1. Professor, Dept. of Civil Engineering, Federal Univ. of Rio Grande do Sul, Porto Alegre 90040-060, Brazil (corresponding author).
2. Postdoctoral Researcher, Dept. of Civil Engineering, Federal Univ. of Rio Grande do Sul, Porto Alegre 90040-060, Brazil.
3. Lecturer, Faculty of Engineering and Architecture, Univ. of Passo Fundo, São José, Brazil.
4. Senior Lecturer, Dept. of Civil Engineering, Federal Univ. of Rio Grande do Sul, Porto Alegre 90040-060, Brazil.