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For the beams that are made of a material that resists differently
tensile and compression (white and gray cast iron, hardened tool
steel, some bronze, concrete, etc.) it is advantageous to use
asymmetric cross-sections with respect to the neutral axis. In this
case, the condition of strength in the largest normal stress has the
form

M y 
 t  z max t    ;
x max t 
J 
z
 (6.23)
M y 
 c  z max c   

x max , c 
J
z 
where y and y – the distance from the neutral axis to the most
t c
distant points in the stretched and compressed section areas;

  and   – allowable stress in tensile and compression.

t c
The most rational use of the material will be when,


 t    , and  c    ; it is necessary to
x max t x max c

y  
t  t , (6.24)
y  

c c
i.e., the distance from the most distant points in the stretched and
compressed sectional areas to the neutral axis should be
proportional to the corresponding allowable stresses.

6.6 Beams of rational cross-section

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