Bridge condition and safety based on measured vibration level

Along the years, there were efforts by researchers in quantifying structural performance and damage in function of vibration measurements. Curves proposed by several authors try to relate acceleration spectrum to damage level, which was determined based on experimental survey accomplished on buildings. The present work investigates a vibration based criteria for bridge structures as a basis to evaluate damage and performance in existing bridges and also to be used for long-term performance at the time of bridge design. With this purpose, it was analyzed a data base of Brazilian bridges which were structurally identified and had their dynamic effects measured during traffic flow. For the damage evaluation, a damage index based on the change of the dynamic properties and the general condition of these structures observed during a detailed inspection were taken into account. After that, damage indexes were related to measured vibration too. The results show a clear correlation between the damage index and the fatigue reliability index with the intensity of bridge vibration. As a final result, from the observed correlations, limits of acceleration are proposed to be considered in existing and newly designed bridges to certify a correct long-term condition and safety to fatigue effects. A critical approach of current Brazilian Standard (NBR-15307 2005) which suggests damage estimation in function of bridge vibration index is also carried out.