1. Ph.D. Candidate, Dept. of Structural Engineering, Univ. of California at San Diego, 9500 Gilman Dr., MC 0085, La Jolla, CA 92093-0085 (corresponding author).
2. Professor, Dept. of Structural Engineering, Univ. of California at San Diego, 9500 Gilman Dr., MC 0085, La Jolla, CA 92093-0085.
3. Ph.D. Student, Dept. of Civil, Chemical, Environmental and Materials Engineering, Univ. of Bologna, Viale Risorgimento 2, 40136 Bologna, Italy.
4. Civil Engineer, V. Vagna 48, 65022 Bussi sul Trino (PE), Italy.