Any type of structural material can be classified as elastic, plastic, and rigid materials. When subjected to external loading, elastic materials undergo deformation. However, the elastic deformation vanishes when the loads are removed. Materials which undergo continuous deformation when loaded are called plastic materials. The plastic deformation can be considered as permanent deformation. The plastic materials do not regain their original dimensions when the loading is removed. Materials which do not undergo any deformation when loaded are called rigid materials. Structural members are always designed such that they do not exceed the elastic condition under working loads. Shearing deformation is caused by shearing forces. A structure is regarded as the assembly of a number of components, such as walls, beams, slabs, columns, foundations, etc., that stay in balance. A spring can be characterized as an elastic member, whose primary role is to distort or deflect the load applied.