1. Ph.D. Student, Dept. of Civil and Environmental Engineering, Univ. of Michigan, 2350 Hayward, GG Brown Bldg., Ann Arbor, MI 48109 (corresponding author).
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of Michigan, 2350 Hayward, GG Brown Bldg., Ann Arbor, MI 48109.
3. Professor, Dept. of Civil Engineering, Jeju National Univ., Daehakro 66, Jeju-si, Jeju-do, 690-756, Korea.