1. Senior Researcher, Korea Institute of Construction Technology, 2311 Daehwa-Dong, Ilsan-Gu, Goyang-Si, Gyeonggi-Do 411-712, South Korea.
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, 205 N. Mathews Ave., Urbana, IL 61801.