The Identification Study Of A Bottom-through Concrete-filled Steel Tube Truss Arch Bridge Base On The Operational Modal

With the economy development of China, the functions of bridges are becoming more and more important. They are the guarantee of the economy’s rapid development, the throat of transportation, the top priority of the national security. Thus the security and durability of the bridges have become the focus of the public attention. It’s necessary to know well the conditions of bridges by detection methods in time to avoid some serious accidents. The identification of bridge modal parameters can know more about the health of bridges effectively. The modal parameter identification methods include the traditional modal parameter identification and operational modal parameter identification. Since the traditional one has many shortcomings, the operational one is widely used. Operational modal parameter identification is under the state of real operation of structures. It has higher accuracy and becomes more coincident with the actual conditions of structures. Because the operational modal parameter identification is influenced by many factors and its theories are complex, so this thesis lays some certain foundations of the health detection of bridges which is based on the operational modal parameters identification methods of a Bottom-through Concrete-filled Steel Tube Truss Arch Bridge. The work and achievements of the thesis are as follows:(1) It makes a brief introduction of the accidents and security vulnerabilities of bridges both in China and foreign countries. The significance meaning of the bridges’ health detection and its development status is also stated. Through the structural vibration theory, knowledge about the modal analysis will be talked. Finally this thesis focuses on the research situation, pre-existing achievements and existing problems of the modal parameters identification.(2) As the signal processing is rather important, some knowledge of it will be introduced including signal types, Fourier analysis and Joint Time-Frequency Analysis. And then the PP, Frequency Domain Decomposition, Admittance Circle in the frequency domain; the LSCE, Time series method, random decrement technique, NExT, Stochastic subspace identification method in the time domain are introduced through the theories, advantages, disadvantages and the recognition of frame diagram.(3) By means of the basic modal analysis theories, the thesis introduces systematically the related expressions of the structure modal parameter and its basic identifying process. The key point is the discussion of the Orthogonal Polynomial Curve-fitting Method upon the structure modal parameter identification in the operational modal. With its theory analysis and equation derivation, the advantages and disadvantages of this method are detailed explained.(4) In the operational modal, take the impact load that the vehicles influence on the bridges to be the shock excitation origin, then use the Locomotive Measure Point Method to collect the operational acceleration and combine with t the Orthogonal Polynomial Curve-fitting Method to conduct a modal experiment with a Bottom-through Concrete-filled Steel Tube Truss Arch Bridge. And identify the mode of vibration, frequency and damping ratio of the bridge at last. Analyze the reasons of the production of errors by the test data comparison of the122m bridge spans and the62m ones.