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Re: EQ resistant Design

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Earthquakes initiate several types of elastic seismic waves from the
hypocenter.  Each wave has its own characteristics.

The P-Wave are the fastest and act like a sound wave pushing and pulling
through the rock.  Although the general direction is away from the
hypocenter, it acts much like a slinky, felt as a sinusoidal horizontal
motion by a fixed structure as the waves pass.  More important are the
damaging S-Waves which acts like a sound wave and moves at right angles to
the direction of travel.  This is also felt as a sinusoidal horizontal
motion by a fixed structure.  The other waves (Love and Rayleigh) have a
lesser impact on fixed structures on typical frequency ranges.

Of course if you are close to or above the earthquake hypocenter, the fixed
structure will also feel a vertical component of the waves causing
sinusoidal vertical motion.

Rick Drake, SE
Fluor Daniel, Aliso Viejo, CA

*********************




                    Christopher
                    Wright               To:     "SEAOC Newsletter" <seaint(--nospam--at)seaint.org>
                    <chrisw@skypoin
                    t.com>               cc:
                    03/20/02 03:05
                    PM                   Subject:     Re: EQ resistant Design.
                    Please respond
                    to seaint                                                                                    .






> I think that what differentiates the seismic load  from other usual (more
>or less static) loads, is the dynamic character of its continuously
changing
direction.
My understanding is that the horizontal motion is pretty much wave motion
in the direction of slip along a fault, although reflections and
diffraction change that. The motion is oscillatory so it changes in
magnitude but not in direction. I don't see how surface wave motion can
change direction.

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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