1. Postdoctoral Fellow, Bundesanstalt für Materialforschung und –prüfung (Federal Institute for Materials Research and Testing), 12205 Berlin, Germany (corresponding author).
2. Frank M. Taylor Professor, Dept. of Civil and Environmental Engineering, Univ. of Maine, Orono, ME 04469.
3. Professor, Dept. of Civil and Environmental Engineering, Tufts Univ., Medford, MA 02155.