Interpretation on AISC Weld Strength 2

[theonlynamenottaken]

In reading AISC 360-05 (13th Edition) I'm a bit confused on Chapter J: Design of Connections, section J2.4 Weld Strength. After the basic Rn=FwAw equation there's a statement, "Alternatively, for fillet welds loaded in-plane the... strength... is permitted to be determined as follows." It then goes on to a section outlining the three alternative cases for fillet weld strength, where one can use a 50% strength increase for transversely loaded fillets:
a) linear weld group loaded in-plane through center of gravity
b) weld group that is loaded in-plane and analyzed using an instantaneous center of rotation method
c) fillet weld groups concentrically loaded and consisting of elements that are oriented both longitudinally and transversely to the direction of applied load.

The majority of welds I work with are loaded normal to faying surface; e.g. an eccentric compressive load. So, I have no in-plane load components, just out-of-plane tension and compression.

Can I not take advantage of the 1.50 increase for fillet welds loaded transversely? The blanket statement I quoted above does say "fillet welds loaded in-plane".

My specific, simplified problem: Circular fillet weld, E70xx, 6.63" pipe diameter, 4.6k ultimate compressive force with 78" eccentricity. Pipe being welded to face of flat plate.
Mu = 359 k"
S(@w=1.0) = 38.5 in3 (assuming 3/8" weld size)
Rmax = 9.11 k/in (including reduction from axial compression)
Rnw = 22.27 k/in (without 1.50 increase)
= 33.40 k/in (with 1.50 increase)
w = .41" => 7/16" (without 1.50 increase)
= .27" => 5/16" (with 1.50 increase)

Your thoughts?

 

[WillisV]

The intent was not to prevent you from using the 1.5 for fillet welds loaded transversely, and in the 2010 Specification the words "in-plane" have been removed from this section.

 

[metengr]

The intent was not to prevent you from using the 1.5 for fillet welds loaded transversely,...

Whose intent or interpretation? If there is a question about interpretation I would submit a technical inquiry for a final response.

http://www.modernsteel.com/steelinterchange_details.php?id=650

 

[WillisV]

The intent of the Specification Committee - that's why it was revised for 2010 - however I agree that might not be good enough for a picky building official so it never hurts to ask the solutions center as metengr is suggesting.

 

[theonlynamenottaken]

Advice heeded. I submitted my question to AISC Solutions Center this morning, albeit worded more generally:

Answer: (which appeared in my inbox within three hours...)

The prohibition against using the directional strength increase with out-of-plane has been in the Specification for quite some time. However, for as long as the strength increase has been allowed, the Manual has used the strength increase with out-of-plane loadings in both examples and Tables (for instance the special case with k=0 in Table 8-4 of the 13th Edition). Somehow this discrepancy was not picked-up, and many structures have been designed using the strength increase in conjunction with out-of-plane loading.

The concern with out-of-plane loads was that the welds may not have the same ductility as when loaded in-plane. Since we did not have the data to justify the directional strength increase, out-of-plane loadings were excluded from this provision of the Specification. As we worked on the 2010 Specifications, AISC completed research to settled the issue. Fortunately, the testing indicated that the use of the directional strength increase is justified with out-of-plane loading, so this restriction has been removed from the 2010 Specification.

Strictly speaking, the use of the directional strength increase is prohibted with out-of-plane loads in the 2005 Specification, though there is no longer any technical basis for this and it is contrary to common design practice. Now that you have all the information, you can apply your own judgement as to whether or not to use the directional strength increase with out-of-plane loading between now and the release of the 2010 Specification.

Larry S. Muir, P.E.
Consultant
American Institute of Steel Construction