1. Graduate Student, University of Brasília, Department of Civil and Environmental Engineering, FT, 70910-900 Brasília, DF, Brazil, Telephone: +55 61 3107 0962, Telefax: +55 61 3273 4644, E-mail: ivonnegutierrez@unb.br
2. Professor, University of Brasília, Department of Civil and Environmental Engineering, FT, 70910-900 Brasília, DF, Brazil, Telephone: +55 61 3107 0969, Telefax: +55 61 3273 4644, E-mail: palmeira@unb.br