1. Assistant Professor, Dept. de Ingeniería Civil, Univ. del Bío-Bío, Avenida Collao 1202, Concepción, Chile (corresponding author).
2. Associate Professor, Dept. of Civil and Coastal Engineering, Univ. of Florida, 460-C Weil Hall, Gainesville, FL.
3. Lecturer, Dept. of Civil and Environmental Engineering, Univ. of Auckland, Private Bag 92019, Auckland Mail Centre, Auckland 1142, New Zealand.