CEN 202- Quiz #1 -B
Problem 1. (65 points)
A simply supported truss is shown in the figure below. Assume that members EF and CF
are subjected to the highest compressive and tensile forces
when the load P is being
applied.
If the cross sectional area of all members is 2 in
2
, and the allowable axial compressive
stress is 2000psi and the allowable axial tensile stress is 3000psi, calculate:
(a) The maximum force that could be applied
First of all I have to express F
EF
and E
CF
in terms of P
3
4
5
5
CFx
CF
CFy
CF
F
F
F
F
=
=
From Joint F:
E.O.E :
4
5
0
0
5
4
CFy
CF
CF
Fy
F
P
F
P
F
P
Σ
=
⇒
−
=
⇒
=
⇒
=
Tension
3
5
3
3
0
0
5
4
5
4
CFx
EF
CF
EF
EF
EF
Fx
F
F
F
F
P
F
F
P
Σ
=
⇒
+
=
⇒ −
=
⇒ −
=
= −
Compression
Now I can calculate the stresses:
5
5
4
3000
4800
2
8
CF
CF
CF
CF
allowTension
P
F
P
P
lb
A
σ
σ
σ
σ
=
⇒
=
⇒
=
=
=
⇒
=
P

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