1. McCormick Institute Professor and W.P. Murphy Professor of Civil and Mechanical Engineering and Materials Science, Northwestern Univ., Evanston, IL 60208 (corresponding author).
2. Graduate Research Assistant, Northwestern Univ., Evanston, IL 60208.
3. Professor, Department of Mechanics, Faculty of Civil Engineering, Czech Technical Univ. in Prague, Thákurova 7, 166 29 Prague 6, Czech Republic