Need a book? Engineering books recommendations...

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

RE: 97 Code is a Life Safety Standard

[Subject Prev][Subject Next][Thread Prev][Thread Next]
At 08:51 AM 9/24/99 -0800, you wrote in reply to Lynn Howard:
>I question why the code writers thought that the seismic provisions
required a purpose but Division I, General Design Requirements, Division II,
Snow Loads, and Division III, Wind Design do not require a purpose. I prefer
the wording of Section 101.2 Purpose. It says it all and is applicable to
the entire UBC.
>
>James Allen, P.E.

-----------------------------
Of many possible reasons for a purpose statement specific to seismic, let me
offer two, and then relate each to present disputes:

[1] In the beginning, before very much had been "begat" by SEAOC et al and
their predecessors, seismic-resistant construction requirements were a hard
sell. They were not traditional, and there was widespread disbelief that a
damaging earthquake would actually happen in the time frame of interest, in
any location anywhere. Every animal accepts and understands gravity, wind,
and rain, but few humans intuitively or willingly accept earthquakes as
something real to provide for in advance.

To make possible ANY seismic code provisions being enacted, they had to be
done with a light touch. Their performance objectives had to be curtailed to
what was politically persuasive and thus enactable. I surmise that the
purpose statements tailored to seismic were primarily to aid the cause of
gaining acceptance of early day seismic provisions, and secondarily to be
informative around the profession and to other interested parties as to what
was intended, and what was not, because the purposes really did differ from
customary code objectives.

An exception that does not disprove this theory is the California state
legislative enactment, effective within 30 days of the 1933 Long Beach
earthquake, that placed public school buildings uniquely under a special and
stringent seismic code that also bore a statement of purpose, this time well
in excess of regular code purposes, and with powerful enforcement means
included. It was the specter of little children crushed under the piles of
brick that temporarily overcame antipathy toward seismic code proposals. Had
the biennially part-time legislature not been in session at the time of the
earthquake, and temporarily in shock, the Field Act may well have not been
enactable. (In recent years it has been in danger of repeal.)

[2] A second reason for a purpose statement is to guide deliberations that
are to flesh out and make specific the general objectives. The late C.
Northcote Parkinson, in his humorous but astute "Parkinson's Law" writings,
notes that the most common failing in deliberative undertakings such as
codewriting is not misinterpretation of the facts, but in not deciding at
the outset what the "aims" truly are; not getting straight what they are
trying to do. One discounts Parkinson's laws foolishly.  

I saw for myself in amazement the muddle that results when aims aren't clear
and kept to. It was at the two-day, September 1984, Oakland meeting of SEAOC
Seismology Committee, then in the throes of the big 1982-87 Blue
Book/seismic code rewrite that came out in the 1988 UBC. I was there as a
first-timer proxy from Central Section. It became evident to me during a
lengthy discussion of the meaning of the proposed Rw factor (successor to
the traditional K factor) that the committee had never resolved what level
of building performance was wanted according to the intensity of earthquake.
The discussion wasn't on any track; it was a lot of mental milling around.
It seemed no focus could occur without settling on damage resistance
objectives, which I humbly pointed out. 

The Committee immediately and without further debate agreed to continue the
criteria set forth in the original 1960 Blue Book Commentary and repeated in
the ATC-3 introduction. This criteria accepts major damage in severe
earthquakes, seeking only to preserve life safety and to prevent collapse of
structural framework and essential components. Then the Rw meanings were
easily resolved.

But that "aims" accord seems not to have been kept in mind later on, and
certainly wasn't back in Central's local committee, where the prevailing
sentiment was to prevent secondary overstress and minor damage, no matter
what. Consensus is elusive when nobody knows what objectives the next person
holds to, and when those goals aren't asked about.  The rhetorical test for
any proposal, "is it appropriate to our goals," can't be used when no goals
in common have been settled on.

========================
Those are my two reasons for there being a special seismic code purpose
statement. The first story tells of two radically different purposes in
effect in California simultaneously, for many decades. Much of the present
clash over residential woodframe seismic code is because SEAOC is dominated
by schoolhouse/ Field Act-oriented practitioners, but residential
construction procedures (with the minimal role of engineering input to it)
is so radically different as to be in a different world. And these
differences have firm  approval and backing in the state legislature. Sorry,
but there will have to be unprecedented new reliance on residential engineer
practitioners in seismic codewriting if conflict is to be resolved.  

The second reason's story tells of one re-enactment of the lesser seismic
purpose that is still in effect, although not everyone regards it as enough
any longer. What the seismic purpose in the future should be is a question
of public policy, not a technical committee's exclusive prerogative. The
present technical people on committee may, if diligent to their goals, be OK
at saying HOW to achieve performance objectives, in THEIR OWN areas of
design familiarity, but it does not follow that they should be permitted to
control anything beyond those.

Charles O. Greenlaw SE    Sacramento CA