1.1 INTRODUCTION

The study of strength of materials includes the understanding of internal stresses and deformations of members subjected to external loading. It also includes the study of failure criterion applicable for the solids subjected to loads. The major actions on the bodies subjected to external loading can be considered as axial force, which include axial compression and axial tension, shear force, bending moment, and torsion. Often members are subjected to the mentioned actions either individually or in combined state such as combined bending, torsion, and axial thrust. The internal reactions due to the external forces cannot be visualized, whereas the deformations can be observed, thus can be measured. Hence generally, the failure criterion of a body subjected to external loads depends not only on the internal actions but also on the deformations. To quantify the internal actions due to the above-said forces, the action of the forces and the corresponding deformations are to be studied in detail in the subsequent chapters. The different individual actions on members were presented in Figure 1.1(a)–(e). However, in this chapter concept of internal reactions and their effects will be discussed. In the subsequent chapters, the effects of mentioned individual actions and combined actions will be discussed in detail.

1.2 NORMAL STRESS AND SHEAR STRESS

Consider a body subjected to several forces and surface tractions as shown in Figure 1.2. Take a section 1-1, to observe the effect of all forces on the section considered. Let ‘P’ be the net resultant of the forces. The resistance developed by the body to this resultant at any point within the domain of the body is referred as stress.