2308.12.6 Irregular structures. Conventional light-frame
construction shall not be used in irregular portions of structures
in Seismic Design Category D or E. Such irregular
portions of structures shall be designed to resist the forces
specified in Chapter 16 to the extent such irregular features
affect the performance of the conventional framing system.
A portion of a structure shall be considered to be irregular
where one or more of the conditions described in Items 1
through 6 below are present.
1. Where exterior braced wall panels are not in one plane
vertically from the foundation to the uppermost story
in which they are required, the structure shall be considered
to be irregular [see Figure 2308.12.6(1)].
Exception: Floors with cantilevers or setbacks not
exceeding four times the nominal depth of the
floor joists [see Figure 2308.12.6(2)] are permitted
to support braced wall panels provided:
1. Floor joists are 2 inches by 10 inches (51mm
by 254 mm) or larger and spaced not more
than 16 inches (406 mm) o.c.
2. The ratio of the back span to the cantilever is
at least 2:1.
3. Floor joists at ends of braced wall panels are
doubled.
4. A continuous rim joist is connected to the
ends of cantilevered joists. The rim joist is
permitted to be spliced using a metal tie not
less than 0.058 inch (1.47 mm) (16 galvanized
gage) and 11/2 inches (38 mm) wide
fastened with six 16d common nails on each
side. The metal tie shall have a minimum
yield of 33,000 psi (227 MPa).
5. Joists at setbacks or the end of cantilevered
joists shall not carry gravity loads from more
than a single story having uniform wall and
roof loads, nor carry the reactions from
headers having a span of 8 feet (2438 mm) or
more.
