Study On Static And Dynamic Test Technology And Condition Assessment Of Continuous Box Girder Bridge

With the development of the traffic and the speeding up of the pace of urbanization, bridge becomes even more important in the increasingly busy roads and city traffic. A lot of new type bridges, large span wide bridge, as well as super-wide bridges have emerged one after another, various forms of bridge sections have been used, among which, box-section is one of the forms frequently used. Box-section beam is a closed thin-walled structure, its length is much larger than cross-sectional size, and its wall thickness is far less than the width or height of section. As a result of thin-walled box having a good structure and mechanical behavior, and suiting for the cantilever assembly and cantilever casting modern construction, so it has been widely used in the bridge project.Due to the advances of automation technology as well as the general applications of computer, testing technique and analysis means have got considerable progress and can provide accurate and reliable test data, so testing has got a more important status in the research, design and construction of bridge, is still an important means to resolve new issue in the field of bridge engineering, and has been paid more attention by bridge workers.Practice has proved that objective, accurate and timely detection on the bridge project is an important technology means to ensure the quality of the bridge project, and one of indispensable steps of construction acceptance, as well as an important tool to identify the extent and causes of the disease of bridge.As a result, research in the static and dynamic testing technology of continuous box girder bridge, and condition assessment based on the measured static and dynamic parameters of the bridge structure is very necessary.As the complexity of the box girder's mechanical, its research methods are varied, but it can be divided into two categories by summary, namely, analytical and numerical methods. In the analytical method, the calculation theoretical research of box girder is focused on the analysis of torsion, distortion and lateral deflection.With the increasingly widespread application of computer, in addition to analytical method, numerical analysis method is becoming an important way to analysis thin-walled member. Among them, by the above-mentioned analysis method come from the development of the finite element method, or stiffness method; also numerical methods derived from the basic theory of the finite element; the use of mature shell finite element analysis software for the thin-walled analysis is real commonly used in the project. In addition, finite strip method and finite bar element method are also commonly used in numerical methods for the thin-walled member. Currently, numerical solution methods are using various finite element software mainly based on finite element method, finite strip method and finite bar element method, to analysis the mechanical characteristics of the box girder structure, among them, grillage method is most popular.The theory research methods of box girder shear lag are mainly: Kaman theory, elasticity theory solution method, analogy-bar method, energy variational method, numerical analysis method and etc. Elastic theory solution method including the theory of orthotropic plate, folded plate theory, shell theory and etc. Numerical analysis methods are mainly the finite element method, finite strip method and finite segment method. Currently, among the theory methods of shear lag research, energy variational method and numerical analysis methods are most popular.Currently, the dynamic analysis of box girder is mainly finite element method, and the analytic method is still rare. Folded plate theory is an analytical method used to solve the thin-walled box girder structure. It has been successfully applied to the static analysis of structure.First, on the basis of deeply analysis of the mechanical characteristics of continuous box girder bridge, this article based on the theories of solid finite element method, space grillage method, vibration analysis and etc, established the static and dynamic model of a continuous box girder bridge, and calculated the theoretical value of the bridge structure in the test load.Then made a research on the static test technology for continuous box girder bridge, the research are main about: the needed static parameters of the bridge, selecting a reasonable sensor and acquisition system, how to determine the loading location of the bridge structure and so on; Further more, made a research on dynamic test technology for the continuous box girder bridge, the research are main about: the excitation method for the continuous box girder bridge , the layout of dynamic measuring point, the extraction of dynamic parameters and so on, then analyzed condition assessment of bridge based on the measured static and dynamic parameters. Finally, made static and dynamic test on the first joint four-span prestressed concrete box girder bridge of the overpass crossing Beijing-Harbin railway was on-site, and made an condition assessment of this bridge based on the measured static and dynamic parameters .This paper mainly studied the following:(1) On the basis of mechanical characteristics of the continuous box girder bridge, studied establishment method of grillage model and solid finite element model.(2) Calculated the static parameters of the bridge structure based on grillage model, took this as a theory guider to study the static parameters needed to be captured for the bridge, selecting reasonable sensor and acquisition system, and how to determine the loading location of the bridge and so on. Took measurements of the static parameters of the bridge structure, and assessed the stiffness and strength of the bridge structure based on the measured static parameters.(3) Calculated the shear lag effect of the bridge structure based on the solid finite element model, and compared the measured shear lag effect with the theoretical value, made a preliminary study on the shear lag effect of continuous box girder bridge.(4) Made an in-situ dynamic test on four-span prestressed concrete box girder bridge, sampled the random response of dynamic measuring points under ambient excitation, analyze the structure of the bridge Dynamic parameters (mode, the natural frequencies, damping ratio) by using the random reduction technology and eigen-system realization algorithm, evaluated the overall performance of the bridge structures based on the measured dynamic parameters.