1. IPA Researcher, Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899-8611.
2. Senior Research Structural Engineer, Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899-8611 (corresponding author).
3. Professor, Dept. of Civil and Environmental Engineering, Univ. of California, Davis, CA 95616-5270.