| Structural health monitoring technology has been made considerable headway in ensuring the safety of building, bridges, dams and many other infrastructures. Among them, the rapid development of bridge construction in our country, bridge health monitoring technology has become the important means in China owing to the active construction of large scale bridges. Over the long-term service of bridges, they will be affected by many factors such as external environment erosion. Its loss of pre-stress and increase of deflection will have adverse effect on the safety of bridge operation, which are potential dangers in bridge construction and maintenance of bridge safety. Monitoring the loss of pre-stress and increase of deflection of bridge has become increasingly significant in the bridge monitoring. Traditional measurement techniques have defects, which are characterized by "point" sensing and could only measure a few preset points in practical engineering.Bridge structures mainly adopt box girder structure. Aiming at the characteristics of box girder structure, this study uses the theoretical analysis, numerical simulation and experiments to study the monitoring method using distributed and long range sensors. The research are described as follows:1. This paper first studys the shear lag effect and shear deformation mechanism in the box girder and monitoring the impact of the method. This paper argues that the irregular of strain distribution caused by shear lag effect can be well considered during the strain collection. Shear deformation in the box girder should not be neglected in different situations. The ratio of shear deformation to total deformation are provided. The general case of tendons used in practice also need to be considered to the shear lag effect of the whole structure, which reflects on the shear lag coefficient values.2. This study expands the monitoring method based on the distributed long-gauge strain. The monitoring of box girder pre-stress method is proposed using distributed strain and shear lag, which allows distributed fiber sensors to be used in monitoring the pre-stress. The results prove that the method has better applicability according to different reinforcement method. The best monitoring position advice has been given at the same time by finite element method.3. On the basis of the elementary beam theory, the effect of shear lag, shear deformation and pre-stress on the box girder deflection has been studied, which uses energy principle and timoshenko beam theory. Shear lag coefficient is introducted to improve the conjugate beam method. The method is not affected by loadings, which has an advantage in theory. At the same time, this paper suggests a simplified formula by using correction coefficient in engineering application.4.For the sake of verifying the effectiveness of monitoring system mentioned in section 2,3; concrete scale models are constructed. The longitudinal strain under different pre-stress and vertical load are monitored by distributed fiber sensors and strain gages. Results of pre-stress monitoring show that the maximum error is about 5%-10%. The monitoring precision of strain gages is slightly better than that of FBG sensors at about 1%-5%. Results of deflection monitoring show that the maximum error is within 10%.There is no significant difference between two types of sensors. By using simplified formula and correction coefficient, the monitoring error is within 10%, which makes it easily used in engineering. Experiment results prove that using distributed long gauge sensors has feasibility in practical engineering health monitoring. |
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