1. Ph.D. Candidate, School of Civil, Environmental and Architectural Engineering, Korea Univ., 145, Anam-ro, Sungbuk-gu, Seoul 136-713, Korea.
2. Engineer, Dept. of Tunnel Engineering, Dongmyeong Engineering, Consultant, and Architecture, 501, Cheonggyecheon-ro, Dongdaemun-gu, Seoul 130-823, Korea.
3. Professor, School of Civil, Environmental and Architectural Engineering, Korea Univ., 145, Anam-ro, Sungbuk-gu, Seoul 136-713, Korea (corresponding author).