Fragility Analysis Of Railway Long Span Rigid Frame-Continuous Combination System Bridge With High Pier Subjected To Near-Fault Ground Motion

In recent years, with the rapid development of China's transportation network, the western region has emerged a large number of railway traffic lines. In order to cross the place with complex terrain of the western mountains, the railway long span rigid frame-continuous combination beam bridge with high pier has been widely used. Due to the large amount of earthquake belts in the western region as well as the intensive distribution of seismic activity along the railway, the structure and operation safety of railway bridges in the area are facing the potential danger of near-fault ground motion. However, the code for seismic design of highway and railway in China at present does not give a reasonable and effective method for seismic evaluation of the railway long span rigid frame-continuous combination beam bridge with high pier and the influence of near-fault ground motion on seismic behavior of the bridge is also not considered. Therefore, in view of the current inadequate research on the seismic behavior of the railway long span rigid frame-continuous combination beam bridge with high Pier, the seismic vulnerability of the large span bridge with high pier and is systematically studied based on the typical construction of 4 span rigid frame continuous combination beam bridge in the western region of our country. This study mainly completed the work of the following aspects:1. The dissertation summarizes the development course and research status of seismic vulnerability analysis method of bridge on the basis of consulting a large number of literatures, at the same time, the deficiency of the present research is put forward, and the main research contents of the dissertation are introduced.2. The dissertation summarizes the damage indices of bridge structure and the evaluation method of bridge structure damage degree, and then the dissertation investigates the suitable range of various damage indices. Furthermore, the failure criterion of pier flexure failure, shear failure, flexure-shear and bearing deformation have been given in accordance with seismic code and theory of each country. On the basis of this, the dissertation calculates and analyses the damage indices of bridge piers and bearing members and then makes an assessment of bridge seismic damage by taking the 4 span rigid frame continuous combination beam bridge with high pier as an example.3. Research on uncertainty of ground motion is carried out, and the ground motion samples with near-fault characteristics are established. The samples of the bridge model are generated after investigating the uncertainty in the parameters of the bridge model, as a result, the sample database of Ground motion-Railway Bridge with high pier and large span has been established by match both samples. In view of the shortcomings of the three common calculation methods of Fragility Analysis at home and abroad, a method for calculating the vulnerability of bridge based on kernel density estimation is proposed, and the correctness and stability of the method can meet the requirements. In order to find out the best calculation method, this dissertation take the 4 span rigid frame continuous combination beam bridge with high pier as the object, the fragility curves of the components are established by using 4 kinds of vulnerability calculation methods as well as the advantages and disadvantages of various methods are compared. As a result, the seismic vulnerability analysis method is established for the high pier and large span bridges by taking the above research results into consideration. So, the seismic performance of the bridge structure can be evaluated according to the fragility curves which are established by above methods.4. The dissertation has established the bending and shear failure state equation of the railway bridge pier and the state equation of deformation and failure of support by referring to bridge seismic design theory, material failure criterion and bridge seismic damage mechanism method; it has proposed criterion of damage state identification and quantization method for the equation of state; Based on the reliability theory of engineering structure and the method of probability and mathematical statistics, this dissertation has derived a general 3D seismic vulnerability calculation theory of bridge structure which is used to calculate the 3D seismic vulnerability of structure with different state equations. On the basis of this, considering the uncertainty of bridge structure parameters and ground motion, the method of incremental dynamic analysis is introduced to establish the 3D seismic vulnerability analysis method of high pier and large span bridge.5. This dissertation takes the 4 span rigid frame continuous combination beam bridge with high pier as research object, establishing the seismic fragility curves through traditional seismic vulnerability analysis method which corresponds to two damage indices of the damage state equation and the curvature ductility ratio respectively. And the difference between the two kinds of curves is analyzed, which verifies the correctness and applicability of the bridge damage state equation. Based on this, the vulnerability curves of various dangerous components of the bridge are established by the method of 3D seismic vulnerability analysis of railway bridges, and the correctness and feasibility of 3D seismic vulnerability analysis method are verified by comparing the curves with the traditional vulnerability analysis method.6. The dissertation takes the 4 span rigid frame continuous combination beam bridge with high pier as research object, establishing the 3D seismic fragility curve of each risk component through three dimensional seismic vulnerability analysis method for high pier and long span bridges; it has conducted a research on the distribution characteristics of the seismic vulnerability of each risk component of the bridge as well as the influence of different ground motion input direction on the vulnerability of each risk component; The most unfavorable seismic input angle, the quantity and range of seismic vulnerable input angles of each risk component have been studied; The main failure modes of each pier member under three-dimensional earthquake are studied, and the seismic vulnerability of each component is analyzed; The fragility of the bridge system is established based on the first order reliability theory which can be used to assess the general seismic performance of bridge structures under three dimensional near field earthquake.