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Drift limitation

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from Dennis:

"Martin, if you can't comment who will and who should or are we simply to waste
time hunting for the information or drawing our own interpretation."

Actually, I thought the discussion yesterday pretty well covered the basics.

The topic of whether 30-7 should be excepted came up at the last seismology
meeting, and I was very much surprised when I heard Bob Bachman agreeing with
John Hooper that there had been talk about allowing the exception at the ICBO
convention.  However, Charlie Kircher, who chairs the ground motion committee,
recalled that the concerns of Hall & Heaton about velocity pulses were also
being reviewed by the committee at about the same time as the IBCO convention,
and that the perservation of the 30-7 equation was considered at that time as a
measure of protection for tall buildings.

I really can't tell you exacty what agreements may or may not have been made - I
was not there, and I have heard some conflicting recollections myself.

The fact is that the requirements for drift of tall buildings have already
relaxed in the 97 UBC even when Eqn 30-7 is considered because in the 94 and all
earlier codes the force used to check for drift was greater.  I personally do
not think that it is appropriate in zone 4 to push the envelope further and
remove the 30-7 limitation. Whether it had any different meaning or purpose in
earlier codes is irrelevant, it is it's relevance today that matters.