1. Postdoctoral Researcher, School of Architecture, Civil, and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland (corresponding author).
2. Postdoctoral Researcher, School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332.
3. Lecturer, Engineering Dept., Univ. of Cambridge, Cambridge CB2 1PZ, U.K.
4. Karen and John Huff School Chair and Professor, School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332.