1. Graduate Student, Dept. of Civil Engineering, National Univ. of Singapore, Kent Ridge, Singapore 119260; presently, Postdoctoral Fellow, Dept. of Civil Engineering, National Univ. of Singapore, Kent Ridge, Singapore 119260. E-mail: duan_wenhui@alumni.nus.edu.sg
2. Professor, Dept. of Engineering Science and Civil Engineering, National Univ. of Singapore, Kent Ridge, Singapore 119260 (corresponding author). E-mail: cvewcm@nus.edu.sg