1. Professor, Dept. of Civil Engineering, Kunsan National Univ., Gunsan 573-701, Republic of Korea.
2. Professor, Dept. of Civil Engineering, Kunsan National Univ., Gunsan 573-701, Republic of Korea (corresponding author).
3. Graduate Student, Dept. of Civil and Environmental Engineering, Kunsan National Univ., Gunsan 573-701, Republic of Korea.