Resultant Moments:

The resultant moments per unit length are defined as

(5.22)

Or these can be written as

(5.23)

Now, using Equation (5.15) we can write,

(5.24)

Now, with the same justification as given for Equation (5.19), we can write the above equation as

(5.25)

This can be written as

(5.26)

where

(5.27)

The matrix  represents the bending stiffness, that is, it relates resultant moments with mid-plane curvatures. Again, the matrix  is also symmetric. Further, it is important to note that the matrix   relates the resultant moments with mid-plane curvatures as well.