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# [SOM] Basics of Strength Of Material [Part-3]

## Basics of Strength Of Material continued...Part-3

A member is said to be under pure axial loading when it is subjected to two equal and opposite axial loads in such a way that the magnitude of axial load remains constant throughout the length of the member (ie Axial load =constant, shear force=BM=TM=0).
Pure Bending

A member is said to be under Pure Bending when it is subjected to two equal and opposite couples in a plane along the longitudinal axis of the member (ie Bending couples) in such a way that the magnitude of B.M remains constant throughout the length of the member (ie BM=constant, Axial Load=Shear Force=Twisting Moment=Zero).

Bending Moment

BM at any given cross-section is defined as the algebraic sum of moments either of the LHS of the cross-section or RHS of the cross-section.

Sign Convention For Bending Moment:
Bending Moment at any Cross section is said to be positive: when it is acting in the clockwise direction on the LHS of cross-section or when it is acting in the anticlockwise direction on the RHS of cross-section and vice-versa.

Shear Force
SF at any given cross-section is defined as the algebraic sum of vertical forces either on the LHS of the cross-section or on the RHS of the cross-section.

Sign Convention For Shear Force
SF at a given cross-section is said to be positive: when it is acting in upward direction on LHS of cross-section. Or when it is acting in downward direction on RHS of the cross-section and Vice-versa.

Pure Torsion:
A member is said to be under pure torsion when it is subjected to two equal and opposite couples in a plane perpendicular to the longitudinal axis of the member (ie twisting couple) in a such a way that magnitude of twisting moment remains constant throughout the length of the member (ie TM=Constant, Axial Load=Shear Force= Bending Moment=Zero).

Summary Table of Equivalent Load and their Resultant Effect:

1. 2. 