In preceding chapters, two basic problems involving structures were considered: (1) determining the external forces acting on a structure (Chap. 4) and (2) determining the forces which hold together the various members forming a structure (Chap. 6). The problem of determining the internal forces which hold together the various parts of a given member will now be considered.

We will first analyze the internal forces in the members of a frame, such as the crane considered in Secs. 6.1 and 6.10, noting that whereas the internal forces in a straight two-force member can produce only tension or compression in that member, the internal forces in any other type of member usually produce shear and bending as well.

Most of this chapter will be devoted to the analysis of the internal forces in two important types of engineering structures, namely,

1. Beams, which are usually long, straight prismatic members designed to support loads applied at various points along the member.
2. Cables, which are flexible members capable of withstanding only tension, designed to support either concentrated or distributed loads. Cables are used in many engineering applications, such as suspension bridges and transmission lines.