Need a book? Engineering books recommendations...

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

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

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Chuck,
I think that we are lost in the rhetoric here. The problem is not so dire,
it just needs to be clarified so that non-professionals understand it.
Conventional framing has certain restrictions that must be met to stay in
compliance. Use these restrictions to clean up the missing information in
the code:
1) Trusses or roof framing can not exceed 34'-0" clear span. Let's assume
that the clear span distance is 40' and that eaves typically extend 30
inches past the face of the building. Assume a maximum tributary width plus
overhang and create a span table to choose headers.
I have been told that most contractors over-design these historically. I
have found the opposite to be true as the cost of wood rises.
2) Clearly state and show by simple drawn examples how an interior braced
wall is connected to the roof diaphragm. Define the load path so it is
understood.
In many cases the interior braced panel will have a greater uplift potential
than exterior panels since they can exist parallel to framing. Increase the
minimum tensile  connection and clearly state it in the prescriptive method
3) Presently, the only place a tension connection is required is in the
narrow piers at each side of the garage opening. This is because 4'-0"
panels can be installed in compliance with section 2320.11.3. This section
does not require the use of a tension strap or hold down at the ends.
Narrow panels will not comply with 2320.11.3 and fall under the provisions
of 2320.11.4 - Alternative Braced panels. This is the only place that
requires the installation of mechanical holddown devices.
In most cases (especially if a tile roof is installed) the numbers will show
that uplift occurs on minimum width panels that are defined in 2320.11.3.
Simply add the same verbiage that exists in the section on Alternative
Braced panels (2320.11.4) and resolve the problem by adding a minimum
tension resisting strap.
4) Alternative braced panels, as I mentioned, are used at the garage piers
and are often 2'-8" wide x 8'-0" tall. The problem is that the foundation is
not continuous across the opening which may create an unstable foundation.
The solution is to require a continuous beam at the front of the garage.
5) The provisions for braced panels does not clearly indicate that panels
are not to be perforated. Seems obvious but is often abused. It's
interesting that in my location electrical panels are placed at the rear
corner of the home - just where the code requires a braced panel.

One of the biggest problems related to Conventional Framing is the fact that
the section is written for professionals  but is expected to be used by
lay-persons. This must be true since there is no other publication, that I
am aware of (with the exception of the City of Los Angeles Type V Sheet),
where these provisions are either graphically illustrated or which are
written in a language easily understood by the contractor or homeowner.
If ICBO intends this section to be a prescriptive methodology then why not
combine the requirements into one easy to understand document? Cost?
Economics? Politics? Are any of these reasons justifiable at the expense of
either the insurance industry or the home-owner. Professionals are familiar
with the deficiencies and nothing has been done until FEMA issued a 5.6
Million dollar grant with a preface that clearly identifies "approximately
half of the property losses were incurred by damage to woodframe
construction". It didn't take "bodies". The economics were sufficient enough
to attack all of us where it hurts the most - our pocketbooks.

So far, I've suggested a few very simple changes that would comply with
conventional standards which, does not require the involvement of a
professional architect or engineer that, does not "drum up" work for
professionals and would significantly help to improve construction quality.

It puzzles me as to why these deficiencies are defended so strongly. The
intention of the prescriptive code is an admirable attempt to provide
quality, affordable housing? Yet, ICBO has abandoned this section of the
code while there is still some five or six years left in the enforceable
cycle?
While the FEMA study is underway, we could be helping by simply addressing
these problems and issuing intermediate corrections which may have a
profound affect upon the reduction of damage in imminent seismic events.

Dennis Wish PE