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CIV100
Assignments
Section B/E
Fall 2011
Assignment 8
Due on Monday, November 14
th
2011
Draw a FBD if necessary; Pay attention to significant figures; A ruler is always required.
1 A gate in a saltwater canal is hinged at A as
shown, and held closed by the pinconnected
assembly CDE. The canal is 3.2m wide and the
density of the salt water is 1040 kg/m
3
.
Determine the minimum vertical tension force T,
required to keep the gate close. [2006 Final]
Solution:
Step1:
Draw the FBD
The thing you need to know is, the meaning of “minimum vertical tension force T applied at
point D, it means we have the breaking point for the system – the gate is just about to open, at
this situation,
there is no reaction force at point B
.
Step2:
Calculate water pressure
Ay
Ax
F
DC
F
DE
F
ED
=F
DE
F1
kN
w
F
m
kN
m
kg
N
m
kg
gz
w
35
.
110
)
2
.
3
)(
5
.
0
)(
6
.
2
(
1
/
526
.
26
)
6
.
2
)(
/
81
.
9
)(
/
1040
(
2
3
=
=
=
=
=
ρ
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View Full DocumentCIV100
Assignments
Section B/E
Fall 2011
Assignment 8
Due on Monday, November 14
th
2011
Draw a FBD if necessary; Pay attention to significant figures; A ruler is always required.
Step3
Analyze the FBD of the gate AEB, taking moment about point A, you will find force in member
DE.
Step4:
Solve the left segment (Joint D), you will find T.
T = 113.9 kN
2 The pinconnected (point A, B, D and E)
hoist system shown has a fixed support at C.
The cable from the load passes over the
frictionless pulley and is connected to the wall
at F. The pulley at D has a radius of 0.5m.
Determine the reaction components acting on
member ABC. Summarize your answers on a
separate free body diagram of ABC. [2003 Final]
Solution:
Separate all members and choose the right one to start (red means unknown). The only object has
at least one known and less than 3 unknowns is the pulley, after solving the pulley we get Dx and
Dy, then we can solve ADE, after getting Ey, Ax, and Ay, we can solve Cx, Cy, and M on
member ABC.
Step 1: FBD of all four objects
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