Health Monitoring And Condition Assessment Based On Rotating Angle For Bridge Structure

In recent years, it is happened frequently that the damages of bridges even the collapse accidents of bridge structures. In order to ensure the safe operation of the in-service bridges, it is of great significance to carry out health monitoring for bridges. Although the study of bridge structure health monitoring technology has undergone decades of development, research of the inclinometer method based on rotation angle measurement technology which is a new way for bridge structural health monitoring is very inadequate still. Therefore, based on the rotation angle data obtained from inclinometers, the further application in deflection measurement and bearing capacity evaluation is discussed in this article. Moreover, this paper also studies the application of rotation mode theory in structural modal parameters identification, damage identification and dynamic deflection calculation based on rotation angle responds. Specifically, the main contents of this paper are as follows:(1) After an extensive literature research, this paper summarizes various common existing techniques of bridge deflection measurement and the advantages and disadvantages of each method is analyzed as well. On this basis and the combination of bridge deformation theory, an indirect method of deflection measurement —Inclinometer Method is introduced. And then, this paper focuses on various deflection fitting methods based on rotation angle data, including single span fitting method based on least squares principle, cubic spline interpolation, rational cubic spline interpolation and integration method and so forth. Through the finite element software ANS YS, response of a simply supported beam and a continuous beam under both static load and moving load is simulated. Subsequently, this paper analyzes and compares the precision and computing speed of these algorithms as well as the corresponding arrangement of the measuring points. Besides, an indoor experiment of the simply supported and continuous beam is conducted. As a result, the validity of these fitting method is proved by the measured rotation angle and deflection data.(2) According to the modal analysis theory, this thesis summarizes the principles and methods of the existing four kinds of modes:displacement mode, strain mode, curvature mode and long-gauge macro strain mode. On this basis, the modal model of rotation angle response is established according the vibration differential equation of the continuum. The formula of rotation-frequency response function and the orthogonality of rotation mode is also given. Furthermore, this paper introduces the damage identification method based on rotation modal analysis theory, including the modal curvature method, finite difference method of the rotation mode and long-gauge macro strain mode. The provement uses ANSYS numerical analysis and the response of the simply supported beam and the continuous beam is obtained. The spectrum analysis method is applied to identify the rotation modal parameter and the application of rotation mode in damage identification is also studied through presetting damage in the structure.(3) Through the finite element software ANSYS, rotation responses of a simply supported beam and a continuous beam under random load is simulated. Moreover, the application of rotation modal matrix method in structural dynamic displacement calculation is studied. Through the simulative results, it is found that high precise dynamic displacement result can be obtained by the first three order modal matrix and theoretically proved that the rotation modal matrix method can be applied to monitor structural dynamic deflection.(4) This paper also introduces the basic methods of bearing capacity evaluation for old bridges briefly and gives the method of choosing coefficient Z2 coefficient that based on load test Using the displacement obtained from the Inclinometer Method, evaluation of a simply supported beam's bearing capacity is carried out in laboratory.