Beam to Column Joints in OMF
Beam to Column Joints in OMF
(OP)
According to 2002 AISC Seismic Provisions, Sec. 11.2(1) FR moment connections need to be designed for the flexural strength of the beam defined as 1.1RyMp. I am using a WUF-W connection (FEMA 350 Sec 3.5.2), which has the beam flanges welded directly to the column flanges. For the CJP groove weld at the top and bottom flange, the tension capacity is 0.9FyA. How can this requirement be satisfied when the capacity of the weld is equal to the flange tension capacity but the required strength is the beam capacity increased by 1.1Ry? For a W18x 50 beam, 1.1RyMp = 1.1*1.1*50ksi*101in3 = 6110 in-k which results in a flange force of 6110/18in = 340k. The capacity of a CJP groove weld would be 0.9FyA = 0.9*50ksi*7.5in*0.57in = 192k. Please explain where I am going wrong.






RE: Beam to Column Joints in OMF
Do the same calculation with a heavier W18 - say a W18x175
1.1RyMp = 6413 in-k
Flange force = 6413 / (20.04-1.59) = 347.6 kips
Weld - .9 x 50 x 11.375 x 1.59 = 813 kips
So what you have is a too-deep beam for your situation. Otherwise you will have to build-out the end connection similar to the examples shown in the AISC Seismic Commentary (See Figure C-11.1 in the 1997 yellow book) where a haunch, stiffening rib or cover plate is used.
RE: Beam to Column Joints in OMF
1.1RyMp = 1.1RyFyZ = 1.1*1.1*50*368 = 24079in-k (not 6413)
Flange Force = 1305k > Weld capacity = 813k
Is that right?
RE: Beam to Column Joints in OMF
1.1RyMp = 1305 flange force - you are right - now I'm flumoxed.
RE: Beam to Column Joints in OMF
I believe that post-Northridge design requirements try to force the plastic hinge away from the column flange by forcing you to reinforce a short portion of the beam at the end (per my last paragraph above). This then would allow you to satisfy the 1.1RyMp = Mu limit.
But the 1.1RyMp limit also includes the statement "or the maximum moment that can be delivered by the system, whichever is less." Many times you floor or roof diaphragm cannot transfer enough lateral shear to develop the beam to 1.1RyMp so you can use the smaller value if this is the case.
Because of this insistence that the hinge occur in the beam and not the connection, some proprietary connections have been developed (SidePlate connection and the RBS -reduced beam section or dog-bone) to reduce the beam's 1.1RyMp and then not require a built-up connection, which is more expensive.
RE: Beam to Column Joints in OMF
RE: Beam to Column Joints in OMF
Note that the FEMA 350 OMF is the same as the AISC 2002 Seismic Provisions IMF. Only the name has changed. So just call the system an Intermediate Moment Frame and avoid the whole issue.
RE: Beam to Column Joints in OMF
EBF - you can use those connections IF the maximum force that can be dragged into the system is less than 1.1RyMp (under the OMF - without considering Taro's comment).
RE: Beam to Column Joints in OMF
If I understand correctly, according to the 2002 AISC Seismic Provisions, the OMF connections don't have to be prequalified, they just have to meet the 1.1RyMp strength requirements. And the IMF is basically an OMF per FEMA 350 with a prequalified connection, right?
RE: Beam to Column Joints in OMF
RE: Beam to Column Joints in OMF
RE: Beam to Column Joints in OMF
RE: Beam to Column Joints in OMF
Now my problem is everytime i start to compute still my basic problems is the assumption of loads. it all started when i used STAAD Pro. because the results is always higher than what my own computation. Is it my loads that im using is not enough and far enough to what STAAD standards have?
RE: Beam to Column Joints in OMF