1. Civil Engineer, Univ. of Brasília, Dept. of Civil and Environmental Engineering, Brasília-DF 70910-900, Brazil.
2. Civil Engineer, Univ. of Brasília, Dept. of Civil and Environmental Engineering, Brasília-DF 70910-900, Brazil.
3. Associate Professor, Univ. of Brasília, Dept. of Civil and Environmental Engineering, Brasília-DF 70910-900, Brazil. (corresponding author).
4. Researcher, Embrapa-Instrumentação Agropecuária, São Carlos-SP 13560-970, Brazil.