Page 63 - 4560

P

  max    . (5.24)
 F
With stability conditions (5.24) we can solve the problem of three
types.
1. Checking the stability is to check the condition of stability
(5.24) as follows:
– determine the minimum moment of inertia of the cross
section of the rod and the minimum radius of inertia (with the
same consolidation in the main planes):

i  J F ;
min min
– calculate the flexibility of the rod by the formula (5.17);
– on the tables a reduction factor of basic allowable stress  is
chosen;
– substitute extracted raw data in the stability condition (5.24)
to test its performance.
2. Determination of allowable loads on stability conditions
is done in the same way, except for the last step, instead of it
calculate allowable load:
  P    F . (5.25)

3. Selection of the cross-section of the rod, or projecting
calculation is based on calculating the cross section area in
stability conditions:
P
F  . (5.26)
 
 
This problem has no unique solution, since the inequality (5.26)
consists of two unknown quantities: the cross-sectional area
F and the ratio  , which depends on undefined yet cross section
size, its shape and length of the rod. So, the problem is solved by
successive approximations with testing intermediate results using
the stability conditions as follows:
– take arbitrary value of coefficient  1=0,5…0,6 and calculate
the square F 1 of rod cross section:

63