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RE: 2000 IBC seismic design category D - orthogonal effect requi rement

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The 1994 UBC section 1628.1 states "Structures shall be designed for
seismic forces coming from any horizontal direction."  This is a nice
simple declaritive statement that applies to all structures.

The orthogonal effects provision is simply a way to account for this
without requiring analyses at multiple directions.

 The excemptions are an attempt to list common situations where for one
reason or another the code authors felt that this effect would be small
enough to ignore.  If this  effec t is significant for your structure then
it should be adddressed.

Mark Gilligan

>Do you need to consider orthogonal effects now when calculating story
and building separations with the new 2000 IBC?  This is pertinent to a 10
story building that I am reviewing under the IBC.

> -----Original Message-----
> From: Haan, Scott M. [SMTP:HaanSM(--nospam--at)]
> Sent: Monday, March 12, 2001 5:09 PM
> To:   Seaint list (E-mail); Se-Practice List (E-mail)
> Subject:      FYI: 2000 IBC seismic design category D - orthogonal effect
> requi rement
> Your following message has been delivered to the list
>   seaint(--nospam--at) at 18:19:51 on 12 Mar 2001.
> 1997 UBC 1633.1 required orthogonal effects to be considered in seismic
> design for columns at intersecting LFRS grids when Pu_seismic>.2*f*Pn.
> The
> 20% column capacity rule appears to be gone in the 2000 IBC.  The The
> IBC now appears to require orthogonal effects to be considered for
> design category D for all conditions.
> For seismic design category D, IBC 1620.3.5 indicates that considering
> each
> direction independently per IBC 1620.1.10 is not considered acceptable.
> Also for design category D, IBC 1620.3.5 indicates for any structure that
> considering SSRS or 1*EQx+.3*EQy or 1*EQy+.3*EQx per 1620.3.5 is
> acceptable.
> In English: orthogonal effects need to be considered in design category D
> for columns, braces and beams.
> Scott M Haan  P.E.
> Plan Review Engineer
> Building Safety Division, 
> Development Services Department,
> Municipality of Anchorage
> phone: 907-343-8183   fax: 907-249-7399
> mailto:haansm(--nospam--at)
> <