ABSTRACT
The idea of principal stress is both conceptually and mathematically more difficult than just adding the axial and bending stresses and keeping the shear stresses separate, but it does give much more information on how a structure acts. As the stresses vary in type and size from point to point of a structure under load, the principal stresses will vary in size and direction from point to point. The idea of the new shear stress shown in is crucial to the understanding of the complex behaviour of beams with non rectangular cross-sections. Often structural elements are made from more than one type of structural material to form composite structural elements. These combinations are made to exploit the different qualities of the materials to produce an element that performs better than one made from only one material. By far the most common form of composite construction for building structures is reinforced concrete.
