AbstractThe bridge health monitoring system is being increasingly applied to bridge structure monitoring nowadays. However, due to the limitation in monitoring means and data analysis methods, many deficiencies still exist in the analysis and utilization of the monitoring data of bridge structures. In particular, damage identification and assessment technology is far from reaching the practical stage, and this restricts the development of the overall health monitoring technology. On the basis of the analysis of the strain responses of a bridge under vehicle load by using the theory of bridge strain influence line, we put forward a bridge damage identification and evaluation method based on strain ratio. The stiffness degradation matrix of the structure is deduced using the strain ratio of the corresponding parts of the test and reference sections, and the strain ratio and stiffness degradation matrices are accurately obtained using the load effect of test vehicles under closed traffic conditions. By analyzing a large amount of monitoring data in combination with the theory of random signal analysis and statistical technology, we analyze the probability distribution of the strain ratio and perform damage identification of the test section in accordance with the change in strain ratio distribution. A rapid damage identification method for the test section under closed and open traffic conditions is also proposed. The analysis reveals that the mode of the strain ratio is unchanged when the test section does not experience damage in a certain monitoring period under traffic load. We apply this method to a bridge health monitoring system and adopt Qingyin Yellow River Bridge in Jinan as an example to verify the effectiveness of the method. Results show that the method is efficient, accurate, and universal and can realize rapid and accurate online identification and assessment of bridge damage in closed and normal traffic conditions.