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RE: OMF connections -special load combinations used to approximate maximum force to system?

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Charlie:

Another similar issue is whether a panel zone can determine the maximum force that can be delivered to an ordinary moment frame connection by the system.  Another pre-engineered metal building manufacturer is arguing that the panel zone strength can be used to determine the maximum force that can be delivered to an ordinary moment frame connection by the system.

It has been our interpretation that a panel zone is part of the connection and cannot be used to determine the maximum force that is delivered to the system.  Should panel zones of ordinary moment frames be designed for the lesser of the 1.1*Ry*Mp or the maximum force that can be delivered to the system?  Can panel zones be used to determine the maximum force that can be delivered to an ordinary moment frame connection by the system?
 
Thanks.
Scott Haan
-----Original Message-----
From: Carter, Charlie [mailto:carter(--nospam--at)aisc.org]
Sent: Wednesday, July 07, 2004 6:21 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: OMF connections -special load combinations used to approximate maximum force to system?

Scott,

 

I took some time off and am still catching up. I will have a response for you soon.

 

Charlie

 


From: Haan, Scott M. [mailto:HaanSM(--nospam--at)ci.anchorage.ak.us]
Sent: Wednesday, July 07, 2004 9:13 AM
To: seaint(--nospam--at)seaint.org
Subject: OMF connections -special load combinations used to approximate maximum force to system?

 

Everyone:

Dead horse whipping.  I know there is someone from AISC or MBMA reading this.  Locally, there has been a metal building manufacturer that has been designing their ordinary moment connections for the seismic special load combinations which include OMEGAo.  The manufacturer's contention has been that it was allowed in the 1997 UBC and that the AISC Seismic Provisions on ordinary moment frame connections are vague about whether the maximum force that can be delivered to ordinary moment frame connections can be approximated by the special load combinations including OMEGAo.

I pointed out to the manufacturer that the 2000 IBC Table 1617.6 "Design coefficients and factors…"  item 3D "Ordinary steel moment frames" already has a special exception that allows ordinary moment frames with end plate moment connections in seismic design category D.  I asked why doesn't it say "end plate moment connections designed for the special load combinations"?

The 1997 AISC Seismic Provisions Section 14.3a say that ordinary concentrically braced frame connections need to be designed for the least of: the maximum force that can be delivered to the system, the special load combinations or the Ry*Ag*Fy.   Section 13.3a says that special concentrically braced frame connections need to be designed for the least of: Ry*Ag*Fy or the maximum load that can be delivered to the system.  I asked a representative from the premanufactured metal building manufacturer whether this was ambiguous and meant that special concentrically braced frame connections can be designed for the special load combinations because these approximate the maximum force that can be delivered to the system?

Section 11.2a similarly indicates that ordinary moment frames can be designed for the lesser of the maximum force that can be delivered to the system or 1.1*Ry*Mp.   I received the answer that the AISC Seismic Provisions are ambiguous on whether the special load combinations can be used to approximate the maximum force that is delivered to the system. 

Can the special load combinations be used to approximate the maximum force delivered to the system for ordinary moment connections?  For specially concentrically braced frames?  Are there any code changes in the works clarifying the issue for pre-engineered metal buildings?

Thanks.

Scott M. Haan P.E.
Deputy Building Official