inch
(150mm)
and
8-inch
(200mm)
boards,
(7.5m) may have a depth equal to the width.
respectively, at the diaphragm boundaries. End joints
(b) Where calculations show that diaphragm
in adjacent boards will be separated by at least two
deflections can be tolerated, the depth normal to the
joist or stud spaces, and there will be at least two
open end may be increased to a depth-to-width ratio
boards between joints on the same support.
The
not greater than 1:1 for diagonal sheathing, or 2:1
boundary or chord members at the edges of
for
special
diagonally
sheathed
or
plywood
diaphragms will be designed to resist direct tensile
diaphragms.
and compressive chord stresses.
This category of
diaphragms will also be considered very flexible;
(4) Material requirements.
such diaphragms will not be used for the lateral
(a) Straight sheathing. Straight sheathing
support of masonry or concrete walls.
diaphragms will be constructed of 1- or 2-inch (25 or
2.
Special
construction.
Special
50mm) nominal boards, 6 or 8 inches (150 or
diagonally sheathed diaphragms will include two
200mm) nominal in width, with boards laid at right
adjoining layers of 1-inch (25mm) nominal sheathing
angles to the rafters or joists. Boards will be nailed
boards laid diagonally and at 90 degrees to each
to each rafter or joist and to peripheral blocking with
other. Special diagonally sheathed diaphragms also
two 8d common nails for 1-inch by 6-inch (25 x
include single-layered diaphragms, conforming to
150mm) and 1-inch by 8-inch (25 x 200mm)
conventional construction, and which, in addition,
sheathing. For 2-inch (50mm) sheathing, nails will
will have all elements designed in conformance with
be three 16d. End joints of adjacent boards will be
the following provision: each chord or portion thereof
separated by at least two joist or rafter spaces, with at
may be considered as a beam loaded with a uniform
least two boards between joints on the same support.
load per foot equal to 50 percent of the unit shear due
They will not be used for the lateral support of
to diaphragm action. The load will be assumed as
masonry, concrete, or other walls that would be
acting normal to the chord in the plane of the
seriously affected by high floor-to-floor deflection.
diaphragm, and either toward or away from the
Straight sheathing diaphragms are permitted only for
diaphragm. The span of the chord, or portion thereof,
buildings in Seismic Design Category A or B.
will be the distance between structural members of
(b) Diagonal sheathing.
the diaphragm, such as joists or blocking, which
serve to transfer the assumed load to the sheathing.
1.
Conventional construction.
These
Special diagonally sheathed diaphragms may be used
diaphragms will be made up of 1-inch (25mm)
to resist shears due to seismic forces, provided such
nominal sheathing boards laid at an angle of
shears do not stress the nails beyond their allowable
approximately 45 degrees to supports.
Sheathing
safe lateral strength. For approximating deflections,
boards will be nailed directly to each intermediate
a value of F of 75 will be used; thus, special
bearing member with not less than two 8d nails for 1-
diagonally sheathed diaphragms also fit into the
by 6-inch (25 x 150mm) boards and three 8d nails for
category of flexible diaphragms.
boards 8 inches (200mm) or wider, and in addition,
three 8d nails and four 8d nails will be used for 6-
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