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Re: IBC First Draft Comment

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Dennis S. Wish wrote:
> 2308.2 (7): " Conventional light-frame construction shall not be used in
> irregular structures in Seismic Design Categories D and E, as specified in
> Section 2308.12.6."


Since at least 1979, (when I started engineering) there has been the
statement under conventional framing that stated that the provisions
didn't apply to buildings of "unusual shape, size or split levels.  In
the 88 UBC, Tables for structural irregularities were added.  I've used
the argument that the items defined in the structural irregularity
tables are considered the elements of unusual size, or shape and have
been able to educate the owner of the property enough that he/she is
willing and desires to pay for the structural design the building should

When using the conventional framing provisions, one must rely on the
span tables for rafters and I think they have been limited to 15 psf
dl.  There are tables for 30 psf ll for roof, which it appears will be
eliminated in the new code.  With regard to trusses, I've used the
argument that they are not outlined in the conventional framing section
therefore their use is not conventional framing.  And with the longer
spans, and therefore higher reactions, the bearing conditions need
examined.  This is especially true where you have a carrying truss at a
change in direction or change from trussed to conventional framing as is
common in so many prefab truss systems.

I am glad however to see the wording chang to specifically address the
irregularities as it  makes it easier to convince a stubborn contractor
who thinks we overdesign buildings.  This also gives the plan checker
something in black and white as to when an engineer is required.  I've
always taken the oppurtunity to "educate" plan checkers regarding my
interpetation of this first paragraph of the general construction
provisions and usually with success.
Steve Privett