1. Assistant Professor, Dept. of Civil and Environmental Engineering, School of Engineering, Univ. de Antioquia, Medellín 050010, Colombia (corresponding author).
2. Professor, Dept. of Civil and Environmental Engineering, Northwestern Univ., Evanston, IL 60208.
3. Assistant Professor, Dept. of Civil Engineering, National Univ. of Colombia, Medellín 050041, Colombia.