TABLE OF CONTENTS We are now in a position to calculate internal force distributions in a variety of structural systems, i.e. normal forces, shear forces and bending moments in beams and arches, axial forces in truss members, the tensions in suspension cables and torque distributions in beams. These internal force systems are distributed throughout the cross section of a structural member in the form of stresses. However, although there are four basic types of internal force, there are only two types of stress: one which acts perpendicularly to the cross section of a member and one which acts tangentially. The former is known as a direct stress, the latter as a shear stress.
The distribution of these stresses over the cross section of a structural member depends upon the internal force system at the section and also upon the geometry of the cross section. In some cases, as we shall see later, these distributions are complex, particularly those produced by the bending and shear of unsymmetrical sections. We can, however, examine the nature of each of these stresses by considering simple loading systems acting on structural members whose cross sections have some degree of symmetry. At the same time we shall define the corresponding strains and investigate the relationships between the two.
The simplest form of direct stress system is that produced by an axial load. Suppose that a structural member has a uniform I cross section of area A and is...
