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Re: Vertical component of EQ in UBC97 and IBC2000

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On Nov 9, 2004, at 11:56 AM, Harold Sprague wrote:

I will share what I can.
I'm grateful.
The buckling occurred along the complete circumference at the base of the tank.
In the tank business, this isn't a hoop stress failure, strictly speaking, but that's only a quibble. According to a paper from Structural Engineering International, elephant foot buckling results from high axial stress, attributable to loading from what they call convective motion of the contained fluid. You're right about a resonant sloshing movement, but I think impulsive load will cause liquid waves. There's also some amplification of the ground acceleration. My guess is that these loads result from horizontal ground acceleration. Vertical seismic motions would certainly aggravate matters though. i hasten to add that I'm only parroting from the paper which cites the EERI Reconnaissance report and some others which discuss tank damage.

What failed on the bridge cranes? Girders, end trucks, connections?
Nothing until it hit the ground.
That'll do it every time… The 25-foot-drop-onto-the-shop-floor limit state is rough on them. I confess I figured this was the failure mode, since I'd seen some other reports on the topic. It's pretty unlikely that a crane is carrying its maximum load at the most critical configuration at the time an earthquake hits; the unloaded structure is plenty strong enough, as a result. And if the trolley isn't loaded it's most likely to get tossed off the rails when things start shaking.

I appreciate the time you took to respond.

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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