8-13. A 7-m long
steel hollow circular tube has an outer diameter of 
and
inner diameter of 
. The tube is pinned at both
ends, and an axial force 
is acting on it. The
modulus of elasticity follows 
. Determine the
distribution of the critical axial buckling load. Also, determine the
probability of failure caused by buckling. Assume that E and P are
independent and Euler’s formula is available.
(Ans. 
, 
)
