In this paper we discuss the existence of positive solutions of the fully fourth-order boundary value problem
which models a statically elastic beam fixed at the left and freed at the right, and it is called cantilever beam in mechanics, where is continuous. Some inequality conditions on f guaranteeing the existence of positive solutions are presented. Our conditions allow that is superlinear or sublinear growth on . For the superlinear case, a Nagumo-type condition is presented to restrict the growth of f on x2 and x3. Our discussion is based on the fixed point index theory in cones.