1. Doctoral candidate, Dept. of Structural and Geotechnical Engineering, Univ. of Rome “La Sapienza,” Via Eudossiana 18, Rome 00184, Italy.
2. Research Structural Engineer, Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899-8611 (corresponding author).
3. NIST Fellow, Building and Fire Research Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899-8611.