1. Ph.D. Candidate, Dept. of Civil Engineering and Engineering Mechanics, Columbia Univ., 610 S.W. Mudd Bldg., 500 W. 120th St., New York, NY 10027.
2. Associate Professor, Dept. of Civil Engineering and Engineering Mechanics, Columbia Univ., 610 S.W. Mudd Bldg., 500 W. 120th St., New York, NY 10027 (corresponding author).
3. L. B. Ryon Endowed Chair in Engineering, Dept. of Civil and Mechanical Engineering, Rice Univ., Houston, TX 77251.