The Finite Element Method - Mechanics of Structures: Variational and Computational Methods - page 414

FIGURE 6.43
A four-sided element.

only the interpolation functions associated with these nodes. For example, if only node 6
is present in addition to the basic four corner nodes, the element shape functions are

1
4 (

1
4 (

1
2 N 6

N 1 = 1 − η)( 1 − ξ) , N 2 = 1 + ξ)( 1 − η) −

1
4 (

1
2 N 6 ,

1
4 (

N 3 = 1 + η)( 1 + ξ) − = 1 − ξ)( 1 + η) , (6.148)

4

1
4 (

2

N 6 = 1 − η )( 1 + ξ)