> N[1]:=(xi,eta)->(1/2)*(1-xi)*(1-eta)*(1-3*xi-3*eta)*(2-3*xi-3*eta):
> N[2]:=(xi,eta)->(9/2)*xi*(1-xi)*(1-eta)*(2-3*xi-3*eta):
> N[3]:=(xi,eta)->-(9/2)*xi*(1-xi)*(1-eta)*(1-3*xi-3*eta):
> N[4]:=(xi,eta)->-(9/2)*eta*(1-eta)*(1-xi)*(1-3*eta-3*xi):
> N[5]:=(xi,eta)->(9/2)*eta*(1-eta)*(1-xi)*(2-3*eta-3*xi):
> M:=8*G*D*a^2*Int(Int(Phi,xi=0..1),eta=0..1)=8*G*D*a^4*int(int((650/109
> 7)*N[1](xi,eta)+(141130/266571)*N[2](xi,eta)+(95900/266571)*N[3](xi,et
> a)+(95900/266571)*N[4](xi,eta)+(141130/266571)*N[5](xi,eta),xi=0..1),e
> ta=0..1);

                          1    1
                         /    /                             4
                     2  |    |                  199220 G D a
         M := 8 G D a   |    |   Phi dxi deta = -------------
                        |    |                      88857
                       /    /
                         0    0

> M:=evalf(199220/88857)*G*D*a^4;

                                             4
                       M := 2.242029328 G D a

# Der relative Fehler gegenber dem exakten Wert 2.25 von TIMOSCHENKO /
# GOODIER (Tabelle 7.5) betrgt:
> f:=(9/4-199220/88857)/(9/4)=evalf((9/4-199220/88857)/(9/4));

                           2833
                     f := ------ = 0.003542520879
                          799713

> 
