1. Professor, Dept. of Civil and Environmental Engineering, Northwestern Univ., Evanston, IL 60208 (corresponding author). E-mail
2. Structural Engineer, GRC Engineering, Inc., 5544 W. 147th St., Tinley Park, IL.
3. Professor Emeritus, Dept. of Civil and Environmental Engineering, Northwestern Univ., Evanston, IL 60208.
4. Research Assistant, Dept. of Civil and Environmental Engineering, Northwestern Univ., Evanston, IL 60208.