1. Postgraduate Researcher, Dept. of Structural Engineering, Univ. of California at San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0085.
2. Graduate Student, Dept. of Structural Engineering, Univ. of California at San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0085.
3. Professor, Dept. of Structural Engineering, Univ. of California at San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0085 (corresponding author).