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RE: storage racks with partially restrained moment connections - wind frame analysis in high seismic zones

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I must be getting senile if I can't express that I realize that it's not a
drift limit. It's something far worse.

It's a requirement that the installation satisfy this separation (H/20 is
what you gave me). That means a rack must be placed more than 5% of its
height from a structure to ensure separation. In a typical 20" tall rack,
this is 12" from any other structure or element. In a 40' rack (not at all
untypical) this is 24". Racks do not move this much in an earthquake, and
therefore the separation is excessive. Indeed, the spectral displacement of
the earth for the UBC earthquake on aluvium is only around 6". 12" is
probably overkill. 24" is ridiculous. It also fails to recognize the common
fact that most racks have different drifts in their principal directions.

The problem is that I don't know of a single rack installation among the
thousands in my experience which would satisfy the requirement, including
my own where I have often been criticized for "wasting valuable space".
Further, I know of no other colleague insisting upon this extreme

Conclusion: This regulation neither reflects theoretical reality, nor
actual practice.

However, I find out (in a list server of all places) that it is formal
NEHERP regulation. I have no idea how this came to be. Never got a formal
notice of code change, public announcement, etc. It certainly neither
reflects what's out there, nor what the earthquake will do. Then I'm told
that it comes from a single person associated with the RMI?  It's a classic
case of code being promulgated without any public comment, and exactly what
some other threads have been about.

Boy, talk about the old smoke filled rooms. They had nothing on our modern
smoke free conference tables. I have a high regard for NEHERP and the
persons involved, but I never knew NEHERP was this easy to manipulate.


Peter Higgins

Message text written by INTERNET:seaint(--nospam--at)


Peter Higgins


I have repeated it several times,  THIS IS NOT A DRIFT LIMIT!!!

Please read the NEHRP and the RMI.
It is what the movement the installation is to accommodate.

Harold O. Sprague<