Width to Thickness Ratio
Width to Thickness Ratio
(OP)
I am analyzing an old built-up girder made with a web plate and pairs of equal leg angles for the top and bottom flanges.
It is quite a sizable girder (about 7' deep) but only has a 7/16" web.
I was wondering how out of line it would be to check the web slenderness h/tw according to AISC chapter B, by taking the height between the toes of the flange angles rather than the clear flange distance. The angles are 8x8's. If I checked the web between the vertical toes it would reduce the "h" value 16".
I cant see the web buckling where it is sandwiched in between the flange angles.
Anyone have any thoughts?
It is quite a sizable girder (about 7' deep) but only has a 7/16" web.
I was wondering how out of line it would be to check the web slenderness h/tw according to AISC chapter B, by taking the height between the toes of the flange angles rather than the clear flange distance. The angles are 8x8's. If I checked the web between the vertical toes it would reduce the "h" value 16".
I cant see the web buckling where it is sandwiched in between the flange angles.
Anyone have any thoughts?






RE: Width to Thickness Ratio
RE: Width to Thickness Ratio
You don't know of any code provisions qualifying something like this, do you?
This just doesn't fall neatly into AISC's nice little examples chart in Chapter B of the spec.
I have wondered about this in the past too. This job has several girders like the one I described and I am trying to avoid the dreaded slender elements provisions if possible.
If it has to be done, so be it
RE: Width to Thickness Ratio
RE: Width to Thickness Ratio
Back to the original question though....don't you think that using the distance between the angles is more in keeping with the intent of "limiting width-thickness ratios" as they are stated in the code?
RE: Width to Thickness Ratio
The angles can bend under a buckled web condition to some extent right? This is analogous to the stepped column situation for bridge crane columns where the lower section of column is deeper than the upper section of column and the engineer wonders...what's the real k value and what I should I use?
RE: Width to Thickness Ratio
In this case the each angle is twice the thickness of the web...(7/16 web sandwiched between 7/8" angles).
JAE- I take it you have had the fine pleasure of going through figuring out K-factors for stepped columns....quite fun eh?
RE: Width to Thickness Ratio
RE: Width to Thickness Ratio
I analyze them quite often...thankfully I have some FEM techniques handed down to me from some guys who helped write the Mill Bldg spec that make them a little bit easier.
I agree...I like an independent crane shaft.
RE: Width to Thickness Ratio
RE: Width to Thickness Ratio
RE: Width to Thickness Ratio
RE: Width to Thickness Ratio
RE: Width to Thickness Ratio
In the glossary?
RE: Width to Thickness Ratio
RE: Width to Thickness Ratio
On a side note, regarding JAE and ToadJones's discussion about stepped columns, there's an article by Suresh T. Dalal named "Some Non-Conventional Cases of Column Design" that gives guidance into determining buckling loads for stepped columns. Dr. White at Georgia Tech also has an AISC Design Guide coming out soon that talks about designing with web-tapered members (such as PEMB frame configurations).
Structural Design Engineer
New York, NY
RE: Width to Thickness Ratio
Dik