The Experimental Modal Analysis Of City Bridge

Civil engineering structures are important part of national infrastructures that have a direct impact to people's daily life, so it is very necessary to install structural health monitoring system in Bridges, dams and other large civil engineering structures. It is required to understand their dynamic properties during the inspection, assessment and health monitoring of civil engineering structures. Structural modal parameters reflect the dynamic properties, and Structural modal parameter identification is the core of the modal analysis. Structural modal parameter identification can be divided into two categories:traditional and ambient vibration identification techniques. Both in comparison, the modal parameter identification techniques under ambient vibration, which are just based on output data, only need response signal. And there are some other advantages such as without imposing excitations on the structure, save labors and equipment costs, avoid potential damage to the structure, etc. So the modal parameter identification techniques under ambient vibration have been adopted extensively in engineering applications.This paper mainly studies the modal parameter identification techniques under ambient vibration. The main work accomplished as follows:(l)Domestic and international development of bridge health monitoring is reviewed, and its important meaning is discussed. To the problem of the health monitoring technology of bridge structure which involves the structural dynamics as an opportunity, the concept for modal analysis is simply overviewed. And this paper makes a comprehensive of its core question-the modal parameters identification, including the research situation, the existing achievements and existing problems, etc.(2)The paper introduces related principles of the experimental modal analysis focusing on the knowledge of signal processing and modal parameter identification: deduce the formula of DFT and FFT; introduce their respective technical routes of frequency domain and time domain method for the modal parameter identification-, study some methods about the principle, advantages and disadvantages, flow, etc.(3)Systematically elaborate the frequency domain method for the modal parameter identification under ambient vibration. Based on the analysis of the basic system dynamics equation, this paper introduces system modal parameters expression and basic recognition process. The background and formula of peak picking method with unknown input is mainly studied, and its general flow chart is given and problems which are required in the experimental process are discussed. Finally a numerical example is made to verify its validity and feasibility.(4)For further study of peak picking method with unknown input under ambient vibration, an engineering example, Zhengzhou south three-ring flyovers, is applied to verify its stability and applicability. The experimental process is introduced in detail, and the modal parameters of this bridge are indentified with peak picking method. A comparison between the experimental result and finite element calculation results proves the method's feasibility and efficiency.(5)The main works and conclusions of this paper are summarized. The development prospect of large civil engineering structural health monitoring and the further research work of modal parameters identification under ambient vibration are discussed.