Steel connection elements subject to combined loading?
Steel connection elements subject to combined loading?
(OP)
On page 9-3 in the 13th Edition of the AISC Manual, it is stated "Connection design has been traditionally based on simple stresses, such as shear, tension, compression or flexure, not taken in combination. This simplification is adequate because connection elements are usually small or short enough that an interaction-type distribution cannot form." They follow that up with an explanation involving Von Mises criteria, which doesn't fully satisfy me.
Thoughts? Is everybody neglecting interaction in their connection design?
RAM Connection seems to make this assumption. I guess I like would like to see a little more background information before tacitly accepting this simplification.
Thoughts? Is everybody neglecting interaction in their connection design?
RAM Connection seems to make this assumption. I guess I like would like to see a little more background information before tacitly accepting this simplification.






RE: Steel connection elements subject to combined loading?
RE: Steel connection elements subject to combined loading?
(Vf/Vr)2 + (Tf/Tr)2 <=1
And CSA has another formula for combined shear and tension in slip-critical connections.
BA
RE: Steel connection elements subject to combined loading?
How is it MORE conservative to neglect interaction? Interaction usually reduces your capacity, especially if you are near the stress limit on one state alone.
I should clarify that AISC does consider interaction for bolts similar to the formula you posted. I believe the statement I quoted refers more to connection plates (e.g. a beam web connection plate subject to shear and axial load).
RE: Steel connection elements subject to combined loading?
RE: Steel connection elements subject to combined loading?
if necessary I can still look that one up.
I'm not overly familiar with the eurocodes, but that probably will have something about combined loading too.
However I also recall reading something about max. allowable shear stress not being influenced by any (tensile) preload.
I'll have a look for that publication.
RE: Steel connection elements subject to combined loading?
Also starting at page 10-131 they have a discussion on special considerations for simple shear connections, which discusses some other cases and their appropriate checks.
RE: Steel connection elements subject to combined loading?
EIT
www.HowToEngineer.com
RE: Steel connection elements subject to combined loading?
(Vf/Vr)2 + (Tf/Tr)2 <=1
UK equivalent for bolts in combined shar and tension is
applied shear/shear capacity + applied tension/tension capacity <= 1.4
sorry, can't find the symbols!)
RE: Steel connection elements subject to combined loading?
1) As STRUCTSU10 points out, the 13th edition manual (pg 10-103) gives a method of combined stress interaction for shear and flexure. The method is based on Von Mises criteria and is a bit cumbersome to use.
2) AISC 14th edtion gives an equation (eqn 10-5 on page 10-104) which is a good bit easier to use. Unfortunately, the method does NOT address the presence of axial force in the connection.
3) AISC has somme design examples which may extend this concept out further. Specifically example II.C-5 (which is a chevron brace connection) which shows a direct combination between axial stress and flexure to compare against yielding. I don't like that very much since flexural yielding doesn't necessarily mean that you have achieved failure. They address this by assuming a uniform flexural stress profile (rather than the linear stress profile we normally assume).
4) My personal view is that a general interaction equation can be arrived at by combining items 2 and 3 together... but, only if you look at item three as instead being related to P/Pyield + M/Mplastic. That allows for an easy extension of AISC 14th edition equation 10-5:
Interaction Equation for Flexural, Shear, Axial yielding of a shear tab or gusset plate:
(Vr/Vc)^2 + (Pr/Pc + Mr/Mc)^2
At least, that's what I've decided to do. It's relatively irrelevant for most shear tab connections, but becomes important for vertical brace gusset plates or drag struts where the connection's axial force may be significant.
RE: Steel connection elements subject to combined loading?
You would find:
Normal Stress the the x-z plane: P/A+Mc/I
shear Shear: V/A (approx)
The normal stress on the other planes would be 0. But I guess this is the assumption that is no longer valid?
This seems so basic yet I'm struggling to understand this.
EIT
www.HowToEngineer.com
RE: Steel connection elements subject to combined loading?
For shear-and-axial connections, like a shear tab with axial load, I would combine the axial stress with the flexural stress to size the plate. I would not factor in some interaction with the shear stress.
RE: Steel connection elements subject to combined loading?
It is not basic, bolts present complex mechanical behavior. If you use the theory o solid mechanics that would be correct, but in real world situations there would be plane strain conditions allied with plane stress conditions due to misalignment, yelding of the bolt and the vicinity material and some geometric imperfections.
You can do rough aproaches like adopting criterea as von Mises that does over designing to prevent failure proven kind of effective over the years or you do mechanical testing to asure how much abused your bolts can be. There is no direct and correct way to correlate a combination of tensile/compressive stress and shear stress to the measured yelding tensile stress.
I'd sugest to keep with the code's recomendation and perform some laboratory mechanical testing to be completely safe.
Sorry if the message is unclear. English is not my first language and I find it challenging to discuss engineering related subjects in english.
RE: Steel connection elements subject to combined loading?
Abpark - Sorry don't mean to threadjack.
EIT
www.HowToEngineer.com
RE: Steel connection elements subject to combined loading?
It certainly seems like a general statement to me. They really should clarify it if this is the case.
I guess I should I see if I can find a worked out shear-and-axial beam connection and see how they handle interaction. I'm curious.
RE: Steel connection elements subject to combined loading?
RE: Steel connection elements subject to combined loading?