1. Associate Project Scientist, Dept. of Structural Eng., Univ. of California, San Diego, La Jolla, CA 92093-0085.
2. Principal Scientist, CSIR Structural Engineering Research Centre, Chennai, Tamil Nadu 600113, India.
3. Professor, Dept. of Structural Eng., Univ. of California, San Diego, La Jolla, CA 92093-0085 (corresponding author).