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IBC Conventional Framing

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Rick,
Who do we notify to alert the committee of corrections that need to be
addressed. For example; Figure 2308.12.6.6 "Braced wall Panel Extension over
Opening" should be numbered 2308.12.6.5.
I also have other questions (comments) about the section 2308.
1. The code limits plated trusses to 35' bearing to bearing. The code is
specific about shear transfer at perimeter walls bearing trusses. Assume the
truss is designed as a two span truss where the distance between supports
does not exceed 35'. Where is the reference in the code for shear transfer
through the center bearing wall (assuming that the load bearing on the wall
has a lateral component that the wall needs to resist)?
2. How does the IBC address the shear transfer from diaphragms at each side
of a wall that occur from what is traditionally called "California Framing".
The upper gabled roof dies into the lower gabled roof (which also supports
the ends of the high rafters. A discontinuity occurs between the lower
diaphragm attached to the bearing wall or shear wall below, and the high
roof that does not make a positive connection to the wall. This is still
considered Conventional framing (unless the IBC wishes to restrict this type
of framing from the Conventional definition). Typically a pony wall is
constructed above the lower roof and the upper roof is blocked to it and the
wall sheathed. This is one problem area that commonly occurs in conventional
construction (or engineered products). I would possibly consider this a roof
irregularity.
3. Section 2308.3.4 under exception does not address where in the code to go
when an intermediate bearing wall is provided under trusses and the wall is
used to resist the lateral component of the reaction.
4. Section 2308.3.2(3) - blocking should be defined as full height to avoid
a space between the block and the sheathing where a sloped roof occurs and
the conventional block is not set tight to the sheathing. This happens
often.
5. The code states that the blocking should be nailed to the top plate of
the wall, but does not state that the blocking shall rest above the top
plate. Therefore it is also seen where the block is placed outside the plane
of the wall for a stucco and eave support and the contractor tries to nail
through the block into the plate but does not provide the penetration, or
splits the block in his attempt. If the block is to be nailed outside the
plane of the wall, mechanical connectors should be used to connect the block
to the plate (such as an A35).
6. Section 2308.3.2(4)- possibly one of the most misunderstood sections on
drag struts - mostly where plated trusses are installed. First, it should be
made clear that the truss must be designed in accordance with the section of
the code that specifies it to be designed for drag forces or sheathed.
Second, it is most important to specify that the truss (or drag strut) be
placed in the plane of the wall. Often the spacing of trusses and rafters
will put the drag truss eccentric to the wall. In this case, the contractor
does not have an effective means to connect the truss to the wall unless he
calls an engineer into to provide a fix. Therefore on a prescriptive design
it is important to emphasize the location of the drag element to be placed
in the plane of the shearwall below. Problem area's occur at the back wall
of a garage used for shear to comply with the maximum braced wall framing.
In this example, if the roof gable changes direction two problems can
occure. First the truss parallel to the wall may be eccentric to the wall to
allow full bearing of the trusses perpendicular to the wall. The second
potential problem is that the trusses perpendicular to the wall are properly
blocked and sheathed but the upper gable dies into the lower gable by
"California framing" and a lack of shear transfer occurs. This can be
rectified in two ways. Assure the bearing wall below to be 2x6 construction
and that the drag truss bears on the wall as well as the perpendicular
trusses (which requires the shear to be transfered from both diaphragms.
OR, the truss parallel to the wall be designed as a girder truss to bear the
weight of the perpendicular trusses on the bottom chord. Even in this case,
proper shear transfer must be maintained.

Rick, the IBC discusses plan irregularity, but does not seem very clear on
shear transfer where gables are framed on top of one another. I can provide
you with drawings separately that will show these various conditions
accepted as "Conventional Framing" by local building departments.

One final question - If an alternative shear element needs to be provided
(such as an embedded pole or steel frame), is the entire structure forced to
comply with chapter 16 lateral and wind requirments by design (based upon
the definition of plan irregularity) or can this one element be designed as
a component while the rest of the structure complies to Conventional
Framing? If so, is the the engineer or architect free from liability for
everything but that which he/she designs?

Enough for now - A lot of good work went into this section, but I like to
think that the need to interpretate the sections can be reduced to bare
necessity.

Thanks to ICBO for providing the draft to us for OUR review.

Dennis Wish PE

|-----Original Message-----
|From: Richard_Ranous/OES(--nospam--at)oes.ca.gov
|[mailto:Richard_Ranous/OES(--nospam--at)oes.ca.gov]
|Sent: Friday, March 06, 1998 11:00 AM
|To: seaoc(--nospam--at)seaoc.org
|Subject: Re: duplication of plans
|
|
|
|Bill,
|
|In many respects I agree with you 100 percent.  I do have to say that the
|work SEAOC did on conventional framing was an attempt to address the
|concerns of zone 4.  Kelly Cobeen, Jim Russell, the housing task force, and
|others did calculations and justifications for panel lengths, spacings,
|locations, sill bolt size and spacing, etc.
|
|Conventional framing is an approach that will remain in the building codes
|and will have to be modified a little at a time.
|
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