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Re: AISC Seismic Provisions for SCBFs

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In a message dated 4/15/99 2:49:06 PM EST, John.A.Connor(--nospam--at)nwk02.usace.army.mil 
writes:

<< For example, for most of the Midwest or areas of low seismic forces, wind
 forces would generally "control" over the seismic forces.  Since my wind
 forces control, my members are designed for elastic responses.  These
 members wouldn't be able to reach deformation levels since my seismic forces
 are so low.  Since I expect the members to remain elastic, I believe these
 members would be considered "force-controlled" members rather than
 "deformation-controlled" members.  
  >>

The seismic forces are not necessarily low in the Midwest, remember that some 
of the largest earthquakes to occur in the United States occurred in the 
Midwest and East Coast in the early 1800s.  What is low, is the expected 
reoccurrence interval of these larger earthquakes.  Should one of these 
larger earthquakes occur in the Midwest during the lifetime of this 
particular building, you would have to depend upon the ductility of the 
bracing system, which is accomplished in some cases by code prescriptive 
requirements such as occurs in member size selection and connection design.

As far as wind governing design, the UBC building code still requires that 
detailing requirements and limitations satisfy seismic design requirements 
(1994 UBC, 1624.2 Seismic and Wind).

Michael Cochran