1. Professor, Dept. of Civil and Environmental Engineering, Univ. of Michigan, 2028 G.G. Brown Bldg., 2350 Hayward, Ann Arbor, MI 48109 (corresponding author).
2. Lecturer, Dept. of Civil Engineering, Poznan Univ. of Technology, Piotrowo 5, 60-965, Poznan, Poland.
3. Professor, Dept. of Civil Engineering, Poznan Univ. of Technology, Piotrowo 5, 60-965, Poznan, Poland.
4. Research Assistant, Dept. of Civil and Environmental Engineering, Univ. of Michigan, 1024 G.G. Brown Bldg., 2350 Hayward, Ann Arbor, MI 48109.