Beam Web Stiffeners

[Fracball]

Hi:

I’ve got a W beam with the top flange subjected to a compressive load that’s distributed over the length of the beam, and I am checking to see if web stiffeners are needed. The ends of the beam are restrained from rotating. I’ve checked for web yielding and web crippling per 9th edition of AISC ASD, and web stiffeners are not needed per these criteria.

I assumed that a check for local flange bending was not needed since my beam is compact and since the limiting width-thickness ratio is not exceeded.

1. Is this assumption correct?
2. If the assumption is not correct, do I need to check for local flange bending?
3. What is the criterion for checking local flange bending?

Thanks

 

[austim]

fracball,

If the 'local flange bending' to which you refer is the transverse bending (ie the flange acting as balanced cantilevers about the top of the web), then your stated assumption is incorrect, and you do have to check for it.

Whether a section is compact or not, and the matter of width/thickness ratio is directed only at the longitudinal bending stresses. (If a flange outstand is too thin, then you cannot assume that the full flange area is effective in resisting 'global' bending of the beam).

 

[trainguy]

What is loading the top flange? A deck, wall, etc. please clarify. Usually, local flange bending checks are unwarranted, since whatever rests on your beam directly "finds" the beam web, unless you are really loading the edges of the top flange. Web stiffeners are commonly used for other reasons than your case, such as web crippling due to CONCENTRATED loads, or at support reaction points. You seem to want to use them as FLANGE stiffeners, instead of web stiffeners...

 

[Fracball]

trainguy:

The dead and live weight (approx. 1000 klbf max.) of a piece of equipment will load the top flange of the beam. The load is distributed over a beam length of about 15 feet. My beam (W24x55) is being used as a support for this equipment. The footing of this equipment is such that the load will not be entirely directed into the web. You are correct, my main concern is flange stiffening instead of web stiffening. Thanks for your comments.