  The aim of this paper is to study the following fourth-order operator:
  T[p,c]\,u(t)\equiv u^{(4)}(t)-p\,u"(t)+c(t)\,u(t)\,,\quad t\in I\equiv
[a,b]\,, coupled with the non-homogeneous simply supported beam boundary
conditions: u(a)=u(b)=0\,,\quad u"(a)=d_1\leq0\,,\ u"(b)=d_2\leq 0\,.
  First, we prove a result which makes an equivalence between the strongly
inverse positive (negative) character of this operator with the previously
introduced boundary conditions and with the homogeneous boundary conditions,
given by: T[p,c]\,u(t)=h(t)(\geq0)\,, u(a)=u(b)=u"(a)=u"(b)=0\,, Once that we
have done that, we prove several results where the strongly inverse positive
(negative) character of $T[p,c]$ it is ensured. Finally, there are shown a
couple of result which say that under the hypothesis that $h>0$, we can affirm
that the problem for the homogeneous boundary conditions has a unique constant
sign solution.
