean it will not affect the allowable capacity. Do you mean it will not affect the plastic capacity? I will agree with that.
Isn't 99% of what we do based on theory? Why are you arguing with it now.
When I used this, I prevented a factory from being shut down for period of time. The factory saved a lot of money due to the fact that they did not loose production during this time.
RE: W shape loading?
RE: W shape loading?
The "Guide to Stability Design Criteria for Metal Structures", 5th edition, provides methods to account for the location of the load relative to the shear center for several common loading conditions. See pages 194 to 197. I have successfully used this method in the past when evaluating the capacity of existing members. The method contained in the Guide is a "more precise analysis" in my opinion.
Hokie93
RE: W shape loading?
Mike McCann
McCann Engineering
RE: W shape loading?
As noted above you will then have no lateral restraint to the top flange, so I usually call up say 2"x1/4"x1' long straps each side bolted to every 4th joist which ties the beam into the floor diaphragm (via the flooring nails). Then check the beam for that effective length.
RE: W shape loading?
RE: W shape loading?