1. Assistant Professor, Civil and Environmental Engineering, Rutgers, State Univ. of New Jersey, 96 Frelinghuysen Rd., Piscataway, NJ 08854.
2. Professor, Civil and Environmental Engineering, Virginia Tech, 418 Durham Hall, Blacksburg, VA 24061-0246.
3. Professor, Civil and Environmental Engineering, Virginia Tech, 750 Drillfield, Blacksburg, VA 24061-0105 (corresponding author).