1. Dept. of Structural Engineering, Norwegian Univ. of Science and Technology, Trondheim, 7491 NO.
2. Dept. of Structural Engineering, Norwegian Univ. of Science and Technology, Trondheim, 7491 NO (Corresponding author), e-mail: ya.peng@ntnu.no
3. SINTEF BYGGFORSK, Trondheim, 7491 NO.
4. Norwegian Public Roads Administration (NPRA), Bergen, 5845 NO.