1. Professor, Dept. of Civil Engineering, Univ. of New Mexico, MSC 01 1070, Albuquerque, NM 87131-0001 (corresponding author).
2. Graduate Research Assistant, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, 1611 Titan Dr., Rantoul, IL 61866; formerly, Graduate Research Assistant, Dept. of Civil Engineering, Univ. of New Mexico, MSC 01-1070, Albuquerque, NM 87131-0001.