1. Associate Professor, Dept. of Civil and Environmental Engineering, Univ. of Maryland, College Park, MD 20742; formerly, Lehigh Univ., Bethlehem, PA 18015 (corresponding author). E-mail: zyf@umd.edu
2. Graduate Research Assistant, Dept. of Civil and Environmental Engineering, Lehigh Univ., Bethlehem, PA 18015. E-mail: soz2@lehigh.edu