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Re: EQ resistant Design

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>Simple observation of any three-component accelerogram suffices to prove
>that component maxima do not  happen simultaneously, that means the
>resultant vector describing the seismic motion does not keep its direction
>constant.
I just had a look at two accelerograms (El Centro 1940 and Taft 1952) in
TID-7024, and they certainly aren't affine. Major peaks occur at roughly
the same times, but the ratios of the peaks isn't constant. I bet slip
propagation along a fault line in big quakes provides varying directions
of travel of seismic waves and anisotropy of soil and rock changes the
direction of motion when (say) the NS wave propagation lags EW
propagation. I suspect if earthquakes were point sources the direction
wouldn't change, and it would look like the shock waves you see in
pictures of nuclear explosions.

I'm forced to admit I've never given a lot of thought to how the response
spectra I use or the time histories I'm sometimes forced to use actually
relate to real earthquake motion. Probably it shows.

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


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