Research On Combination Value Of Dispersion Coefficient And Seismic Performance Index Of Continuous Girder Bridges In High-speed Rail

Bridge is an important part of the high-speed rail, whose damage state is closely related to economic losses and life safety. The lessons learned from seismic hazard that have occurred recently has led to the conclusion that performance-based seismic design theory is recognized step by step and is used in the seismic theory analysis and practice of bridge. However, the research on improving the target performance level of bridges and achieving a group of anticipated performance objectives under different design earthquake levels is very little and the research results is not completed. Considering the properties of railway bridge piers with large section and low ratio of reinforcement, common three-span continuous girder bridges are selected to conduct the incremental dynamic analysis. The main contents are as follows:(1) The combination value of dispersion coefficient βcom in the fragility curve is an important parameter for evaluating the seismic performance of bridges. The definition of the variability is based on the empirical method both in China and foreign countries. Based on the summarization of the calculation method of βcom, according to the characteristics of the girder bridges in high-speed rail, the influential factors on βcom such as the pier height, the span and the reinforcement ratio of pier are analyzed and discussed by constructing the finite element models of the corresponding girder bridges. Incremental Dynamic Analysis (IDA) method is applied to analyze the influence of these factors excited by selected fifteen earthquake records. The calculation of βcom can be used as the reference value for evaluating the seismic performance of the continuous girder bridges in high-speed rail.(2) According to the failure characteristics of bridge piers and the need of performance-based seismic design in High-speed Rail, the strain of steel and concrete is used as the criterion of bridge pier damage and three-level performance objective parameters are given. Twelve kinds of continuous girder bridges are selected for the study, and the influence of pier height, span and reinforcement ratio on drift ratio and damage index DI is analyzed. IDA results in 15 earthquake records are studied by using statistical method, and the drift ratio and damage index limit value are put forward with a guaranteed rate of 95% which correspond to three performance level. The drift ratio and damage index limit value are compared with that in the provisions among New Zealand standard, Japan design code, and American design code, and the results show that the indices for three designated performance levels are reasonable.(3)The elastic-plastic analysis model considering seating’s nonlinear mechanical behavior because of failure is established in this paper, in which seating’s mechanical behavior is simulated based on its damage state. The influence of bearing failure on seismic performance of bridge is studied by using nonlinear time history analysis. According to the study, fixed seatings have a greater proportion of failure state in rare earthquake, which leads to large displacement, but it can decrease the response of fixed pier because of slap of seatings. It can be concluded that seating is vulnerable component, but its damage can protect substructure of bridge. After the failure of fixed seatings, the pounding between continuous girder bridge and adjacent simply supported bridge is likely to happen. The pounding effect of bridges is influenced tremendously by gap size of superstructure segments, which includes maximum pounding force and collision times. The collision is more likely to occur when the gap size is small, and the force is relatively large. The collision restrains seatings’displacement but it has little impact on piers.