________________________________________________________________________
PROBLEM (11.63) Determine the smallest allowable diameter d of a steel rod which may
be used to support an axial load P = 40 kips for Le = 12 ft.
Given: E = 29 x 106 psi, σy = 36 ksi
SOLUTION
244Ad rIAd
π
===, 26
3
2 (29 10 ) 126.1
36 10
c
C
π
×
==
×
Assume 12 144 .
e
Lft==in ec
Lr C>
and use Eq. (11.25):
26
2
(29 10 )
1.92( )
all e
P
ALr
π
σ
×
== ; 32 6
22
40 10 (29 10 )
4 1.92(144 4 )dd
π
π
××
=×
from which
2
433
1.92(160)(144 4)
(29 10 )
d
π
×
=×, di3.26 .n
=
Slenderness ratio is
144 176.7 126.1
3.26 4
e
L
r==>
Our assumption was correct and
3.26 .di=n
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