1. Graduate Research Assistant, Dept. of Civil Engineering, Univ. of Nebraska-Lincoln, 2200 Vine St., 362E Whittier Research Center, Lincoln, NE 68583.
2. Assistant Professor, Dept. of Civil Engineering, Univ. of Nebraska-Lincoln, 2200 Vine St., 362P Whittier Research Center, Lincoln, NE 68583 (corresponding author).