Studies On The Damage Identification Of Reinforced Concrete Girder Bridges

With the development of the transportation, bridge health monitoring has become a hot research topic, in which damage identification is a key problem. In this dissertation, the damage identification of simple supported or continuous reinforced concrete (RC) girder bridges caused by overloading is studied through theoretical analysis, numerical simulation and experimental analysis. The main works and achievements are as follows:(1) The frequently used dynamic fingerprints are summarized and their sensitivities are analyzed for the damage identification of RC girder bridges.βindex andηindex based on flexibility matrix are proposed to detect damage position, and the feasibility of the proposed process is proved with numerical simulation.(2) To identify the damage degree, an improved direct stiffness determination (IDSD) method, together with a sectional service-state evaluation method, is proposed. The accuracy of proposed IDSD method is proved by the comparison with the results of existing direct stiffness determination method and finite element (FE) analysis. Two RC beams with a span of 7m are tested and their damage degrees are assessed with the proposed service-state evaluation method which is based on IDSD method.(3) For damage identification caused by overloading, the relationship between modal force area and Normalized Load Level index is established. The historical maximal load identification method is proposed which is based on the modal force and FE simulation. This method is successfully applied in two 7m RC beam experiments to assess the different load levels.(4) Based on the above works, the damage detection procedure of RC girder bridges is proposed. A continuous rigid frame concrete model bridge, which has 3 spans and a total length of 18m, is implemented in this work. Four load cases and ten different load steps are tested to simulate the vehicle load and different levels of overloading. After every load step, dynamic properties of the bridge are tested, and damage detection procedure is used to identify the damage of the model bridge. The results show that the proposed procedure in this dissertation is able to identify the damage position and damage degree effectively on every load step.(5) In order to detect the damages located at the position where the displacement mode is unsensitive, CFRP alarm sensors and prestressed CFRP alarm sensors are developed. Test results show that CFRP alarm sensors have alarm abilities when the concrete cracks and the steel reinforcements yield. Prestressed CFRP alarm sensors are more sensitive in the low strain region, as they are able to reduce the strain when the resistance abrupt change.