1. Dept. of Civil and Environmental Engineering, Univ. of Wisconsin, Madison, WI 53706 (corresponding author).
2. Dept. of Civil Engineering, National Taiwan Univ., Taipei 10617, Taiwan.
3. Dept. of Civil and Environmental Engineering, Louisiana State Univ., Baton Rouge, LA 70803.
4. Dept. of Civil Engineering, Texas A&M Univ., College Station, TX 77843.