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[SEAOC] 1994 UBC Conventional Framing Section - Opinions Wanted

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The 1994 UBC grants provisions for non-professionals to design and 
construct light framed wood structures for residential use. This section 
of the code provides a prescriptive measure, which when followed, 
assumes that the structure is adequately tied together. Cities such as 
Los Angeles, adopt similar measures and provide typical construction 
sheets (Typical Type V) which tell the builder / designer which gravity 
load members to use for specific plans and how to sheath and anchor 
braced panels in place.

Most of the larger cities have, since the Northridge Earthquake, opted 
to be more discriminating in the definition of conventional 
construction. This is done by providing a degree of ambiguity into the 
definition of "conventional" framing.  The 1994 UBC, however, has 
removed some of the a ambiguity by tightening up the definition of the 
code as well as expanding it?s interpretation to multistory, unusually 
shaped structures with non-stacking shear elements(Section 2326.5.4).

In the many smaller municipalities throughout each state, the question 
of the building official?s authority is of great concern.  The code does 
not identify the political cycle that often ties the hands of the 
building official against their better judgment.  Specifically, new 
construction brings revenue to each city in the form of building fee?s, 
utility, infrastructure and school taxes.  A developer of individual 
home-sites is an asset that most towns try to protect - right down to 
the city council.  Without support from city council members, building 
officials often can not over-rule published codes, even if written 
incorrectly.

Section 2326 - Conventional Light-Frame Construction Provisions of the 
UBC (1994) is one such poorly written code. Although the section 
adequately covers gravity load members, it does not clearly define 
lateral load connections from roof to foundations. Cross references to 
Chapter 16 of the code are greatly deficient except where the structures 
do not conform to the provisions defined in "Conventional Framing".

A brief summary of the provisions of this section is as follows: Please 
note that sections 2326.1 through 2326.4 define the preamble to the body 
of this section of the code - establishing which structures conform to 
"conventional framing" definitions. I start with section 2326.5 since it 
is specific to Seismic Zone 4 ; 
1. 2326.5.1 defines the maximum spacing of the braced panel.
2. 2326.5.2 defines the maximum loading to gravity members (rafter 
spans) and indicates that if the loads exceed these values an 
engineering design shall be provided.
3. 2326.5.4 provides a far less restrictive definition of 
non-conventional and, in fact, extends the term conventional to include 
two story wood framed residential structures.
4. 2326.5.4.3 provides a means to attach a shear wall to a header, but 
makes no provisions for resistance to uplift
5. 2326.5.6  defines Interior braced wall supports - requiring a 
continuous foundation under the walls at interval not exceeding 50 feet 
with EXCEPTIONS
6. 2326.6 defines mud sill anchorage
7. 2326.7 requires beams and girders to be bearing and indicates the 
depth of girders in single story construction by opening width.
8. 2326.8.1 defines gravity load framing details, including blocking and 
framing around openings, sub-floor sheathing and horizontal wood 
structural panels (2326.9.2).
9. 2326.11 defines Wall Framing - stud size, spacing, maximum height for 
bearing and non-bearing conditions and plate lap splices.
10. 2326.11.3 defines bracing - with minimum requirements for panel 
width to height limitations, minimum sheathing, anchorage and hold down 
requirements.
11. 2326.11.4 provides a more severe ALTERNATIVE to the previous section 
by defining plywood shear wall panels - sheathing, nailing, and tie-down 
devices

The remainder of the section defines roof and ceiling framing - with 
very little difference over the 1991 code. So WHAT IS THE PROBLEM?

UBC does not provide links to establish adequate ties of the diaphragms 
to shear resisting elements. By this I refer to the load path of the 
diaphragm to foundation (ie; diaphragm connection to shear element 
(except at the perimeter bearing), drags and collectors, chords etc).
1. Braced walls are only defined to have connection to foundations, but 
fail to address the connection of the wall panel to the diaphragm above. 
 
2. Where wind loads predominantly govern, discussions of drags and 
collectors to interior braced walls are deficient. For a one story home 
fifty feet in width - the interior braced panel will take almost fifty 
percent of the lateral load. Assuming a typical scenario with a 70 mph 
wind - assume a 16 psf load, the approximate load to the wall will be in 
the neighborhood of 2800 lbs.  Following section 2326.11.4 for a minimum 
2.67 ft panel 10 feet in height, the unit shear would be 1048 plf. The 
provisions in the section require a 3/8" thick CDX panel w/ 8d at 6" on 
center assumed blocked by vertical layout of the panel (top and bottom 
plate connections at the panel ends).   This section of the code 
requires resistance to uplift of 1800 lbs, but the actual uplift where 
framing is parallel to the wall can be closer to 10,000 lbs if the dead 
load is ignored.
3. This provision assumes that the builder is familiar with this section 
of the code. A false assumption since current requirements for licensing 
of general contractors does not require nor test for  the understanding, 
or compliance to conventional framing codes.

I believe my point is clear. The UBC provides a means for the allowance 
of unacceptable building construction standards. In area's outside the 
large city, inspectors are not adequately trained to locate 
discontinuities of shear transfer.  A building official who wishes to 
negate this section of the code faces an uphill battle with local 
administrators (city council, construction developers, mayors office 
etc.) who have more to gain from revenue developed through profitable 
construction than potential effects of improper construction technique. 
Developers threaten to move their projects to other, more liberal 
communities. Once this happens, the building official has very little 
ammunition to fight with since the provisions are published, and 
accepted by the building industry.

In the May edition of  SEAOSC?s  newsletter, the President?s message 
addressed a somewhat similar issue. I was abhorred to read that Mr. 
Ranous considered the inconsistencies to be best left to the ethics and 
conscience of individual engineers rather than to be addressed by the 
structural engineering community as a whole.
It is just these issues that need to be addressed by the professional 
community. We must remember that these codes are adopted by votes from 
many different professional communities - not simply the structural 
profession. SEAOC has a very limited number of votes within ICBO and it 
is therefore extrememly urgent that the community act professionally to 
communicate our concerns for the publication of codes such as this.
I apologize for the length of this letter, but I am interested in your 
comments and have been asked (by two life members of SEAOC) to draft a 
letter to the state urging a united stand against inadequate code 
provisions.  Please start a thread with this message and provide me with 
your thoughts, idea?s and any other comments you may have. If you 
disagree, please let me have your comments as well.

Sincerely,
Dennis S. Wish PE
Editor SEAOC Online

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