RBS or WUF-W Flange Force
RBS or WUF-W Flange Force
(OP)
Hello everyone,
I have what may be a simple question. I'm looking at designing some moment connections for an Intermediate Moment Frame. I'm between using and RBS or WUF-W connections (I've asked for fabricator input). One thing I've noticed is that the design examples I've found don't check the beam flange's ability to carry the flange force from the design moment. For example on a standard R=3 direct welded moment connections with a bolted shear tab I always verify that the beam flanges will be able to actually carry and transfer the flange forces resulting from the design moment to the column. The RBS example in AISC 341-10 does not consider this failure mode. This may be, in part, since the web of the beam is CJP welded to the column. If a bolted web connection is used in an RBS wouldn't the flanges be required to develop the couple from the "probable maximum moment"? Same question applies to the WUF-W.
Hopefully this is a simple answer and I just am missing something.
Thanks in advance!
I have what may be a simple question. I'm looking at designing some moment connections for an Intermediate Moment Frame. I'm between using and RBS or WUF-W connections (I've asked for fabricator input). One thing I've noticed is that the design examples I've found don't check the beam flange's ability to carry the flange force from the design moment. For example on a standard R=3 direct welded moment connections with a bolted shear tab I always verify that the beam flanges will be able to actually carry and transfer the flange forces resulting from the design moment to the column. The RBS example in AISC 341-10 does not consider this failure mode. This may be, in part, since the web of the beam is CJP welded to the column. If a bolted web connection is used in an RBS wouldn't the flanges be required to develop the couple from the "probable maximum moment"? Same question applies to the WUF-W.
Hopefully this is a simple answer and I just am missing something.
Thanks in advance!






RE: RBS or WUF-W Flange Force
Basically design for applied loads then modify only as required by the explicit prequalifcation requirements of AISC 358.
Thoughts/comments?
RE: RBS or WUF-W Flange Force
RE: RBS or WUF-W Flange Force
RE: RBS or WUF-W Flange Force
I guess I'm saying there are two design processes to satisfy:
1) Design the entire connections for any applied load from analysis. This would include any checks for the flange force resulting from all moments from design loads.
2) Analyze/verify the connection from (1) satisfies all requirements of 358 (which do not include a check of the flange force. At least from what I can see (pgs 9.2-16 through 9.2-19 from AISC 358-10).
RE: RBS or WUF-W Flange Force
You are permitted to use the full Zx of the beam, not just the flanges. The rationale is explained in the link I posted above. If you still can't make it work, you need to adjust the dimensions of the RBS cuts.
Step 1 is unnecessary for the design of the connection (with the exception of panel zone shear). Once you size your frame members, jump straight to the mechanism design outlined in AISC 358.
RE: RBS or WUF-W Flange Force
I agree - the whole point of capacity design is to utilize the full plastic capacity of the section. My issue is if I have to design a connection to develop the full plastic capacity - I can't do that with only welding the flanges.
I think we may actually be agreeing here...? For clarity I'm saying that regardless of the seismic design provisions, my beam and connection have to be able to adequately carry the actual applied loads from analysis (combinations of dead, live, wind, and seismic loads from an equivalent lateral force procedure or other EQ analysis). The capacity design from AISC 358 is in addition to this analysis. I believe you confirmed what I'm saying - once I'm doing the AISC 358 stuff the only "conventional" connection design checks are for the panel zone shear and column flange stiffeners.
RE: RBS or WUF-W Flange Force
Did you read the link I posted above? Or the commentary to AISC 358 5.6?
RE: RBS or WUF-W Flange Force