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Re: 97UBC Seismic

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Jeff,

First some global definitions: UBC Chapter 22 Division I are general steel requirements, Division II are the basic (non-seismic) LRFD requirements, Division III are the basic (non-seismic) ASD requirements, Division IV are the LRFD Seismic provisions, and Division V are the ASD Seismic provisions.  Divisions II and III are referencing the basic AISC manuals.  Division IV (LRFD Seismic) references the outdated 1992 AISC Seismic Provision with extensive modifications and Division V (ASD Seismic) are slightly modified requirements from the 1994 UBC (i.e. not AISC).

As you can see this is a real mess, but in fairness to the authors this was a time of significant change and transition mainly due to the Northridge lessons learned, the SAC investigations (later to become FEMA 350/353), and the introduction of the IBC.

I am not sure what you mean when you say conversion factor and perhaps we have some apples and oranges mixed here.  There are areas where the code is trying keep certain critical items in the elastic range and this is primarily done by multiplying the derived seismic load by omega.  Where the code requires that you check the "strength" of a member, and you are using ASD, you use UBC Section 2213.4.2 for the allowables.

FEMA 350/353 are not codes and as you pointed out they are not reference by the code.  However, a jurisdiction MAY accepted these documents as fulfilling the requirement that moment connections be tested.  You need to be careful here since some building departments will accept all 9 prequalified connections, some will only accept the RBS connection, and there may be some old farts who wont accept any.

As for knee braced connections, this was just recently discussed and on the list and I suggest you go to the SEAINT Archives at:

http://www.seaint.org/mailarchive.asp

Thomas Hunt, S.E.
ABS Consulting




"J+R" <jeffrandi(--nospam--at)adelphia.net>

12/17/2002 10:07 AM
Please respond to seaint

       
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        Subject:        97UBC Seismic




I would appreciate some input on a couple questions regarding a 1-story building in seismic zone 4.

OMF per 97UBC 2213.6 #2:  This sections requires design strength of the connection be 2.8 times design seismic forces.  Section 2213.4.2 does not appear to have the required conversion for this.  The AISC Seismic Provisions have the conversions but this document is not referred to in Ch 22 Division 3 or 5.  What am I missing?
Also, when are the FEMA-350 recommendations typically followed in addition to the applicable building code?


Knee braced frame per 97UBC:  How are knee braced frames classified?  They must be permitted as they are commonly used in pre-engineered buildings.   The only reference that may apply is Section 2213.8.1 which refers to 2213.7 for 'members which resist seismic totally or partially by shear or flexure'.  Are they any other references? (I doubt pre-engineered buildings are designed per SMRF)

Thanks in advance.
Jeff