Megson_StructlStressAnalysis_2nd_solman.pdf

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Structural and Stress
Analysis
Second Edition
by
Dr. T.H.G. Megson
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Solutions Manual
Solutions to Chapter 2 Problems
S.2.1
(a) Vectors representing the 10 and 15 kN forces are drawn to a suitable scale as shown
in Fig. S.2.1. Parallel vectors AC and BC are then drawn to intersect at C. The
resultant is the vector OC which is 21.8 kN at an angle of 23.4 to the 15 kN force.
B
C
10 kN
R
60
°
u
O
15 kN
A
F IGURE S.2.1
(b) From Eq. (2.1) and Fig. S.2.1
R 2 = 15 2 + 10 2 + 2 × 15 × 10 cos 60
which gives
R = 21 . 8kN
Also, from Eq. (2.2)
10 sin 60
15 + 10 cos 60
tan θ =
so that
θ = 23 . 4 .
3
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Solutions Manual
S.2.2
(a) The vectors do not have to be drawn in any particular order. Fig. S.2.2 shows the
vector diagram with the vector representing the 10 kN force drawn first.
12 kN
8kN
u
10 kN
R
20 kN
F IGURE S.2.2
The resultant R is then equal to 8.6 kN and makes an angle of 23.9 to the negative
direction of the 10 kN force.
(b) Resolving forces in the positive x direction
F x = 10 + 8 cos 60 − 12 cos 30 − 20 cos 55 =−7 . 9kN
Then, resolving forces in the positive y direction
F y = 8 cos 30 + 12 cos 60 − 20 cos 35 =−3 . 5kN
The resultant R is given by
R 2 = (−7 . 9) 2 + (−3 . 5) 2
so that
R = 8 . 6kN
Also
tan θ = 3 . 5
7 . 9
which gives
θ = 23 . 9 .
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Solutions to Chapter 2 Problems
5
S.2.3 Initially the forces are resolved into vertical and horizontal components as shown
in Fig. S.2.3.
y
(1.0, 1.6)
x
69.3 kN
30
°
80 kN
40 kN
20.0 kN
(1, 1.25)
R x
50 kN
30
°
35.4 kN
34.6 kN
40 kN
45
°
y
(0, 0.5)
35.4 kN
R y
(1.25, 0.25)
O
x
F IGURE S.2.3
60 kN
Then
R x = 69 . 3 + 35 . 4 − 20 . 0 = 84 . 7kN
Now taking moments about the x axis
R x y = 35 . 4 × 0 . 5 − 20 . 0 × 1 . 25 + 69 . 3 × 1 . 6
which gives
y = 1 . 22 m
Also, from Fig. S.2.3
R y = 60 + 40 + 34 . 6 − 35 . 4 = 99 . 2kN
Now taking moments about the y axis
R y x = 40 . 0 × 1 . 0 + 60 . 0 × 1 . 25 − 34 . 6 × 1 . 0
so that
x = 0 . 81 m
The resultant R is then given by
R 2 = 99 . 2 2 + 84 . 7 2
from which
R = 130 . 4kN
Finally
θ = tan −1 99 . 2
84 . 7 = 49 . 5 .
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