QUIZ #1 – Solution
A simple pinconnected truss is loaded and
supported as shown in Fig. P1.11. All
members of the truss are aluminum pipes that
have an outside diameter of 4.00 in. and a wall
thickness of 0.4 in.
Determine the normal
stress in member AB.
Fig. P1.11
Solution
Overall equilibrium:
Begin the solution by
determining the external
reaction forces acting on the
truss at supports
A
and
B
.
Write
equilibrium equations that
include all
external
forces.
Note that only the external
forces (i.e., loads and reaction
forces) are considered at this
time.
The internal forces acting
in the truss members will be
considered after the external
reactions have been computed.
The freebody diagram (FBD)
of the entire truss is shown.
The following equilibrium
equations can be written for this
structure:
2 kips
2 ki
0
ps
x
x
x
F
A
A
Σ
=
+
=
∴
= −
(6 ft)
(5 kips)(14 ft)
(2 kips)(7 ft)
14 kips
0
y
A
y
B
B
M
Σ
=
−
−
∴
=
=
5 kips
0
9 kips
y
y
y
y
F
A
B
A
∴
= −
Σ
=
+
−
=
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 Fall '11
 Weng
 Force, Stress, reaction forces, kips, kips FAC, kips ΣM

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