1. Professor and Holder of the Buchanan Chair, Zachry Dept. of Civil Engineering, Texas A&M Univ., College Station, TX 77843.
2. Associate Professor, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, Urbana, IL 61801.
3. Ph.D. Candidate, Zachry Dept. of Civil Engineering, Texas A&M Univ., College Station, TX 77843 (corresponding author).