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Re: Prescriptive Residential Construction Vs New Design Standards; Curee-Calt...

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I agree with Charles. The conventional framing provisions of the UBC is the
best compromise we can get. We(structural engineers) have been constantly
trying to improve these provisions to conform 100% to our standards and every
code revision, there has been improvements. And we should continue doing so. 

I am one of those engineers willing to stick my neck out and take the risk of
lawsuit if one of my room addition/remodel jobs fail because I leave existing
framing as-is knowing it does not calc out. I just calc out the new framing
system. Even if part of my new framing system does not calc out, if it
conforms to the Conventional Framing Provisions, its OK with me. Most of my
jobs are room additions. Somebody has to do the dirty, low paying jobs.

Engineered buildings that calcs out assumes the ideal framing system. It does
not take into consideration the other portions of the framing system that we
assume do not resist any load. A conventional house basically is an
indeterminate structure. But to be able to calc it out, we assume simple beam
design of rafters, joist and beams assuming that the plywood sheathing and the
drywall ceiling does not exist. To calc out kickers with purlins to roof
rafters, we assume that we have isolated rafters, purlins, kickers,rafter ties
and only the nails hold them together. We neglect the plywood sheathing
distributing the load to the exterior wall top plates nailed to other ceiling
joists with drywall. To calc out simple span hip beams, we neglect the kick-
out resistance provided by the plywood sheathing distributing the load to the
top plates that are lapped at the corner. And as Charles said, and I talked
about it on my previous post, the interior braced wall transfer lateral load
to the drywall ceiling to the ceiling joists to the rafter to the top plate,
etc. Also, the top plates in bending distributes some of the lateral load to
the interior walls that are not too far apart. All of these minor transfer
mechanisms does not calc out but it sure does contribute something. These may
be the reason old houses do not fall down.

By the way, Dennis, ICBO has a book titled "Illustrated Guide to the
Conventional Construction Provisions of the Uniform Building Code" It is for
the 1994 UBC, about 193 pages, with a lot of illustrations and explanations.
These might not be simple enough for all framers but a framing foreman would
definitely understand it and will be able to guide his framers accordingly. We
can use this book as a starting point, improving on it, and recommend to have
it included as part of every building department's guidelines.

I am personally more worried about the house being built per plan(assuming the
plans are complete) than making sure the plans are based on exact
calculations. I would put more emphasis on requiring structural observation on
all houses than requiring all houses to calc out.

Just my opinion.

Ernie Natividad