1. Professor, Dept. of Architecture and Architectural Engineering, Seoul National Univ., Seoul 151-742, Korea (corresponding author).
2. Graduate Student, Dept. of Architecture and Architectural Engineering, Seoul National Univ., Seoul 151-742, Korea.
3. Professor, Dept. of Structural Engineering, Univ. of California, San Diego, CA 92122.
4. Dept. Director, Dept. of Building Structure and Materials Research, Steel Structure Research Division, RIST, Incheon 406-840, Korea.