1. Research Fellow, National Center for Research on Earthquake Engineering, 200, Section 3, Xinhai Rd., Taipei 106, Taiwan, ROC (corresponding author).
2. Graduate Student, Dept. of Civil Engineering, National Taiwan Univ., Taipei 10617, Taiwan, ROC.
3. Professor, Dept. of Civil Engineering, National Taiwan Univ., Taipei 10617, Taiwan, ROC.