1. Assistant Professor, Dept. of Civil Engineering, National Univ. of Singapore, Singapore 117576. E-mail: cvemq@nus.edu.sg
2. Research Scholar, Dept. of Civil Engineering, National Univ. of Singapore, Singapore 117576. E-mail: g0403653@nus.edu.sg
3. Associate Professor, Dept. of Civil Engineering, Univ. of Texas at El Paso, El Paso, TX 79912. E-mail: rcheu@utep.edu