where
It is noted that the in-plane stresses are only linear functions of x3. It then follows, on using (2.210), that all the equilibrium equations (2.120)–(2.122) are satisfied.
It now only remains to determine the value of the displacement component u3 describing the deflection of the beam. From (2.216) and (2.220)
On using (2.215) and (2.222) it can be shown that
so that (2.223) may now be written as
Integration with respect to x3 then leads to
As the shear stresses σ13 and σ23 are everywhere zero, it follows from (2.143), (2.209) and (2.211) that
Integration then yields
These relations must be consistent with (2.226) so that