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RE: Prescriptive Residential Construction Vs New Design Standards; Curee-Caltech Project

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Dennis, without disputing the areas for clarification you suggest, I submit
that it is the SE professionals who least understand the interface between
carpenter-built customary woodframing and engineered woodframing.

That 1985 act of the legislature that I posted yesterday (and a year ago)
has a key word: PORTIONS. The framing part of the woodframe residence is
divided up between prescriptive and engineered portions. Professionals seem
loath to understand that. SEAOC-affiliated professionals whom I have
encountered in committee work are particularly reluctant to let a project
proceed on a split ticket. Their code change proposals are constantly
jiggered to convert great swaths of the scope of framing into the engineered
category because a single element in it deviates from the letter of
"conventional" construction, and when everyone on the committee knows how to
engineer a simple, localized cure for the inadequacy in the deviating element.

Professionals carry on as though all the framing should be engineered and
subject to verified reports like in Field Act work on public schools. Maybe
it should be that way in the most treacherous seismic areas. The legislature
however has not supported that view, and each year legislators attempt to
scale back the scope of the Field Act as well. If Building Officials are
less willing to demand engineering content than engineers would like, it
suggests that they are thinking more like the elected legislators do than
like the engineers do.

Other non-professionals who aren't in doubt are the residential contractors
and framers. Much of their knowledge is from learning on the job, where
engineering is for parts and pieces here and there, and the rest is done the
way framers, inspectors, tradition, and relevant code prescriptives agree it
should be done. Who plans on changing that principle? 

The big problem with SE professionals tinkering with house framing
prescriptives is their insistence on applying box-shaped commercial building
and schoolroom modeling and metaphors to residential construction features
that markedly differ. An example is roof "diaphragms".

One reason the "body count" is low in old house top stories is that the roof
is only a flimsy weather shelter of wood shingles on spaced board sheathing
on widely spaced rafters. But connecting all the many walls is a flat
ceiling of plaster on lath under joists heavier than the rafters. The
diaphragm is the ceiling. Not the strongest stuff, but not stressed out too
bad in most locations in the state. Professional SE's would ignore that
ceiling and complain about the skip sheathing way up top where no
cross-walls reach. Put differently, the diaphragm across the top of our
heads is our skull, not our hat. San Francisco was a big town in 1906. How
many woodframe houses had "real" roof diaphragms that cross walls conected
through attics to, compared to mere plastered ceilings those cross walls did
reach? And how many top stories collapsed? Look at the photos taken before
the fire came through.

The point here is that conventional features of woodframe construction can
have load paths and useful value that SE professionals typically remain
blind to, and which replace the commercial building idealizations SE's are
habituated to but can't find in houses. 

Just maybe the professors in the Curee-Caltech inquiry can shelter
themselves from design professionals and "professional code changers" long
enough to establish an independent structural perspective of their own. They
are going to have to go out and get pitch and slivers in their hands, and
get friendly with framers, though. There isn't much wood framing up in ivory
towers.

Charles O. Greenlaw, SE   Sacramento CA

[as cited above]
>Sec 6737.1(b) of Cal Business and Professions Code (the PE Act) provides as
follows: "If any PORTION of any structure exempted by this section deviates
from substantial compliance with conventional framing requirements for wood
frame construction found in ...[the building code]...the building official
having jurisdiction shall require the preparation of
plans,drawings,specifications,or calculations FOR THAT PORTION by,or under
the direct supervision of,a licensed architect or registered engineer." The
same language appears in the Architects Practice Act at sec 5537, and is
reprinted in the big reference book the Contractors Board publishes on the
Contractors License Law. These boards have continuing outreach programs to
educate building officials on these laws and the need to enforce them.
>