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Table 8 Polynomial functions for different boundary conditions and up to two degrees of freedom per Lie algebra element \({\mathbf {Z}}_{I,r}\)

From: Introducing the Logarithmic finite element method: a geometrically exact planar Bernoulli beam element

Boundary cond.

\(\varvec{r}\)

\(\varvec{q}\)

\( \varvec{{\partial ^\mu p_{I,r,q}} (1)}\)

\( {\varvec{p_{I,r,q}} (\alpha )}\)

   

\(\varvec{\mu = 0}\)

\(\varvec{\mu = 1}\)

\(\varvec{\mu = 2}\)

\(\varvec{\bar{q}_J= 0}\)

\(\varvec{\bar{q}_J= 1}\)

\(\varvec{\bar{q}_J= 2}\)

clamped

1

0

\(\bullet \)

\(*\)

\(*\)

\(\alpha ^2\)

\(\alpha ^3\)

\(\alpha ^4\)

 

1

1

\(\circ \)

\(\bullet \)

\(*\)

\(\alpha ^3 - \alpha ^2\)

\(\alpha ^4 - \alpha ^3\)

\(\alpha ^5 - \alpha ^4\)

 

2

0

\(*\) \(^{\mathrm{a}}\)

\(*\)

\(*\)

\(\alpha ^2\)

\(\alpha ^3\)

\(\alpha ^4\)

 

2

1

\(\circ \)

\(\bullet \)

\(*\)

\(\alpha ^3 - \alpha ^2\)

\(\alpha ^4 - \alpha ^3\)

\(\alpha ^5 - \alpha ^4\)

 

2

2

\(\circ \)

\(\circ \)

\(\bullet \)

\(\frac{1}{2} \alpha ^4 - \alpha ^3 + \frac{1}{2} \alpha ^2\)

\(\frac{1}{2} \alpha ^5 - \alpha ^4 + \frac{1}{2} \alpha ^3\)

\(\frac{1}{2} \alpha ^6 - \alpha ^5 + \frac{1}{2} \alpha ^4\)

pin (w/o load)\(^{\mathrm{b}}\)

1

0

\(\bullet \)

\(\circ \)

\(*\)

\(-2\alpha ^3 + 3\alpha ^2\)

\(-3\alpha ^4 + 4\alpha ^3\)

\(-4\alpha ^5 + 5\alpha ^4\)

 

1

1

\(\circ \)

\(\circ \) \(^{\mathrm{c}}\)

\(*\)

(not included in the element formulation)

 

1

2

\(\circ \)

\(\circ \)

\(\bullet \)

\(\frac{1}{2} \alpha ^4 - \alpha ^3 + \frac{1}{2} \alpha ^2\)

\(\frac{1}{2} \alpha ^5 - \alpha ^4 + \frac{1}{2} \alpha ^3\)

\(\frac{1}{2} \alpha ^6 - \alpha ^5 + \frac{1}{2} \alpha ^4\)

 

2

0

\(\bullet \)

\(\circ \)

\(*\)

\(-2\alpha ^3 + 3\alpha ^2\)

\(-3\alpha ^4 + 4\alpha ^3\)

\(-4\alpha ^5 + 5\alpha ^4\)

 

2

1

\(\circ \)

\(\circ \) \(^{\mathrm{c}}\)

\(*\)

(not included in the element formulation)

 

2

2

\(\circ \)

\(\circ \)

\(\bullet \)

\(\frac{1}{2} \alpha ^4 - \alpha ^3 + \frac{1}{2} \alpha ^2\)

\(\frac{1}{2} \alpha ^5 - \alpha ^4 + \frac{1}{2} \alpha ^3\)

\(\frac{1}{2} \alpha ^6 - \alpha ^5 + \frac{1}{2} \alpha ^4\)

pin (moment)

1

0

\(\bullet \)

\(*\)

\(*\)

\(\alpha ^2\)

\(\alpha ^3\)

\(\alpha ^4\)

 

1

1

\(\circ \)

\(\bullet \)

\(*\)

\(\alpha ^3 - \alpha ^2\)

\(\alpha ^4 - \alpha ^3\)

\(\alpha ^5 - \alpha ^4\)

 

2

0

\(\bullet \)

\(*\)

\(*\)

\(\alpha ^2\)

\(\alpha ^3\)

\(\alpha ^4\)

 

2

1

\(\circ \)

\(\bullet \)

\(*\)

\(\alpha ^3 - \alpha ^2\)

\(\alpha ^4 - \alpha ^3\)

\(\alpha ^5 - \alpha ^4\)

pin (distr. load)\(^{\mathrm{d}}\)

1

0

\(\bullet \)

\(*\)

\(*\)

\(\alpha ^2\)

\(\alpha ^3\)

\(\alpha ^4\)

 

1

1

\(\circ \)

\(\bullet \)

\(*\)

\(\alpha ^3 - \alpha ^2\)

\(\alpha ^4 - \alpha ^3\)

\(\alpha ^5 - \alpha ^4\)

 

2

0

\(\bullet \)

\(\circ \)

\(*\)

\(-2\alpha ^3 + 3\alpha ^2\)

\(-3\alpha ^4 + 4\alpha ^3\)

\(-4\alpha ^5 + 5\alpha ^4\)

 

2

1

\(\circ \)

\(\circ \) \(^{\mathrm{c}}\)

\(*\)

(not included in the element formulation)

 

2

2

\(\circ \)

\(\circ \)

\(\bullet \)

\(\frac{1}{2} \alpha ^4 - \alpha ^3 + \frac{1}{2} \alpha ^2\)

\(\frac{1}{2} \alpha ^5 - \alpha ^4 + \frac{1}{2} \alpha ^3\)

\(\frac{1}{2} \alpha ^6 - \alpha ^5 + \frac{1}{2} \alpha ^4\)

  1. Filled circles denote nonzero values, empty circles denote zeros, and asterisks denote arbitrary real numbers. For the meaning of \(\bar{q}_J\), see Section “Full p-refinement and selective p-refinement”. For node I with \(\xi _I = 0\), \(\alpha = 1 - \xi \), whereas for node J, with \(\xi _J = 1\), \(\alpha = \xi \)
  2. \(^\mathrm{a}\) Value of the coefficient associated with this shape function is externally given by the boundary condition
  3. \(^\mathrm{b}\) Simply supported node
  4. \(^\mathrm{c}\) Value is zero due to the local characteristics of the configuration
  5. \(^\mathrm{d}\) Distributed load in transversal direction in the neighborhood of the position of the node on the neutral axis