1. Professor, Dept. of Civil Engineering, The Univ. of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-8656, Japan (corresponding author). E-mail: fujino@civil.t.u-tokyo.ac.jp
2. Lecturer, Faculty of Civil Engineering, Ho Chi Minh City Univ. of Technology, Ho Chi Minh City, Vietnam; formerly, Postdoctoral Research Fellow, The Univ. of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-8656, Japan. E-mail: nam@bridge.t.u-tokyo.ac.jp