1. Ph.D. Student, Dept. of Civil Engineering and Engineering Mechanics, 610 S.W. Mudd Bldg., Columbia Univ., 500 W. 120th Str., New York 10027.
2. Assistant Professor, Dept. of Civil Engineering and Engineering Mechanics, 610 S.W. Mudd Bldg., Columbia Univ., 500 W. 120th St., New York 10027 (corresponding author).
3. Associate Professor, Dept. of Structural Engineering, Univ. of São Paulo, São Carlos, Av. Trabalhador São Carlense, 400, CEP 13566-590, São Carlos, Brazil.