Damage Diagnosis of Bridge Girders via Modal Flexibility Deflections, Inertia Force vectors, and strain energies

This paper presents a new method for identifying damage in bridge girders based on modal flexibility deflections. By utilizing modal inertia forces for spatial load distribution vector, a new approach for obtaining modal flexibility deflections is presented. By flexibility deflections due to the modal inertia forces, a new two-stage damage identification method is pro-posed for beam-like structures. In damage severity estimations, the concepts of static beam deflections are utilized. The abilities of the proposed method are demonstrated using experimental modal data of the two full-scale bridge girders. Four damage scenarios of a steel plate girder from I-40 Bridge over the Rio Grande river and the surface damages in a pre-stressed concrete box girder removed from Provincial Highway Bridge over the Qu'Appelle river are considered and discussed. The influence of uniform load surface and the number of vibration modes on damage patterns are studied. The results show that the localization resolution declines between 15%-30% when applying the uniform load surface method, and the two first vibration modes are very influential on the damage patterns. In most cases, the predictions based on the flexibility deflections due to the modal inertia forces are found to closely (above 90%) match to the actual damage of the bridge girders. Finally, the performance of the pro-posed method in the presence of modelling errors and noisy data is investigated. The results indicate that the proposed method is efficient in damage identification of beam-like structures.