From: Allen Adams <aadams(--nospam--at)ramint.com>
Date: Fri, 09 Feb 2001 11:33:01 -0800
Regarding the issue of whether or not Eq (30-7) can be disregarded in the
calculation of drift, I have been corresponding with Gerald B. Neville at
ICBO. His position there is Senior Staff Engineer, Education Services. He
was very helpful. It turns out to be rather complicated, and explains why
there was conflicting information out there, including the message that I
posted last Monday. It appears that as formally voted on and adopted, the
UBC should have indicated that Eq (30-7) can be disregarded (so, it would
seem, that it is "legal" to do so). However, as is explained in the
Seismology Committee's position paper, there are reasons (apparently not
considered at the time) for including the Equation. The position paper can
be found at:
Click on the link: "SEAOC has released a position paper on the the 1997 UBC
Equation 30-7 and Drift".
Gerald Neville indicated that ICBO has now indicated that they will post an
errata saying that both Equation (30-6) and (30-7) can be ignored in the
drift calculations, since this is what was legally and formally adopted,
even though it may not be the technically correct thing to do. So this is
an issue where it may be technically legal to disregard it, but technically
incorrect to do so.
I have included Mr. Neville's email, below.
"It's a long story with an unfortunate (or fortunate . . . depending on
ones viewpoint) ending. After concluding that Eq (30-7) should not be
exempt from the drift calculations, based on a further review by SEAOC,
a structural engineer from the Seattle area phoned ICBO to challenge
the ruling . . . indicating that he had recollections that . . . at the
final public hearings on adoption of the 1997 UBC revisions . . . SEAOC
motioned to exempt both Eqs (30-6) and (30-7) from the drift calculations
. . . which was accepted by the assembly! Our review of the actions taken
at the hearings verified the motion and assembly acceptance. Therefore,
in accordance with the legal adoption process, both Eq (30-6) and (30-7)
are exempt from the drift calculations . . . and we have submitted an
errata so stating. As you may know, there is no legal process in place
to revise the 1997 UBC . . . right after publication of the 1997 edition,
ICBO ceased all revisions to the UBC . . . all further actions were to be
directed to the IBC.
"The unfortunate aspect of this action is that it is probably "technically"
incorrect . . . the 1999 edition of the SEAOC "Bluebook" does not exempt
Eq (30-7) from drift calculations . . . and interestingly . . . the 2000
does not exempt either Eq (30-6) or (30-7) . . . they both apply for drift
calculations! So there you are . . . in accordance with the 1997 UBC . . .
both (30-6) and (30-7) are legally exempted . . . even though it may not be
I appreciated his responding to my inquiries. He was very helpful. So this
is an issue that will require some Engineering judgement. Technically,
legally, you can disregard it, but a significant part of the Engineering
community is saying that you should not.
Allen Adams, S.E.