1. Professor, Dept. of Civil Engineering, Santa Maria Univ., Casilla 110-V, Valparaiso, Chile (corresponding author).
2. Lecturer, Dept. of Civil Engineering, Santa Maria Univ., Casilla 110-V, Valparaiso, Chile.
3. Assistant Professor, Dept. of Civil Engineering, Santa Maria Univ., Casilla 110-V, Valparaiso, Chile.
4. Professor, Chair of Engineering Mechanics, Univ. of Innsbruck, Technikerstr. 13, A-6020, Innsbruck, Austria.