1. Manager, ENG Center, Samsung C&T, HongWoo Annex Bldg. 7F 1327-1, Seocho-Gu, Seoul, 137-858 Korea.
2. Assistant Professor, Zachry Dept. of Civil Engineering, Texas A&M Univ., College Station, TX 77843-3136 (corresponding author).
3. Professor, School of Civil, Environmental and Architectural Engineering, Korea Univ., Seoul, 136-713 Korea.