Tuesday, February 9, 2010

The Death of PGA


Well, I'm into a new experiment this year, where I am getting my BSSA journals electronically. I can download them to my Sony PRS700, and read them on the couch! The lead article is a compilation of peak ground motions to this date. It's a very interesting read, which basically says that peak ground acceleration (PGA) can be extremely high for a teensy earthquake, but that a high PGV needs a larger earthquake.

As well, PGA does not scale with magnitude, but PGV does. I've been saying this for years, but the stubborn old engineers must stick to PGA. This is another nail in their coffin. They say they need the loads that PGA supplies, but earthquake motion is really a forced displacement, not a load, and PGV is fine for this.

If I were in charge of our next nuclear station (Ha!), I would just use PGV. Surely these old guys must be dead by now?


Anonymous said...

We engineers need that "A" in F=MA don't you know. How would we equate a force to velocity!

Harold Asmis said...

An earthquake is a forced strain, scaled to PGV. Old engineers simulate it as a free following force, scaled to PGA. This is wrong.

Smart engineers, who design structures with energy absorbing elements know this, but keep it to themselves. It's a pity that the nuclear industry is packed with old engineers.