1. Assistant Professor, Dept. of Civil Engineering, National Univ. of Singapore, Block E1A, #07-03, 1 Engineering Dr. 2, Singapore 117576, Singapore; formerly, Dept. of Civil and Environmental Engineering, 473 Via Ortega, Room 126, Y2E2 Building, Stanford Univ., Stanford, CA 94305 (corresponding author).
2. Associate Professor, Dept. of Civil and Environmental Engineering, 473 Via Ortega, Room 257, Y2E2 Building, Stanford Univ., Stanford, CA 94305.