An incompletely documented bridge 09-125-16 in Cass County, ND was tested by Bridge Diagnostics, Inc. (BDI). A Grillage numerical model is created with their field data to simulate the bridge responses due to traffic loads. A validated bridge model matching the field test data is developed. Based on the validated numerical model, loading of the corresponding bridge under different damage scenarios is performed to capture the change of displacement mode shapes. Using the difference of these displacement mode shape data, a modified curvature method is suggested for identifying damage in bridges, which is shown successfully through the modeling results of bridges with fictitious damages. An in-lab experiment of a steel plate without damage under impact forces is adopted to produce vibration data. The modified curvature is then computed using the experimental mode shape data and its change is found to correlate very well as anticipated by the suggested theory.