1. Former Ph.D. Student, Dept. of Architecture and Architectual Engineering, Seoul National Univ., 1 Gwanak-ro, Gwanak-gu, Seoul 151-744, Republic of Korea.
2. Professor, Dept. of Architecture and Architectural Engineering, Seoul National Univ., 1 Gwanak-ro, Gwanak-gu, Seoul 151-744, Republic of Korea (corresponding author).