1. Associate Professor, Dept. of Civil Engineering, Federal Univ. of Rio Grande do Sul, Porto Alegre, Brazil (corresponding author).
2. Ph.D. Student, Dept. of Civil Engineering, Federal Univ. of Rio Grande do Sul, Porto Alegre, Brazil.
3. Associate Professor, Faculty of Engineering and Architecture, Univ. of Passo Fundo, Passo Fundo, Brazil.
4. Research Fellow, Dept. of Civil Engineering, Federal Univ. of Rio Grande do Sul, Porto Alegre, Brazil.