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RE: 5/8" dia. a.b.

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In the handout booklet prepared by ICBO when they were giving seminars on
the 97 UBC, it said that the detailing was beefed up due to poor performance
of hold-downs observed after the Northridge earthquake, however the nature
of the problem as it relates to bolt size was not clear. The commentary in
the 99 SEAOC Blue Book has an Appendix written after Northridge which says a
number of problems were observed related to poor construction practice, such
as bolts that were bent or misplaced during construction, then tried to
straighten out when tension was applied. Maybe the intent of this section is
require bolts which are less susceptible to poor installation.

-----Original Message-----
From: Mark D. Baker [mailto:shake4bake(--nospam--at)]
Sent: Tuesday, September 19, 2000 10:04 AM
To: seaint(--nospam--at)
Subject: 5/8" dia. a.b.

Does anyone know why sill bolting in residential construction in zones 3 & 4
is now required to be 5/8" dia. anchor bolts instead of 1/2" dia.?
For some time now, I beleived 5/8" dia. were required only if utilizing the
prescriptive measures for construction. This belief was due to my attending
a seminar on the 97 UBC at which the speaker said "Section 1806.6 only
applies to conventional construction, in a designed structure 1/2" dia. a.b.
is o.k." I even wrote down this quote in my code book during the seminar.
I have not yet run into a plan checker who buys into this statement.
Anyone have some insight to this issue?

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