1. Graduate School of Computational Engineering; TU Darmstadt; Dolivostr. 15 Darmstadt 64293 Germany
2. Institute for Scientific Computing; TU Darmstadt; Mornewegstr. 30 Darmstadt 64293 Germany
3. Institute for Structural Analysis; University of Kassel; Mönchebergstr. 7 Kassel 34109 Germany