1. Research Fellow, Dept. of Civil and Environmental Engineering, National Univ. of Singapore, Kent Ridge, Singapore 119260 (corresponding author).
2. Professor, Engineering Science Programme and Dept. of Civil and Environmental Engineering, National Univ. of Singapore, Kent Ridge, Singapore 119260.
3. Professor, Univ. Européenne de Bretagne, Univ. of South Brittany, Laboratoire d'Ingénierie des Matériaux de Bretagne, Centre de Recherche, Rue de Saint Maudé, BP92116 56321 Lorient Cedex, France.