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Re: EQ resistant Design

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>Yes.  Under most codes in the US, you analyze the building separately in
>each orthagonal direction.
> you are infact achieving a building that has a lateral
>system that is capable of 100% in one direction AND 100% in the other
>direction at the same time
This sounds like a contradiction. How does assessing each load separately
prove that the structure can take both loads simultaneously?

>As you state, the result is that you are in
>effect designing the building for about 142% of the seismic loading if it
>were applied at a 45 degree angle to the primary orthogonal directions.
This would be the equivalent of a simultaneous application of 100% of the
load in one direction (the 'primary' direction, say) and simultaneous
application of the load applied normal to the primary direction.

I'm trying to make an association with nuke plant seismic analysis, where
we'll typically apply horizontal response spectra simultaneously in
orthogonal directions (or have separate EW and NS spectra) and combine
the directional responses on a RSS basis. I'd always assumed that the
horizontal ground motion is pretty much unidirectional but that EW and NS
spectra are found by resolving the ground motion along site EW and NS
directions for convenience in application.

That leads me to believe that building seismic analysis should  be done
applying the given seismic lateral load or acceleration in a 'worst case'
orientation found by iteration or by applying the load is the building's
'weak direction.'

Christopher Wright P.E.    |"They couldn't hit an elephant from
chrisw(--nospam--at)        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)

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