1. Associate Research Fellow, Korea Research Institute for Human Settlements, 254 Simin-daero, Dongan-gu, Anyang-si, Gyeonggi-do 431-712, South Korea (corresponding author).
2. Associate Professor, Dept. of Civil and Environmental Engineering, Virginia Tech, Virginia Polytechnic Institute and State Univ., 900N. Glebe Rd., Arlington, VA 22303.