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Seismic Loads according to the 2005 National Building Code of Canada

Seismic Loads according to the 2005 National Building Code of Canada

Seismic Loads according to the 2005 National Building Code of Canada

(OP)
The minimum Base shear is calculated as:
V=S(Ta). Mv. Ie. W/ (Rd.Ro),
S(Ta) and Mv are a function of the Fundamental Lateral Period, which intern is a function of the height of the building, or the number of stories.
My question is: How is the base shear different in different directions?
Thanks  
 

RE: Seismic Loads according to the 2005 National Building Code of Canada

(OP)
I guess I should've stated that the building has the same type of lateral resisting system in both directions, shear walls for example.  

RE: Seismic Loads according to the 2005 National Building Code of Canada

I suppose in that case they wouldn't be different, as long as you're using the approximations for fundamental period rather than a more detailed model which would give you different periods in the two directions if the building isn't symmetric in plan.

I think I might not be understanding your question though...

RE: Seismic Loads according to the 2005 National Building Code of Canada

(OP)
Chadv,
Thanks for your answer. I am doing a review for a concrete building, in which shear walls are used as SFRS. The drawings show different (Ta) for the two directions and hence two different base shear values. I think the base shear in the current code is not a function of the direction if same type of SFRS is used.
 

RE: Seismic Loads according to the 2005 National Building Code of Canada

I haven't looked at the NBCC in a while, but I didn't think that you were ever REQUIRED to use their simplified periods based on building height.  

If you've got an 80 foot long shear wall in one direction and a 20 ft long shear wall in the other direction, then it makes sense that the period would be different for the two directions.... regardless of what the "simplified" formulas say.  
 

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