1. Dept. of Civil and Environmental Engineering, Univ. of Michigan, 2105 GG Brown, Ann Arbor, MI, US, e-mail: junxing@umich.edu
2. Dept. of Civil and Environmental Engineering, Univ. of Michigan, 2032 GG Brown, Ann Arbor, MI, US, (Corresponding author), e-mail: romanh@umich.edu