1. Postdoctoral Research Associate, Dept. of Civil and Environmental Engineering, Virginia Tech, 418 Durham Hall, Blacksburg, VA 24061-0246.
2. Professor, Dept. of Civil and Environmental Engineering, Virginia Tech, 413 Durham Hall Blacksburg, VA 24061-0246 (corresponding author).
3. Associate Professor, Dept. of Civil and Environmental Engineering, Virginia Tech, 409 Durham Hall Blacksburg, VA 24061-0246.