1. Research Assistant, Institute of Structural Mechanics, Bauhaus-Univ. Weimar, Marienstrasse 15, 99423 Weimar, Germany.
2. Research Assistant, Dept. of Civil Engineering, Division of Structural Mechanics, Katholieke Univ. Leuven, Kasteelpark Arenberg 40, B-3100 Heverlee, Belgium.
3. Professor, Dept. of Civil Engineering, Division of Structural Mechanics, Katholieke Univ. Leuven, Kasteelpark Arenberg 40, B-3100 Heverlee, Belgium.