Localized Buckling of a built-up shape 3

[WARose]

I’ve been asked to look at an angle that is made up of two plates [each 1.25”x20”] welded together. For the purposes of calculating allowable stresses, I am checking it by the 13th edition (of AISC). One thing that concerns me though: is this code even applicable? You look at the largest angle in the manual and it’s about an 8”.

So [to start off with] you check localized buckling by the values in Table B4.1 and it exceeds the compact limit but not the noncompact limit....but you wonder: is this applicable? Is there some other buckling mode outside the scope of this manual that may control? Thoughts?

 

[JStephen]

I don't think the physical size itself would be an issue. However, rolled angles normally have a fairly generous fillet radius on the inside that likely isn't duplicated on a built-up section, so I would be a bit leery assuming that the standard angle-design procedures were strictly applicable to it.

 

[WARose]

Thanks for the feedback JStephen.

 

[rb1957]

what sort of shear and tension forces are being carried by the weld ?

 

[WARose]

rb, are you asking for magnitude or type?

 

[dhengr]

Table B5.1 deals with Width-Thickness Ratios for, outstanding unstiffened compression elements and localized buckling of these elements when they are part of an entire column member. Your angle legs are stiffened on one edge and not on the other edge. Of course, you still have to look at the entire member and study its potential to buckle as a full length member or as a braced member; kl/r, end conditions and all that good stuff. By using AISC sections B and E you hone in on the critical condition. But, AISC still doesn’t cover every possible/conceivable steel detail in the world, so we’re still sometimes left to our own devices, experience and judgement.

Look at such texts as:
** “Guide to Stability Design Criteria for Metal Structures,” 3rd. Ed., Edited by Bruce G. Johnson. I believe this has several later eds. and is now edited by T.V. Galambos, pub. by Wiley.
** “Buckling Strength of Metal Structures,” by Friedrich Bleich, pub. by McGraw-Hill.
** “Theory of Elastic Stabilty,” by S.P. Timoshenko and J.M. Gere, pub. by McGraw-Hill.
** “Theory of Elasticity,” by S.P. Timoshenko and J.N. Goodier, pub. by McGraw-Hill.
** and many others.

rb was asking for enough pertinent engineering info. so we could really visualize and understand the problem. What are the loads, is it 2' long or 20' long? What are the loads, and how is it loaded? What are the end conditions, any bracing? All info. needed to start to solve your problem.

 

[WARose]

rb was asking for enough pertinent engineering info. so we could really visualize and understand the problem. What are the loads, is it 2' long or 20' long? What are the loads, and how is it loaded? What are the end conditions, any bracing? All info. needed to start to solve your problem.

The situation (in its entirety) is a bit long to lay out…..the aspect of it that worried me is what I posted…..the rest is fairly straight forward. I went ahead and treated it by the 13th edition…....which seems appropriate. I have some of the references you cited on the shelf but I thought I’d ask here on the off chance someone had run into this themselves and felt one code was more applicable to this than another.

Thanks to all who replied.