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Figure 6.8

It must be remembered that the formula (6.11) is deduced for
the case of pure bending. However, the condition
l  5 ,
h
where l – the length of the beam ( in the multispan beam –
length of span), and h – the height of the cross-section, the
formula (6.11) can be used in direct shear bending. In calculating

the ratio l  5 of the beams more accurate formulas of elasticity
h
should be used.

6.4 Determination of tangential stresses

 
Recall (see. p. 1.7) that the shear force Q x that occurs in the
y
plane of the cross-section of the beam is resultant of elementary
tangential forces dF :
y
Q   x   y  dF .
y
F
According to the law of parity of tangential stresses there are

tangential stresses in longitudinal section planes     .
x y
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