1. Research Assistant, Engineering Research Institute, Seoul National Univ., Kwanak-ro 1, Kwanak-gu, Seoul 151-742, Korea.
2. Professor, Dept. of Architecture and Architectural Engineering, Seoul National Univ., Kwanak-ro 1, Kwanak-gu, Seoul 151-742, Korea.
3. Professor, Dept. of Architecture and Architectural Engineering, Seoul National Univ., Kwanak-ro 1, Kwanak-gu, Seoul 151-742, Korea (corresponding author).
4. Associate Professor, School of Civil and Environmental Engineering, Georgia Institute of Technology, 790 Atlantic Dr., N.W., Atlanta, GA 30332.
5. Ph.D. Student, Dept. of Architecture and Architectural Engineering, Seoul National Univ., Kwanak-ro 1, Kwanak-gu, Seoul 151-742, Korea.