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Section 2
2-51
Allowable Stress Calculation:
Axial Compression:
Critical (KL/r)
y
= 1.0 x 7.07x12/0.795 = 106.73
22
2 2 *29000
126.099
36
c
y
E
C
F
ππ
== =
As (KL/r)
y <
C
c
, the allowable axial stress in compression
()
()
2
2
22
106.73 36
36
1 1 10.89
. . 4 2.12 4 29000
yy
a
FKLrF
F
FS E
ππ
⎡⎤
⎡⎤
⎢⎥
=− =− =
⎢⎥
⎢⎥
⎢⎥
⎣⎦
⎣⎦
ksi
Actual Stress Calculation:
Actual stress (f
a
) = 23.04 /1.938 = 11.88 ksi.
Ratio
11.88
1.09
10.89
a
a
f
F
==
The value calculated by STAAD is 1.09
Member 9, Size L5x5x3/8, L = 5.657 ft., a = 3.61 in
2
From observation Load case 1 will govern, Forces
Fx = 48.44 kip (compression)
Allowable Stress Calculation:
Axial Compression:
Critical (KL/r)
y
= 1.0 x 5.657 x12/0.99 = 68.57