Can't integrate function



hello to all,

i Would like to know why maxima doesn't integrate the following function.

Thanks for your help

a0:2/T*integrate(vi(t),t,-T/2,T/2);

vi(t):=VAaux(t)+vb(t);

VAaux(t):=if t<-T/2 then VAaux(t+T) elseif t<T/2 then va(t) else VAaux(t-T);

vb(t):=1/4*cos(15*%pi*t)-1/8*sin(30*%pi*t);