1. Research Professor, Dept. of Civil and Environmental Engineering, Hanyang Univ., Seoul, 133-791, KR, e-mail: banhoki@hanyang.ac.kr
2. Ph.D. Student, Dept. of Civil Engineering, 362D Whittier Research Center, Univ. of Nebraska, Lincoln, NE 68588, US, e-mail: pravatko@huskers.unl.edu
3. Associate Professor, Dept. of Civil Engineering, 362N Whittier Research Center, Univ. of Nebraska, Lincoln, NE 68583, US (Corresponding author), e-mail: ykim3@unl.edu