> From: Matthew Jordan <MattJ(--nospam--at)CRJARCH.com>
> To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
> Subject: RE: unbraced comp flange
> A curios situation: Can you have a WF beam with a completely unbraced
> compression flange? A WF sits on top of a column at each end and has plate
> supported on the bottom flange and loads hung off the bottom of the beam.
> nothing attaches to the top. Is this even allowed? The only way lateral
> buckling is resisted is by bending of the web as the bot. flng is held in
> place by the ceiling plate. Is that ok?
> matt jordan
Two separate issues:
1) buckling of the compression flange in bending,
2) general instability of the assembly relative to the load/reaction
positions and vectors.
If the beam is adequate for unbraced length of the compression flange
and there are no loads fastened above the bottom flange of the beam then
the assembly has a level of inherent stability.
Increasing load and/or increasing eccentricity above the bottom flange
leads to greater instability. Load attached to clip centred beneath the
bottom flange causes self-righting moments if the top flange moves away
from vertical centre.
There is some rotational resistance in the flange/web. This can be
increased with web stiffeners at load and/or reaction points (the post)
or by additional bracing. Mileage may vary.
There are limits.
Paul Ransom, P. Eng.
Burlington, Ontario, Canada