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Problem 6.111 The four-bar linkage operates the forks
of a fork lift truck. The force supported by the forks is
WD8 kN. Determine the reactions on member CDE.
0.7 m
0.15 m
0.2 m
0.15 m
0.2 m
0.2 m
0.3 m
Forks
W
E
D
A
F
C
B
Solution: Consider body BC. Note that AB is a 2-force body.
Fx:CxD0
W = 8 kN
486
Problem 6.112 If the horizontal force on the scoop is
FD2000 lb, what is the magnitude of the axial force
in the hydraulic actuator AC?
10 in 12 in20 in
B
C
D
A
38 in
28 in
10 in
Scoop
F
Solution: We start with the free-body diagram of the scoop. Note
that BC is a two-force body. The angle
Problem 6.113 A 10-kip horizontal force acts on the
bucket of the excavator. Determine the reactions on
member ACF at Aand F.
Bucket
2 ft 3 ft
2 ft
9 ft
2 ft E
F
D
B
A
C
4 ft 4 in
5 ft 6 in
1 ft 8 in
1 ft 4 in
10 kip
MA:⊲10 kip⊳⊲66 in⊳
488
Problem 6.114 The structure shown in the diagram
(one of the two identical structures that support the
scoop of the excavator) supports a downward force FD
1800 N at G. Members BC and DH can be treated as
two-force members. Determine the reactions on member
CDK at K.
H
LK
100
mm
160
mm
Shaft
260
mm
320
mm
380
mm
200
mm
C
D
1040
mm 1120
mm
260
mm
B
J
180
mm
Scoop
G
F
Solution: Start with the scoop
MJ:4
p17 FBC⊲0.44 m⊳1
p17 FBC⊲0.06 m⊳
Now examine CDK
MK:56
p3161 FDH⊲0.26 m⊳4
p17 FBC⊲0.52 m⊳D0
Problem 6.115 The loads F1D440 N and F2D160 N.
Determine the axial forces in the members. Indicate
whether they are in tension (T) or compression (C).
B
200 mm
400 mm
A
F1
700 mm
F2
C
Solution: The sum of the moments about Cis
490
Problem 6.116 The truss supports a load FD10 kN.
Determine the axial forces in the members AB,AC,
and BC.
B
3 m
A
4 m 3 m
D
C
F
Solution: Find the support reactions at Aand D.
Joint A:
y
θ
Problem 6.117 Each member of the truss shown in
Problem 6.116 will safely support a tensile force of
40 kN and a compressive force of 32 kN. Based on this
criterion, what is the largest downward load Fthat can
safely be applied at C?
492
Problem 6.118 The Pratt bridge truss supports loads
at F,G, and H. Determine the axial forces in members
BC,BG, and FG.
BC D
4 m
60 kN 80 kN 20 kN
FG H
E
A
from which ED70 kN. The sum of the forces:
FxDAxD0.
FyDBF 60 D0,
from which:
AB sin ˛BF BG sin ˛D0.
Solve: BG D42.43 kN ⊲T⊳ ,
and AB cos ˛CBC CBG cos ˛D0,
from which BC D120 kN ⊲C⊳
60 kN
Joint AJoint FJoint B
Ay
AB
AB BF
BF
BG
BC
AF AF FG
ααα
Problem 6.119 Consider the truss in Problem 6.118.
Determine the axial forces in members CD,GD,
and GH.
Solution: Use the results of the solution of Problem 6.130:
CG GD
BG
494
Problem 6.120 The truss supports loads at Fand H.
Determine the axial forces in members AB,AC,BC,BD,
CD, and CE.
AI
200 lb
F
100 lb
H
J
E
D
CG
B
4 in
6 in 6 in 6 in 6 in
4 in
4 in
Solution: The complete structure as a free body: The sum of the
moments about I:
The method of joints: The angles of the inclined members with the
horizontal are
200 lb
in
in
in
AB
CD
CE
AC BD
αα
Problem 6.121 Consider the truss in Problem 6.120.
Determine the axial forces in members EH and FH.
Solution: Use the results from the solution to Problem 6.132:
DF 200 lb
EF
EH
DE
α
496
Problem 6.122 Determine the axial forces in members
BD,CD, and CE.
2 m
2 m
2 m
2 m
A
C
E
G
I
6 m
D
B
F
H
10 kN
14 kN
Solution: Use the method of sections
FBD FCD FCE
1.5
D53.13°
Problem 6.123 For the truss in Problem 6.122, deter-
mine the axial forces in members DF,EF, and EG.
Solution: Use method of sections
A
2 m
A
10 kN
498
