Instanteous Center of Rotation Help
Instanteous Center of Rotation Help
(OP)
I was comparing Blodgett's method for analyzing stress in a weld to determine capacity compared to the AISC tables for a weldment group.
I get a large discrepancy. This isn't for a job or anything, just something I was doing on the side when bored. Anyone else that's more familiar with this can point out what's wrong?
I made a mathcad sheet for blodgett's method and did a quick check using the AISC table at the bottom and compared the two. attached
whatever is wrong I don't see it. Is it Jw? not sure
Thanks
I get a large discrepancy. This isn't for a job or anything, just something I was doing on the side when bored. Anyone else that's more familiar with this can point out what's wrong?
I made a mathcad sheet for blodgett's method and did a quick check using the AISC table at the bottom and compared the two. attached
whatever is wrong I don't see it. Is it Jw? not sure
Thanks






RE: Instanteous Center of Rotation Help
I should have set Lt=0
attached with Lt = 0
RE: Instanteous Center of Rotation Help
RE: Instanteous Center of Rotation Help
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: Instanteous Center of Rotation Help
RE: Instanteous Center of Rotation Help
RE: Instanteous Center of Rotation Help
RE: Instanteous Center of Rotation Help
RE: Instanteous Center of Rotation Help
http://www.steeltools.org/resources/viewdocument/?...
RE: Instanteous Center of Rotation Help
I'm at a disadvantage as my AISC manual is at home. I'll check it out tonight. There is a a subtle difference between ductility and plasticity. If our welds truly went plastic, there would be permanent set.
I don't think so. It's a numerical procedure that is not based on plastification as sbisteel has alluded above. If you make a spreadsheet using the modern non-linear method, and then switch your force-deformation relationship to be linear, you'll get Blodgett's results.
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: Instanteous Center of Rotation Help
Also, found this article Link
I shall read.
RE: Instanteous Center of Rotation Help
Regarding plastic vs. ductility - ductility is by defined by a materials ability to move past linear elastic behavior. What that means to me is plastic behavior. It doesn't necessarily mean permanent deformations until you get to the ultimate strength level. It's to a beam. It's elastic under service loading, but at ultimate strength is counting on the plastic strength of the section.
RE: Instanteous Center of Rotation Help
RE: Instanteous Center of Rotation Help
@Lion: sorry about the misquote. iPhone copy/paste abuse. Regarding our debate:
1) plasticity = fibers yielding = some degree of permanent deformation. This is true even when only part of a section plastifies.
2) you can be non-linear -- and ductile -- without yielding any fibers. Just ask a rubber band.
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: Instanteous Center of Rotation Help
RE: Instanteous Center of Rotation Help
Something I noticed though, none of the articles I have read talk about a double eccentricity such as a single angle connection to a beam. I modified blodgett's to include it. Any thoughts to why this is?
RE: Instanteous Center of Rotation Help
It seems that a rubber band is:
1) Non-linear.
2) Ductile.
3) Elastic? I'm not really sure.
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: Instanteous Center of Rotation Help
a) because it's hard.
b) for that particular example, you'd normally assume that angle flexibility eliminates eccentricity in the one direction.
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: Instanteous Center of Rotation Help
That stress-strain curve does not look at all like a ductile material to me.
I don't really care about the elasticity/ductility of a rubber band.
I'm struggling to think of a material that doesn't undergo permanent deformation as ductile, regardless of the nonlinearity of the elastic deformations. S&J defines ductility as the amount of permanent strain (i.e. strain exceeding proportional limit) up to the point of fracture. The very nature of ductility in this context requires permanent strain (i.e. plastic deformations).
RE: Instanteous Center of Rotation Help
RE: Instanteous Center of Rotation Help
I agree. That's part of what makes the single bolt, single angle connection a bit sketchy and only suitable for light loads.
It's not. It's hard for the modern AISC method. These kinds of situations are precisely why I still use the Blodgett method myself, as I mentioned above.
@Lion: you've made some thought provoking points. I'll need to think on it.
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: Instanteous Center of Rotation Help
@Jerehmy: The Gaylord, Gaylord, and Stallmeyer textbook ("Design of Steel Structures", third edition) indicates it "usual practice" to design the outstanding leg connection (the angle leg not attached to the beam web) to fully resist the out-of-plane moment that I believe you are questioning.
RE: Instanteous Center of Rotation Help
RE: Instanteous Center of Rotation Help
I now believe that some of the statements that I made above were wrong. Having consulted my college material science textbook and some other sources, here's my current understanding of things:
1) Ductility is a subset of the plasticity phenomenon which also includes malleability. Ductility involves plastic behaviour and permanent deformation.
2) Depending on how things shake out in the IC analysis, some weld segments may indeed plastify. So a weld group can often be said to be partially plastic at design capacity.
3) In the case of a circular arc fillet weld with its focal point at the IC, the entire weld may plastify before reaching its ultimate strength.
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: Instanteous Center of Rotation Help
Mn = Σ[FnwiyAwei(xi) - FnwixAwei(yi)]
is the subtraction of the x component because the x and y stress vectors will always be opposite in sign?
RE: Instanteous Center of Rotation Help
RE: Instanteous Center of Rotation Help
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.