Re: Re: Fw: Seismic Designs

>Many seismic failures were the result of seismic anchor motion at
>equipments or at the supporting structures where the designer had
>originally assumed rigid.

All such failures are ultimately due to motion of the anchor points. During an earthquake the ground oscillates carrying the supports with it. The inertia of the piping itself and its elasticity cause deformation because the inertia piping can't follow the support movements and lags behind. Because the ground motion is oscillatory there is dynamic amplification depending on the frequency content of the ground movement. It's this dynamic amplification which causes the damage. The actual ground acceleration is rarely above 0.5 g in the US (I think the New Madrid quakes was estimated to be somewhere around 1g) with an amplification of 10-20 depending on the frequency of the system. There is no dynamic amplification at the supports--they have substantially the same motion as the ground.

>I have not seen seismic failure purely because of the inertial loading of the
pipe.
Once again, all earthquake failures result from inertia loading. The dynamic response of the structure--its inertia--amplifies the oscillatory ground motion.

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