Seismic Loads according to the 2005 National Building Code of Canada

[Robbiee]

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

 

[Robbiee]

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

 

[ChadV]

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...

 

[Robbiee]

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.

 

[JoshPlumSE]

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.