1. Technology Research Institute, Daelim Industrial Co., Ltd., 146-12, Susong-Dong, Jongno-Ku, Seoul 110-732, South Korea.
2. Department of Civil and Environmental Engineering, Kyungsung University, 110, Daeyun-Dong, Nam-Ku, Busan 608-736, South Korea.
3. Department of Civil Engineering, Keimyung University, 1000 Shindang-Dong, Dalseo-Ku, Daegu 704-701, South Korea.
4. Department of Civil Engineering, Seoul National University, San 56-1, Shinlim-Dong, Kwanak-Ku, Seoul 151-742, South Korea.