Civil Engineering Reference
In-Depth Information
This force is transferred into transfer diaphragm TD1.
Before the force between grid lines 4 and 5 can be determined, transfer diaphragm
TD2 shears must be calculated because the transfer diaphragm receives the disrupted
chord force at grid line 4D and transfers part of that force into its support at grid line B.
Part of the combined basic diaphragm shear and transfer diaphragm shear forces that are
applied into the collector at grid line B are shared by transfer diaphragms TD1 and TD3.
F
chord
= 3000
lb
Transfer diaphragm shears (Fig. 8.9, lower right):
V
D
3000 10
50
()
600
15
B
TD
V
=
=
600
lb
v
=
=
=−
40
plfnega
tive shearatgrid lineB
B
B
V
D
3000 40
50
()
2400
15
E
TD
V
=
=
2400
lb
v
=
=
=+
160
plfpositiveshear at gri
d lineB
E
Add the basic diaphragm shears with the transfer diaphragm shears to determine
the net shears within TD2.
Grid line 4, from B to D:
v
=−
60 22
.
− −
(
40
)
100 22
.
plf
Grid line 5, from B to D:
v
=−
83 33
.
− −
(
40
)
123 33
.
plf
Grid line 4, from D to E:
v
=−
60 22
.
+
(
160
)
= +
99 78
.
plf
Grid line 5, from D to E:
v
=−
83 33
.
+
(
160
)
= +
76 67
.
plf
The force in the collector between grid lines 3 + 10′ and 5 is
100 22
.
+
123 33
.
F
=
()
15
=
1676 6
. btension
2
Applying these forces to the transfer diaphragms and completing the longitudinal
chord/collector force diagrams will show that the diagrams at grid lines B, D, and E do
not quite close to zero. By trial and error, it can be seen that 550 lb actually goes to TD1
and 1783.3 lb goes to TD3. The force applied to TD1 is in compression, and the force to
TD3 is in tension.
Transfer diaphragm TD1 (see Fig. 8.10):
The disrupted chord force and collector forces at
the edge of the opening are applied to transfer diaphragm TD1 as shown in the figure.
∑
M
D
=
0
1
80
V
A
=
[(
5250
+
550
)(
40
)
+
2043 70
(
)]
=
4687 63
.
lb
V
D
4687 63
20
.
v
=
A
TD
=
=−
234 4
.
plfnegativeunitshe
ar
A
∑
M
A
=
0
1
80
V
D
=
[(
5250
+
550
)(
40
)
+
2043 10
(
)]
=
3155 4
.
lb
V
D
3155 4
20
.
v
=
D
TD
=
=+
157 8
.
plfpositiveunitshea
r
D
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