1. Full Professor, Dept. of Civil and Environmental Engineering, Univ. of Brasilia, 70910-900 Brasilia, Federal District, Brazil (corresponding author).
2. Ph.D. Student, Dept. of Civil and Environmental Engineering, Univ. of Brasilia, 70910-900 Brasilia, Federal District, Brazil.
3. Associate Professor, Dept. of Mechanical Engineering, Univ. of Brasilia, 70910-900 Brasilia, Federal District, Brazil.
4. Full Professor, Dept. of Mathematics, Univ. of Ciego de Ávila, 65100 Ciego de Ávila, Carretera Morón Km 9.5, Cuba.