1. Assistant Professor, Dept. of Civil Engineering, UbonRatchathani University, Thailand, 34190. E-mail: griengsak@ubu.ac.th
2. Associate Professor, The Univ. of Texas at Austin, Dept. of Civil, Architectural and Environmental Engineering, 1 University Station C1748, Austin, TX 78712 (corresponding author). E-mail: ewilliamson@mail.utexas.edu