ABSTRACT
A rod is a long solid, generated by moving a plane cross section along the normal line passing through the centroid, called the rod axis. Rods may have a constant or a variable cross section; the axis may be straight or curved. A straight rod having a constant cross section is usually called a bar. Rods are used as structural elements given various names according to the configuration of loading. The problems of elastic rods are generally three-dimensional problems. Consider a long rod having a straight axis and a cross section that is either constant or varying gradually with no abrupt changes. The rod is acted upon by a system of forces in equilibrium with some constraints on displacement. It is instructive to derive from elementary equilibrium considerations the equation of the elastic curve in bending, which will be referred to in forthcoming sections dealing with displacements, buckling, and beams on an elastic foundation.
