1. Assistant Professor, Dept. of Civil Engineering and Engineering Mechanics, Univ. of Arizona, 1209 E. 2nd St., Tucson, AZ 85721. E-mail: gduan@email.arizona.edu
2. Associate Professor, Dept. of Civil and Environmental Engineering, Michigan Tech Univ., Houghton, MI 49931. E-mail: barkdoll@mtu.edu