1. Senior Manager, Daelim Industrial Corp., Seoul 110-732, Korea.
2. Professor, Dept. of Civil and Environmental Engineering, Yonsei Univ., Seoul 120-749 Korea.
3. Graduate Research Assistant, School of Civil and Environmental Engineering, Yonsei Univ., Seoul 120-749, Korea.
4. Associate Professor, School of Civil and Environmental Engineering, Yonsei Univ., Seoul 120-749, Korea (corresponding author).