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

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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 2000
IBC now appears to require orthogonal effects to be considered for seismic
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