1. Professor, Dept. of Civil Engineering, Federal Univ. of Rio Grande do Sul, 90035-190, Porto Alegre, Brazil (corresponding author).
2. Ph.D. Student, Dept. of Civil Engineering, Federal Univ. of Rio Grande do Sul, 90035-190, Porto Alegre, Brazil.
3. Dept. of Civil Engineering, Federal Univ. of Rio Grande do Sul, 90035-190, Porto Alegre, Brazil.
4. Associate Professor, Dept. of Civil Engineering, National Univ. of Asuncion, San Lorenzo 2160, Paraguay; formerly, Ph.D. Student, Dept. of Civil Engineering, Federal Univ. of Rio Grande do Sul, 90035-190, Porto Alegre, Brazil.