This paper presents a comparative study to identify damage in bridge structures based on the modal flexibility matrices. In the study, the classical Pandey and Biswas method and the Ritz vectors extracted from flexibility matrix are considered. By utilizing a new idea for load dis-tribution vector, the new aspects of the Ritz vectors are presented. In the approach the mode shapes, are substituted for spatial load distribution vector. The abilities of the methods are demonstrated using experimental modal data of four damage levels of a plate girder from I-40 Bridge over the Rio Grande, with a coarse mesh of sensors. The influence of number of vibration modes on damage patterns are studied. The results show that the localization resolu-tion declines by the classical flexibility based method in the early stages of damage. The pre-dictions based on the Ritz vectors are found to closely match to the actual response of the bridge. Two first vibration modes are very influential on the damage pattern and incorporat-ing data from the additional modes are not found to improve the localization performance.

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