Theory of structure (TOS)
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In a broad sense, the analysis and design of a structure consists of two parts:

The first part deals with the determination of forces at any point or member of the given structure.

The second part deals with the selection analysis and design of a structure suitable sections to resist these forces so that the stresses and defor­mations developed in the structure due to these forces are within permis­sible limits.

The first part can be termed as “structural analysis” and the second part as “proportioning” or “dimensioning” of members .

Before we can start the analysis, we shall require the entire details of the structure, loading and sectional properties. To proportion a structure, we must first know how it will behave under loading. Therefore, the process of analysis and design of a structure forms an integral part of any design.  In practice, the properties of mem­bers are so chosen as to obtain a specified structure, and then the analysis is carried out. Often the designer may have to readjust his initial dimen­sions in order to get the desired response from the structure. Therefore, the intended purpose of any analysis is to know how the structure responds to a given loading and thereby evaluate the stresses and defor­mations.

The ultimate aim in learning the methods of analysis is, to help design efficient, elegant and economical structures. Analysis helps the designer to chose the right type of sections consistent with economy and safety of the structure. The purpose of structural analysis is to determine the reactions, internal forces, such as axial, shear, bending and torsional, and deformations at any point of a given structure caused by the applied loads and forces.


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