1. Assistant Professor, Dept. of Civil Engineering, Hanyang Univ., 17 Haengdang-dong, Seongdong-gu, Seoul 133-791, Korea (corresponding author). E-mail: jseo@hanyang.ac.kr
2. Senior Researcher, Korea Highway Corporation, 430 Geomto-Dong, Sujeong-Gu, Seongnam, Kyungki, Korea. E-mail: padre@hanyang.ac.kr