Friday, March 3, 2017

Base Isolation as useless as I always said it was


I remember when base isolation was a big thing.  I said "Blah, you don't know the physics.', or something like that.  BI was another corruption from 'Shake Table Garbage'.  At that time, the path to engineering glory was to build a bigger shake table, perhaps it still is.

Base isolation and crapping around with shake tables only ever gave you a factor of two, in terms of PGV.  Locating on soft soil was over a factor of 10.  All of this destruction comes from a devotion to peak acceleration rather than PGV.  I would have liked to see the velocities when this thing jumped the rails.

Believe it or not, no engineer learns from this because it didn't happen in California.  Also, you will have to take the shake tables out of their cold dead hands.  The experience in Chile didn't change things, and this won't either.  Look for more spectacular failures of engineered structures when the PGV exceeds 40 cm/s.

No structure should lose it's functionality with 20-40 cm/s PGV.  I think structures should go up to 80 cm/s, but people will regard this as a building code success, since it didn't pancake.  Blah.

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