Civil Engineering Reference
In-Depth Information
Determination of the chord force at grid lines 2B and 2C (see Fig. 4.12):
Section A:
wx
2
1
1
23 16
2
()
2
1
22
FRx
=
()
-
=
8684 16
()
-
=
5600
lb
2
B
1
2
D
sect
A
sect A
Section B:
wx
2
1
7
7716
2
()
2
1
16
FRx
=
()
-
=
6316 16
()
-
=
5700
lb
2
C
1
2
D
sect
B
sectB
As a point of interest, the reader should determine the shears and chord forces in
sections A and B at grid line 2 if a 200 plf uniform load is applied to section A only
instead of applying windward and leeward wind loads to sections A and B.
Hint: Sum vertical forces about the left side of grid line 2 toward grid line 1,
assuming that the diaphragm shears to the left side of grid line 2 are uniform, based
on the depth of the individual sections.
Determination of transfer diaphragm shears TD1 (see Fig. 4.13):
The chord force at grid line
B is in tension and is pulling on transfer diaphragm TD1. The chord force at grid line C
is in compression and is pushing on the transfer diaphragm.
=
-
5700 16
()
+
5600 34
()
1771 4
1
.
V
=
1771 4
.
lb
v
=
=
118 1
.plf
A
56
A
5
The transfer diaphragm reaction at A is acting to the right. Applying the remaining
shears on the sheathing element shows that the shear is negative.
=
-
5600 22
()
+
5700 40
()
1871 4
1
.
V
=
1871 4
.
lb
v
=
=
124 8
.plf
D
D
56
5
The transfer diaphragm reaction at D is acting to the left. Applying the remaining shears
on the sheathing element shows that the shear is also negative.
3828 6
15
.
VVF
=- =
1871 4
.
-
5700
=-
3828 6
.
lb
v
=
=+255 24
.
lf
CD C
2
C
The shear crosses the line, therefore it becomes positive.
V
B
=-
3828 6
.
+
5600
=
1771 4
.
lb
therefore Ok
Determination of diaphragm net shears (see Fig. 4.13):
The net shears in the transfer
diaphragm are calculated as follows:
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