Perpendicular Beam to Brace Against Web Crippling
Perpendicular Beam to Brace Against Web Crippling
(OP)
When a beam frames over the top of a column, web crippling is typically checked. In the situation where a girder frames over the top of the column and beams frame into the side of the girder, can the beam to girder connection be considered to "brace" against web crippling or to reduce the effective height "h" of the girder?






RE: Perpendicular Beam to Brace Against Web Crippling
BA
RE: Perpendicular Beam to Brace Against Web Crippling
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RE: Perpendicular Beam to Brace Against Web Crippling
Alternatively, a single plate stiffener could be considered each side of the girder as suggested by JAE, perhaps with a thicker cap plate over the column.
BA
RE: Perpendicular Beam to Brace Against Web Crippling
Thanks again!
EIT
www.HowToEngineer.com
RE: Perpendicular Beam to Brace Against Web Crippling
Whether or not web crippling is an issue, it is good practice to provide a stiffener in the girder to provide racking stability.
BA
RE: Perpendicular Beam to Brace Against Web Crippling
Anybody have an idea on why the limit state is a function of "d" if the crippling occurs only locally (beneath the load - not across the entire "d" ).
Also what I don't understand is why tf is in the equation at all?
RE: Perpendicular Beam to Brace Against Web Crippling
BA
RE: Perpendicular Beam to Brace Against Web Crippling
RE: Perpendicular Beam to Brace Against Web Crippling
Looks after web crippling and maintaining the section for post elastic deformation... and a multitude of other sins...
Dik
RE: Perpendicular Beam to Brace Against Web Crippling
1) Analytically, you're dealing buckling on a yield line mechanism like that shown below per Deker.
2) For plate girders, the 2 x alpha dimension is 50 tw. That's pretty tall. I don't know if that holds exactly for non-plate girders but the take away, I think, is that you're looking at buckling over a substantial depth. Probably almost the entire beam depth in a lot of cases.
3) Anything that interrupts the buckling mechanism shown below is going to help some. Anything.
4) I don't know that it is necessary to start the stiffener reinforcing from the very bottom of the web. The purpose of the stiffener, for this one failure mode, is not load delivery but, rather, out of plane web bracing. A stiffener doesn't necessarily need to bottom out to get that done in my opinion.
5) In my opinion, a pair of angles tightly bolted and spanning most of the beam depth almost certainly disrupts the buckling pattern that is web crippling. Of course, to make that argument, you have to go off reservation a bit which requires some risk tolerance and a willingness to expend effort that may not be commensurate with your fee.
6) One alternate reinforcing scheme that would involve less head scratching would be to place half height vertical stiffeners either side of the secondary beams. I don't know your exact proportions but I have a hard time envisioning a practical arrangement for which that would not work.
7) A second alternate reinforcing scheme, space permitting, would involve the use of longitudinal stiffeners to disrupt the presumed buckling pattern. Some googling will turn up some papers on that. Medium head scratching.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Perpendicular Beam to Brace Against Web Crippling
Interesting to note that the 2016 Manual states that the stiffener must be 3/4 depth whereas the 2010 only required half-depth.
@Deker: Thanks for the reference.
@KootK: In general I agree with your input, a few questions comments:
2.) I question this. Although the equations seem to indicate that the entire height is involved in the capacity, according to the AISC commentary the buckling only occurs in a portion of the web directly adjacent to the loaded edge. So part of me says "the height should not affect web crippling based on what my eyes see", but the other part of me says "this is probably a higher mode of buckling which is still dependent on the total height".
3.) Agreed
4.) Same response as item #2). "By inspection" I want it directly attached to the loaded flange, "mathematically" I could see that it should matter.
5.) Agreed, just not sure how to put numbers to this.
6.) Also Agreed
7.) I'm a little leery of this one as well due to my comments in item #1.
Here is the commentary:
EIT
www.HowToEngineer.com
RE: Perpendicular Beam to Brace Against Web Crippling
Looking at that makes me question why bf isn't included in the equation. And I still don't understand why d is in the equation. Except to possibly be used as an upper-bound on the two alpha parameter, it doesn't seem to come in to play at all.
RE: Perpendicular Beam to Brace Against Web Crippling
Interesting point. Maybe it's only a part of the flange near the web that really participates so more based on tf/tw ratio? Just guessing/intuiting.
I question it too, really, despite having seen it in print.
Although the lion's share of the lateral displacement happens near the loaded flange, I think that the level of rotation restraint provided to the other end of the buckling web segment is still very much a function of the entire web depths. That's my speculation at least. I think that would jive with depth being and inverse linear parameter.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Perpendicular Beam to Brace Against Web Crippling
RE: Perpendicular Beam to Brace Against Web Crippling
BA
RE: Perpendicular Beam to Brace Against Web Crippling
I also would have thought this would increase the crippling capacity, but I just read this which seems to suggest otherwise:
Would you mind sharing the source of Fig. 1 that you posted above? I'd like to see if it would be worth getting as a reference.
RE: Perpendicular Beam to Brace Against Web Crippling
RE: Perpendicular Beam to Brace Against Web Crippling
Of course. These be my sources. There are derivations of the crippling math in there.
Link
Link
Interesting. What I take from that is that the 0.20 - 0.25 high longitudinal stiffeners commonly provided to address shear buckling and flexural compression web buckling don't extend low enough to do much about crippling. So, again, it all comes back to how tall that buckled chunk of web is. The photo below is from the Rockey paper. Looking at that, I'd have a pretty tough time accepting that suitably located longitudinal stiffeners wouldn't help. As shown in the picture, they would reduce the height of the buckling. I'd think that capacity would go up in proportion to the squared inverse of that reduction.
Practically, of one need to span the longitudinal stiffeners between two vertical stiffeners, then using the two vertical stiffeners alone would seem the logical choice.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Perpendicular Beam to Brace Against Web Crippling
KootK - Great references, thanks for sharing. The longitudinal stiffeners in the Elgaaly and Salkar tests actually were placed near the top flange (loaded flange) at distance of 0.2d, while the crippling occurred within a height of 0.16d. But your point stands, and I agree that a well-placed longitudinal stiffener (25tw from the loaded flange?) would have to increase the crippling capacity. Also agree that for OP's condition the two vertical stiffeners alone seem the most practical. I thought this bit from your second reference was interesting on how bf was removed and d was inserted into the crippling equations:
RE: Perpendicular Beam to Brace Against Web Crippling
That is interesting. And it answers Cal91's question I believe. I can't claim to actually grasp the physical significance though, I'm afraid.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.