1. Assistant Research Professor, Dept. of Civil and Environmental Engineering, Dankook Univ., Yongin 448-701, Korea.
2. Professor, Dept. of Civil and Environmental Engineering, Myongji Univ., Yongin 449-728, Korea (corresponding author)
3. Ph.D. Candidate, Dept. of Civil and Environmental Engineering, Myongji Univ., Yongin 449-728, Korea.
4. Assistant Professor, Dept. of Civil and Environmental Engineering, Dankook Univ., Yongin 448-701, Korea. E-mail: Dongsu-