Bracing Compression Flange for Lateral Torsional Buckling 3

[vcomguy]

Can a web stiffener in a WF Beam or Column be considered to provide bracing for Lateral Torsional Buckling of the "compression" flange?

The concern is that the whole section of the WF in the plane of the web stiffener may tend to rotate, unless the "tension" flange is rigidly restained by another framing member such as a wall girt in the case of a wall column.

 

[WillisV]

No.

 

[JAE]

No..

 

[hokie66]

There has been some recent research, I believe by HERA in New Zealand, that shows that web stiffeners do adequately brace the bottom flange of rafters in uplift situations, provided the connection of the purlins to the top flange is stiff enough. I think this was posted some time ago by YoungStructural. I would try searching the site, and perhaps YS will see this thread and assist.

 

[WillisV]

hokie66 - yes it is certainly possible to brace the opposite flange through stiffeners provided the other flange has some restraint (purlin, other framing member, etc). I believe the OP was asking if the simple act of adding web stiffeners to a beam with no other framing members will introduce a bracing point - in that case a definite no.

 

[hokie66]

Yes, I certainly agree. But he was asking about a bending member, and he mentioned a wall girt which could conceivably restrain the rotation. I may have misinterpreted, as I thought he was asking whether stiffeners could be used instead of diagonal "fly braces". Maybe the OP will check back in.

 

[vcomguy]

My original description stated:

The concern is that the whole section of the WF in the plane of the web stiffener may tend to rotate, unless the "tension" flange is rigidly restained by another framing member such as a wall girt in the case of a wall column.

Perhaps if I can clarify:

...plane of the web stiffener may tend to rotate about the neutral longitudinal axis of the member, unless...

I believe the concept is to stabilize the "free" column flange that is not connected to a purlin or girt. The other question arises, how stiff is the connection between the "girt" and column flange? Is it stiff enough to restrain the flange and the twisting of the web in the column?

A load reversal could change a column flange force from tension to compression which might require "bracing" of the flange opposite a wall girt as an example.

I'm trying to help out a friend, and don't have anything more specific. I was attempting to identify a reference to allow or not allow this based on one of our steel codes.

Thanks for your input and interest.