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Re: THAT SEISMIC STUFF NEED NOT BE SO PAINFUL

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On Jan 12, 2005, at 10:30 PM, ASC wrote:

Unfortunately, when you use SAP type FEA, there is not
much else you can do having discrete dampers in the system.
I don't think he actually wants discrete dampers. My guess is that he's looking for the effect of the damping treatment on the overall structure damping ratio. That's not an easy problem, because ordinary FEA codes consider only viscous damping, and real structures don't behave that way. Real world damping depends more on stress level and friction than anything else, and the damping ratios we commonly use are really just artifices that mimic the actual frictional energy dissipation.

Damping treatments are pretty tricky, since you need to place them just right or they don't strain enough to be effective. Harris and Crede (_Shock and Vibration Handbook_) covers this is some detail. Probably a good idea to read through it before starting anything like this.

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


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