Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

RE: History of conventional wood framing- update

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Annotated following:

Bruce Shephard
Principal Consultant (Seismic Risk)
Opus International Consultants Ltd
P O Box 12,003
Majestic Centre, 100 Willis Street, WELLINGTON, NEW ZEALAND
E-mail: bruce.shephard(--nospam--at)
Telephone: +64 4 4717597 Bus,
           +64 4 5863652 Res.
Facsimile: +64 4 4711397

> -----Original Message-----
> From: Lynn [mailto:lhoward(--nospam--at)]
> Sent: Monday, 22 February 1999 15:26
> To: seaint(--nospam--at)
> Subject: Re: History of conventional wood framing- update
> Oshin
> I agree with the first part and disagree with the very last part.
> The fact is that unless there are some very unusual circumstances or
> some very specific well known deficiencies present, the low rise wood
> frame structure will not pose a life-safety risk in an earthquake.  We
> only have to look at Northridge to see this.

Ageed.  My models show that if the great New Zealand earthquake [M 7.5
direct hit on Wellinton City] occurs at a time when people are generally at
home in their low rise wood framed house, then about one tenth of the
fatalities occur.  I.E.  60 vs 600 deaths.  This is based on data ex US,
[ACT - 13, HAZUS] and Cambridge University, UK.

> I am at a loss to explain all these supposed "lessons learned" from the
> Northridge earthquake.  As far as our Code being deficient from a
> life-safety prospective, there were only a few "lessons learned".  The
> behavior of the tucked under garage supported on small diameter steel
> columns, steel moment connection problems, and perhaps some problems
> with tilt-up wall to roof connections.
> I observed HUNDREDS of damaged 1960's and earlier, low rise, wood
> framed, plaster and drywall type buildings.  From a Life-safety
> perspective, they ALL did fine.  I know one house slid down a hill, and
> a few others had some problems, but when you consider the MILLIONS of
> older wood framed structures that performed adequately from a life
> safety perspective, I was SHOCKED when the City of LA and now the
> upcoming UBC (to a lessor degree though) made major changes is the
> seismic design requirements for these buildings.  If you pull out the
> 1997 UBC and use it to determine the adequacy of a three story wood and
> plaster structure, it wood fail miserably.  Plaster and gypboard are now
> considered worthless when resisting seismic forces.  Yet, it seems to me
> that these materials seemed to provide basic life safety for their
> occupants.

Plaster and gypboard are considered effective in New Zealand construction.
There are currently good construction practices.  See

Damage ratios at MMIX are less than 10%.

> I know this is an unpopular point of view, and I have wanted to post
> something about this for a long time.  These structures do not do very
> badly at limiting damage either, although I do acknowledge that most of
> these building required a lot or repair.  However, very few actually
> needed to be torn down and replaced.
> So I for one do not buy into the popular notion that drywall and plaster
> cannot be used effectively to provide a basic life-safety level of
> protection to the occupants of low rise wood framed buildings.
> There, I said it.  :)
> Lynn