| A correct finite element model is an important basis for complex response analysis,structural safety assessment and long-term health monitoring of long-span bridges.Therefore,it is very important to establish an accurate and effective baseline finite element model.The baseline finite element model of the long-span hybrid girder cablestayed bridge should be verified by field static and dynamic load tests.It can accurately and fully reflect the true static and dynamic characteristics of the bridge structure in the initial stage.Taking the Chizhou Yangtze River Highway Bridge,a twin-tower asymmetric hybrid girder cable-stayed bridge with a main span of 828 m,as an example,an initial finite element model of the bridge is first established based on the original design drawings.Then such an initial finite element model is calibrated by the results of field loading tests and vibration tests.It is demonstrated that the static and dynamic calculation results of the calibrated model are in good agreement with the measured results.The calibrated finite element model can accurately reflect the true static and dynamic of the Chizhou Yangtze River Highway Bridge before it is opened to traffic.This finite element model can be used as a baseline finite element model for structural safety assessment and long-term health monitoring of the bridge.The main work and conclusions of the thesis are as follows:1.Before opening to traffic,the Chizhou Yangtze River Highway Bridge was inspected for the initial structural state(bridge deck elevation line shape,bridge cable forces),static load tests and dynamic tests,aiming to fully understand the initial state and load behavior of the bridge structure under external loads.At the same time,they are also an important basis for the subsequent establishment of the baseline finite element model.2.The dynamic testing under ambient excitations was carried out to obtain the bridge dynamic characteristics of the Chizhou Yangtze River Highway Bridge.This kind of vibration testing has many advantages such as simplicity,convenience and economy.Peak-picking,frequency domain decomposition and stochastic subspace identification methods are herein implemented to identify the modal parameters of the bridge structure aiming to verify each other.The results show that the fundamental frequency of the Chizhou Yangtze River Highway Bridge is 0.196 Hz where the mode shape of the main beam is first-order transverse bending.The main modal frequencies are concentrated in 0～1.0 Hz.3.The realization method of the initial equilibrium configuration of the long-span cable-stayed bridge in the finite element model is proposed.Namely,the measured bridge deck elevation line is the main control target,while the bridge cable force value is the secondary control target.All subsequent static and dynamic analyses of the cable-stayed bridge should start from this initial equilibrium configuration.4.The geometric nonlinearity of long-span hybrid girder cable-stayed bridge in finite element model is introduced.The results show that the large displacement of the structure has little effect on the static and dynamic analysis results of the bridge structure.Although the linear static and dynamic analysis are sufficient to meet the actual engineering analysis needs,the analysis is always geometrically nonlinear due to cable tensions.5.The space finite element model of the long-span hybrid cable-stayed bridge of Chizhou Yangtze River Highway established in this thesis is in good agreement with the static and dynamic load test results of the real bridge before opening to traffic based on the initial balanced configuration.It shows that the calibrated finite element model is an effective and accurate model,which can be used as the baseline finite element model of the Chizhou Yangtze River Highway Bridge.It can be used as basis for the static and dynamic responses of the bridge under various complex loads,structural safety assessment and bridge health monitoring during service. |
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