1. Center for Infrastructure Studies, Univ. of Missouri at Rolla, Rolla, MO 65409-0710; formerly, Dept. of Structural and Transportation Engineering, Univ. of Padova, Via Marzolo 9, 35131 Padova, Italy.
2. Dept. of Structural Engineering, MC-0085, Univ. of California San Diego, La Jolla, CA 92093-0085.
3. Dept. of Structural Engineering, MC-0085, Univ. of California San Diego, La Jolla, CA 92093-0085 (corresponding author).