Fillet Welds in OMF
Fillet Welds in OMF
(OP)
I am looking at designing an OMF per AISC 341-05 Section 11. This will be the first time I do a full blown design to 341 and I have a few questions I would appreciate any input on.
I have an exterior pipe rack in SDC D (non-building structure similar to buildings) designed to R=3.5 (using ASCE 7-05 table 15.4-1 note "d" for acceptance). I cannot use a lower R value otherwise the foundations get huge.
I plan on designing the connections per sections AISC 341-05 11.2a, 11.2c and 11.5 as opposed to using a prequalified SMF or IMF connection per AISC 358.
Q1: Can a double sided fillet weld be used as the FM moment connection between the beam and column flange?
Referencing 341 section 11.2a requirement number (3) indicates required strengths for double sided PJP and double sided fillet welds, which leads me to believe fillet welds are acceptable for OMF's.
Q2: If a fillet weld can be used, does it have to be demand critical?
Section 11.2c indicates only CJP's for OMF's to be demand critical so I would assume fillet welds do not need to be.
Q3 (Hypothetical maybe): Say a PJP weld was being used that was demand critical, since this is an exterior application, say 0deg F is the lowest anticipated service temp (LAST) per section 7.3b a qualified weld filler material to be used would have to be in accordance with 341 Appendix X for 0deg +20deg = 20 deg F for the notch toughness test. How is this accomplished?
Can the design document specify the required temperature and a filler material be purchased by the fab shop that already has been tested per Appendix X requirements? Does the fab shop performing the welding need to perform the verification test?
Q4: 341 section 5.1 Structural design drawings, How does one identify the SLRS members on a drawing?
I do not believe I have ever seen this done before and do not know if this is done in a typical or standard way. Can this be as simple as putting an "*" by the member sizes in the SLRS and adding a note explaining the "*" is part of the SLRS. Similarly for the connections and demand critical welds, can this be accomplished with an "*" or "SLRS" note pointed to each of the connections and welds.
Appreciate any / all input and comments. Thanks
I have an exterior pipe rack in SDC D (non-building structure similar to buildings) designed to R=3.5 (using ASCE 7-05 table 15.4-1 note "d" for acceptance). I cannot use a lower R value otherwise the foundations get huge.
I plan on designing the connections per sections AISC 341-05 11.2a, 11.2c and 11.5 as opposed to using a prequalified SMF or IMF connection per AISC 358.
Q1: Can a double sided fillet weld be used as the FM moment connection between the beam and column flange?
Referencing 341 section 11.2a requirement number (3) indicates required strengths for double sided PJP and double sided fillet welds, which leads me to believe fillet welds are acceptable for OMF's.
Q2: If a fillet weld can be used, does it have to be demand critical?
Section 11.2c indicates only CJP's for OMF's to be demand critical so I would assume fillet welds do not need to be.
Q3 (Hypothetical maybe): Say a PJP weld was being used that was demand critical, since this is an exterior application, say 0deg F is the lowest anticipated service temp (LAST) per section 7.3b a qualified weld filler material to be used would have to be in accordance with 341 Appendix X for 0deg +20deg = 20 deg F for the notch toughness test. How is this accomplished?
Can the design document specify the required temperature and a filler material be purchased by the fab shop that already has been tested per Appendix X requirements? Does the fab shop performing the welding need to perform the verification test?
Q4: 341 section 5.1 Structural design drawings, How does one identify the SLRS members on a drawing?
I do not believe I have ever seen this done before and do not know if this is done in a typical or standard way. Can this be as simple as putting an "*" by the member sizes in the SLRS and adding a note explaining the "*" is part of the SLRS. Similarly for the connections and demand critical welds, can this be accomplished with an "*" or "SLRS" note pointed to each of the connections and welds.
Appreciate any / all input and comments. Thanks






RE: Fillet Welds in OMF
1) Yes, I do believe a double-sided fillet weld can be used. I've never done it but it's allowed.
2) Yes, Fillet welds are not required to be demand critical -- I am not sure the reasoning for this as it was my understanding that whenever the failure of a connection results in the failure of LFRS that it should be demand critical weld. I'm assuming that it is only because Fillet Welds are only allowed for OMF and therefore are not expected to have the same level of ductility as a IMF or SMF.
3) I'll let someone else answer this as I'm not entirely sure. However I don't believe that the PJP weld needs to be demand critical in an OMF.
4) I think that most of these are handled with general notes / details of your lateral elements. Typically, for a moment frame I'll show the moment symbol (and have that shown in the legend) at the end of the beam and then draw an elevation of the frame as well. The elevation will then reference the moment connections in detail. The demand critical welds would typically be called out in general notes or on the moment frame detail. I don't think you need to add a "*" next to your beam to say its part of the moment frame, but it also wouldn't hurt if you wanted to.
RE: Fillet Welds in OMF
http://www.FerrellEngineering.com
RE: Fillet Welds in OMF
RE: Fillet Welds in OMF
http://www.FerrellEngineering.com
RE: Fillet Welds in OMF
In the end it may just be semantics. When I have calced a double-sided fillet weld the weld size was large enough that it seemed to make sense to just use the complete joint penetration weld.
RE: Fillet Welds in OMF
Using R = 3, and avoiding AISC 341, is always an option. Depending on the number of seismic connections, the cost of larger foundations may be reasonable. These details, even OMF, have significant fabrication and erection costs.
http://www.FerrellEngineering.com
RE: Fillet Welds in OMF
jd:you have a good point, the prlim beam size is W14x30 (it a small pipe rack) and per section 11.2a the required flange tension force is 105k +/- which would result in a 5/8" fillet weld which is greater than the beam flange thickness.
I may look at a few more beam sizes before I completely ditch the fillet weld option. A large fillet weld in the shop may be worth it if it results in not having to use demand critical welds and the extra fab costs of the weld access holes per 350, etc.. .
RE: Fillet Welds in OMF
To confirm my thoughts, I e-mailed the AISC Steel Solutions center to ask for their interpretation of the code section. My question/response is as follows:
Question: I have a couple of questions regarding the welding requirements of an OMF. Section 11.2a (3) states that double-sided fillet welds need to be sized for 1.1RyFyAg of the connected part. Is this statement intended to imply that a double-sided fillet weld may be used in the connection between a moment frame beam and a moment frame column in lieu of the complete joint penetration connection that is more typical? Or is this statement only intended for fillet welds in continuity plates, cover plates, etc.
Answer: Fillet welds are allowed at the beam-to-column flange connections.
RE: Fillet Welds in OMF
I have looked at this alittle more also and I am unable to see how a fillet weld can be sized for the 1.1RyFyAg however. I think I am missing something.
I am assuming the Ag = the flange area of the beam (delivering the tension to the column). Is this correct?
Using ASD with Ag = Area of the beam flange,
T =(1.1/1.5)RyFyAg = with Ry = 1.1 and 50 ksi = 40.3ksi*Ag = 40.3ksi*(bf*tf)
For sizing a weld (360 page 8-8) Rn/FS = 0.928D*L(length weld)
L = say 2xbf (will always be less due to k1)
setting T = Rn/FS
40.3*(bf*tf) = 0.928*D*2bf
21.7*tf = D (in 1/16 inch)
1.35*t.f = D (in 1 inch)
Which means the required double sided fillet weld size is always 133% +/- of the flange thickness. I do not see how this could work.
RE: Fillet Welds in OMF
The Steel Solutions response may be an impractical suggestion.
http://www.FerrellEngineering.com
RE: Fillet Welds in OMF
While others may disagree with me, I think that even if the weld was thicker than the flange thickness that it would be "ok". Per AISC 360 you are supposed to check the weld strength based on the lower of the base metal strength or the weld strength. The code is essentially making you design on a capacity based approach to develop the full-strength of the base metal. Therefore, your weld strength can be based solely on the weld thickness. I know a lot of engineers don't like to size fillet welds larger than the base metal, but I don't think its technically not allowed.
All of this essentially points to the fact that maybe a double-sided fillet weld is not the best option, although it is technically allowed.
RE: Fillet Welds in OMF