Importance of study of Engineering Mechanics / Strength of materials

Structures (building, bridges, towers etc.,) and their parts are usually subjected to different types of loads such as dead loads, live loads, wind loads, seismic loads, impact loads, etc. The structural elements such as walls, columns, beams, floors, roofs etc. are made up different kinds of materials like steel, reinforced cement concrete, wood, stone, masonry etc. The sizes and shapes of these elements are to be properly designed so that

i.       The elements have the required strength to resist the applied loads (safety)

ii.      The structure and its elemens are stable under the action of external loads (Stability)

iii.     The deformations of elements are within the permissible limits (serviceability)

iv.     The quantities of materials used are as less as possible (economy)

Hence for a good design, a thorough knowledge of physical and engineering properties of all materials used is essential for the designer.

The structural design generally consists of two major steps namely analysis and design. In the process of analysis the most probable loads on the structure are first assessed and the actions such as axial loads, shear force, bending moments, twisting moments etc. developed in the elements are determined. These actions, in turn, develop different type of stresses in the members. In the process of design, suitable sizes are determined for the various members such that stresses developed in them do not exceed the corresponding permissible stresses prescribed for the materials used. This is necessary for the safety of the structure.

It should be also seen that the deformations such as elongation, contraction, deflection, twist etc. do not exceed the maximum permitted values for better serviceability conditions. Anyone of the following two methods is used for designing the structural elements:

1. Finding the exact dimensions required for the member directly from the actions and permissible stresses.
2. Choosing a trial section for the member, determining the actual stresses developed and checking them with the permissible stress values.

Simple members made up of single material may be designed directly by the first method, whereas complex members made up of two or more types of materials and members subjected to combination of different types of stresses are designed by the second method.

Hence, in the analysis and design processes, one should be able to determine the actions at various sections of the elements due to the applied loads and also the stresses and deformations developed in the members due to these actions.