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Re: Does AISC Seismic Section 11.2a apply to MBMA ordinary moment connections?

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Title: Does AISC Seismic Section 11.2a apply to MBMA ordinary moment connections?
Scott,
 
You have raised an excellent and very timely question -
 
I suspect a number of us are waiting for a clear response....
 
There are special divisions in the MBS industry that deal with heavy/industrial structures, and these entities can and will perform the design and manufacture to the AISC Seismic Provisions-2002.  But their systems generally bear little resemblemence to the MBS systems we are accustomed to. 
 
The question is, what about everybody else competing for the remaining 98% of the MBS market?. 
 
Mark D. Anderson
Anchorage
 
 
 
----- Original Message -----
Sent: Friday, March 26, 2004 1:33 PM
Subject: Does AISC Seismic Section 11.2a apply to MBMA ordinary moment connections?

Some one has indicated to me that the metal building industry is not designing ordinary moment connections per the exact wording in AISC Seismic section 11.2a.  I have not checked if this has been discussed on the list before.

American Institute of Steel Construction [AISC] AISC Seismic Provisions Section 11.2a indicates that fully restrained ordinary moment connections need to be designed for a flexural strength Mu that is at least equal to 1.1*Ry*Mp of the beam or the maximum force that can be delivered to the connection by the system or need to demonstrate an inelastic rotation of at least .01 radians per AISC Seismic Appendix S and Section 9.2a.   The special load combinations incorporating the over strength factor are meant to approximate the maximum force that can be delivered to an element by the system. 

It is come to my attention that it is the metal building industry standard practice to design ordinary moment connections for the special load combinations and not the options specifically written in the code: tested or 1.1*Ry*Mp or maximum load that can be delivered to the system.  The Metal Building Manufacturer?s Association [MBMA] in conjunction with the AISC are in the process of drafting the ?MBMA Seismic Design Guide for Metal Buildings" which will allow ordinary moment connections to be designed for the special load combinations.

Are other jurisdictions allowing special load combinations to design ordinary moment connections as an approximation of the maximum load that can be delivered to the connection by the system?

Why aren't the AISC Seismic Provisions written to allow the special load combinations specifically for ordinary moment connections? 

Are the AISC Seismic Provisions going to be modified to specifically allow this method of determining the internal forces for designing ordinary moment connections?


Scott M. Haan P.E.
Chief of Building Inspections
Municipality of Anchorage
Development Services  Department