ABSTRACT
At the end of this chapter, you should be able to:
• define second moment of area and radius of gyration • derive second moments of area of regular sections – rectangle, triangle, circle and semicircle • state the parallel and perpendicular axis theorems • determine second moment of area and radius of gyration of regular sections using a table of derived results • determine second moment of area and radius of gyration of composite areas using a table of derived results
The first moment of area about a fixed axis of a lamina of area A, perpendicular distance y from the centroid of the lamina is defined as Ay cubic units. The second moment of area of the same lamina as above is given by Ay2, i.e. the perpendicular distance from the centroid of the area to the fixed axis is squared. Secondmoments of areas are usually denoted by I and have limits of mm4, cm4, and so on.
