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Re: Effective first mode weight??

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>"the effective
>first mode weight, which would be on the order of 0.7W" (under "Dynamic
>Response Modification"). What is the basis for this statement?
If the Blue Book is using the term properly (actually it should be 
effective mass) the difference between the effective and actual masses 
reflects the difference between a simple SDOF system with all the mass 
moving at the same speed, and a distributed system where the movement 
varies from zero at ground level to a maximum at the top. It's an 
artifice which allows the balance between kinetic and potential energy to 
be drawn correctly using a more accurate distribution of inertial forces. 
The 0.7 factor applies to a cantilever with a more or less uniform mass 
distribution, and would be higher for a structure like a water tower 
where most of the mass is at the free end, and lower for a structure 
where most of the mass is near the ground. 

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