Civil Engineering Reference
In-Depth Information
Chord forces at grid line A, summing from grid line 1:
Location (Grid Line)
Force
79 4194
2
.
+
.
A at 2
F
2
=
()
15
=
740 6
.
lb compression
A
610 6
.
+
463
A at 3
F
3
=
740 6
.
+
()
12
=
7182 2
.
lb compression
A
2
463
+
315 4
2
.
A at 4
F
4
=
7182 2
.
+
()
12
=
11 852 6
,
.
lb compr
ession
A
A at 5
F
5
=
11 852 612
,
.
+
.
-
404 811 449
.
=
,
lb compression
A
Chord forces at grid line D, summing from grid line 1:
Location (Grid Line)
Force
187 2
.
+
127 2
.
D at 2
F
2
=
()
15
=
2358
lb tension
D
2
430 9
.
+
315 4
.
D at 4
F
4
=
2358
+
()
24
=
11 313
,
lb tension
D
2
D at 5
F
5
=
11 313
,
+
184
-=
64
11 433
,
≅
11 448
,
lb calculated
D
The analysis shows that the net diaphragm shears in the areas located between grid
lines 1 and 2 from A to B, between grid lines 1 and 2 from C to D, between grid lines 4
and 5 from A to B, and between grid lines 4 and 5 from C to D have been reduced below
the basic unit shears for a diaphragm without an opening. The magnitude of the shear
suggests that these areas can be unblocked with a 6″ o.c. edges and 12″ o.c. intermediate
nailing pattern. However, the aspect ratio of the transfer diaphragm is equal to
50
15
A..
==
3331
.
:
which requires the transfer diaphragms to be blocked. All other areas have increased in
shear and should be nailed accordingly. All the shears have been verified. Accordingly,
all the chord, strut, and collector force diagrams have closed to zero, which verifies that
the analysis is correct.
▲
5.4
Diaphragm Deflection
ATC 7 noted that the introduction of an opening in a diaphragm has no effect on the
deflection contributed by the flanges. There is a small contribution due to bending
when web openings occur in actual diaphragms, but this is not reflected in the equation
since all bending is assumed to be resisted by the flanges. The shear stresses in the
remaining sections of the diaphragm on either side of the opening are increased since in
normal construction practice there is less web material available. The effect of an open-
ing on the deflection is determined from classical analysis used to derive the second
term of the equation (shear deflection), using integrations over segments of the dia-
phragm. The procedure for designing diaphragms for nonuniform loads is the same as
that for any beam subject to these loads. The determination must be done on the basis
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