1. Assistant Professor, Dept. of Civil Engineering, Texas A&M Univ., 3136 TAMU, College Station, TX 77843-3136 (corresponding author).
2. Research Assistant, Dept. of Civil and Environmental Engineering, Stanford Univ., Stanford, CA 94305-4020.
3. Associate Professor, Dept. of Civil and Environmental Engineering, Stanford Univ., Stanford, CA 94305-4020.