1. Civil Engineer, Dept. of Highways, Road and Pavement Design Division, Bureau of Materials, Analysis and Inspection, Bangkok, Thailand.
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of Wisconsin, Madison, WI 53706 (corresponding author).
3. Deceased; formerly, Professor, Dept. of Civil and Environmental Engineering, Univ. of Wisconsin, Madison, WI 53706.