Civil Engineering Reference
In-Depth Information
e
n
= nail deformation, in
G
t
= panel rigidity through the thickness, pounds per lineal inch, pli, of
panel width
L
= length of diaphragm, ft
V
= maximum shear due to design loads, plf
∆ = calculated deflection, in
Σ∆
(
C
X
= sum of individual chord splice slip values on both sides of the
diaphragm, each multiplied by its distance to the nearest support
)
The first term of the equation represents the bending deflection, the second term
represents the shear deflection, the third term is for the contribution of nail slip, and the
last term is for chord splice slip. The deflection calculated is based on the assumption
that the maximum deflection occurs at midspan. The deflection of an unblocked dia-
phragm is approximately 2.5 times the deflection calculated above if the spacing of the
framing is 24″ o.c. or less and 3.0 times if the framing spacing is more than 24″ o.c., as
noted in IBC Section 2305.2 (commentary) and the APA
Design and Construction Guide
—
Diaphragms and Shear Walls.
5
The deflection of the diaphragm will significantly increase
if the nail spacing increases as it gets closer to the centerline of the diaphragm, as it
typically does. The constant of 0.188 in the nail slip term of the equation applies to dia-
phragms with uniform nailing only. ATC 7 recommended that whenever a variation in
nail spacing occurs, the constant be increased in proportion to the average load on each
nail with nonuniform nailing compared to the average load that would be present if
uniform nail spacing had been maintained (see Fig. 3.7).
V
V
′
n
n
0 188
.
where
V
n
′ = average nonuniform load per nail and
V
n
= average uniform load per nail.
F
i g u r e
3.7 Delection, nonuniform nailing. (
Courtesy, APA—The Engineered Wood Association.
)
Search WWH ::
Custom Search