1. Research Scholar, Dept. of Civil and Environmental Engineering, Vanderbilt Univ., Nashville, TN 37235 (corresponding author).
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of California, Davis, One Shields Ave., Davis, CA 95616.
3. Associate Professor, Dipartimento di Ingegneria Strutturale e Geotecnica, Università Sapienza, 00183 Roma, Italy.