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RE: Ordinary moment connections - pre-engineered metal buildings

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One building manufacturer told me one way they can get around the special
moment connections: fully brace the roof and end walls for lateral forces,
i.e. make the lateral force resisting system to be a concentrically braced
frame. Then they use Section 14.5 of the AISC Seismic Provisions to permit
design using omega forces (for low rise buildings). 

They still use the ordinary moment frame for vertical loads but do not use
the moment frame to resist lateral loads. 

William C. Sherman, PE
(Bill Sherman)
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com


-----Original Message-----
From: Haan, Scott M. [mailto:HaanSM(--nospam--at)ci.anchorage.ak.us] 
Sent: Monday, April 05, 2004 3:11 PM
To: seaint(--nospam--at)seaint.org
Subject: Ordinary moment connections - pre-engineered metal buildings


Someone 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 
Mission Statement:  Guide safe construction and responsible development for
the community. 

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