1. Marie Curie Postdoctoral Research Fellow, Dept. of Civil, Structural and Environmental Engineering, School of Engineering, Trinity College Dublin, Dublin 2, Ireland.
2. Professor, Dept. of Civil, Structural and Environmental Engineering, School of Engineering, Trinity College Dublin, Dublin 2, Ireland (corresponding author).
3. Associate Professor, Faculty of Civil Engineering and Geosciences, Delft Univ. of Technology, 2628 CN Delft, Netherlands; and Manager, PLAXIS bv, Computerlaan 14, 2628 XK Delft, Netherlands.