Collectors and Drag on light wood framing structure 3

[LGARG]

Hi, i wanted to know if i have to use the omega Factor(2.8)(UBC 97) when i´m calculating a drag or a colector in a light wood framing structure with a moment frames in some lines

 

[NerdSE]

Technically, yes CBC1633.2.6 offers an exception for structures or portions thereof, braced entirely by light frame wood shearwalls... you may ignore the overstrength factor. I would interpret that to require Omega on any shear line with a steel moment Frame but not the rest of the structure.

Don't forget, when you calculate Omega it is strength level, then you can take a 1.7 stress increase for working stress AND you can take the 1.33 duration factor for wood elements.

 

[skier1578]

Thank you NerdSE - We have battled many plan checkers over the reductions allowed. We typically increase required forces by (omega*1.4/1.7/1.33). I am just happy to see someone else does that as well.

 

[LGARG]

Thanks guys, we ussually use the increase factor (1.7*ASD = Strenght design). Do you know what are the story drift limts for wind on the IBC 2006?. i know in the UBC 97 you have to calculate the story drift with Strengh level load combinations, but the IBC is not so clear about that specially regarding wind forces.

 

[OldPaperMaker]

The 2006 IBC basically sez: go buy ASCE7-05 for lateral load design. I believe that the only wind load drift calculations required are to insure that the deflection of the flexible diaphgram is compatiable with the shearwall deflections.
The seismic drift determination process is outlined in section 12.8.6. The Drift & Deformation limits, etc are identified in section 12.12 and the allowable story drifts in table 12.12-1.

 

[LGARG]

Thanks a lot Guys!

Lgrossi
AMP CONSULTING