1. Graduate Student, Dept. of Architecture and Architectural Engineering, Seoul National Univ., 1 Gwanak-ro, Seoul 151-744, Korea.
2. Senior Researcher, Building Structure Research Group, POSCO Global R&D Center, 100 Songdogwahak-ro, Incheon 406-840, Korea (corresponding author).
3. Professor, Dept. of Architecture and Architectural Engineering, Seoul National Univ., 1 Gwanak-ro, Seoul 151-744, Korea.