Probabilistic Seismic Fragility And Risk Analysis Of Long Span Continuous Rigid Frame Bridge With High Steel Tube-reinforced Concrete Column

The continuous rigid frame bridge becomes the main bridge type across the canyon topography of mountainous area in Western China, because of its advantages of moderate cost, large spanning ability and strong adaptability of terrain. Due to topographical constraints, the piers of continuous rigid frame bridges are higher and higher. However the great weight and poor ductility of reinforced concrete become the bottleneck of the development of the high pier. The steel tube-reinforced concrete column is a new attempt to break the bottleneck. The constitutive model, mechanical properties and failure modes of the steel tube-reinforced concrete column material are quite different from reinforced concrete, which result in the lack of systematic research on its seismic performance and damage assessment. A thorough and systematic study on the seismic performance and damage of steel tube-reinforced concrete column continuous rigid frame bridge with high-pier and long-span has important significance for the design and application of the model bridge structure. The numerical simulation and probability analytic method are used in this paper to study seismic fragility analysis and probabilistic seismic risk of long span continuous rigid frame bridges with high steel tube-reinforced concrete column. The main research contents are as follows:(1) The whole process numerical simulations of eccentric compression failure are carried out on 50 samples with same size and different strength of steel tube-reinforced concrete column by fiber model, and P-M-Φ curves of the sections are obtained. According to the failure states of the sections from the numerical simulations, the failure states of steel tube-reinforced concrete column sections are divided into 4 performance objectives which are respectively "elastic and non-elastic", "in need repair and no need repair", "repairable and non-repairable", and "collapse and non-collapse" states. And 5 damage states-no damage, slight damage, moderate damage, severe damage and complete damage are defined. According to the mapping in P-M-Φ curve of failure strain of different fiber materials, considering the variation of axial force in eccentric compression state, and without considering the uncertainty of the fiber material parameters, the deterministic anti-seismic capacity model of the steel tube-reinforced concrete column section is established based on axial force as variable. At the same time, considering the uncertainty of the fiber material parameters, according to the results of 50 samples from the numerical simulations, the statistic distributions of different damage state curvature index are analyzed, and the probabilistic seismic capacity model of the steel tube-reinforced concrete column section is established based on axial force as variable.(2) A span of 105m+200m+200m+105m long span continuous rigid frame bridge with high steel tube-reinforced concrete column is taken as an example, and 17 seismic waves conform to site characteristics are selected. With PGA as ground motion parameter, and considering P-△ effect, a dynamic elastic-plastic time history analysis is carried out with 17 actual seismic waves and IDA analysis is executed only with one seismic wave. Thus the longitudinal and transverse seismic demand distribution along the height of pier is obtained and the most unfavorable section pier as the control section for the seismic demand analysis is determined. Considering the uncertainty of pier section material parameters and the ground motion, respectively, IDA calculation with 17 seismic waves is carried out. The results of the statistical are analyzed to build up a probabilistic seismic demand model which takes PGA as the variables of steel tube-reinforced concrete column control sections.(3) Using reliability theory, seismic fragility analytic expressions are both deduced when considering uncertainties of structure and ground motion, and only considering uncertainty of seismic ground motion. According to statistic results of the parameters of probabilistic seismic capacity and probabilistic seismic demand, the seismic fragility curves of control sections for steel tube-reinforced concrete column are obtained in the condition of longitudinal and lateral seismic input. Moreover, the different damage law of column and the influence of structural uncertainty on fragility curves are both analyzed. According to the fragility curves of control sections, the exceeding probabilities corresponding different damage of long span continuous rigid frame bridges with high steel tube-reinforced concrete column estimated by the first-order boundary method, and the fragility curves of bridge structure system are obtained.(4) According to the probability model of ground motion parameters, the seismic hazards of different seismic basic intensity area in China are studied. Based on probabilistic seismic fragility analysis results and analytic expression of probabilistic risk function, the probabilistic seismic damage risk and probability seismic demand risk of long span continuous rigid frame bridges with high steel tube-reinforced concrete column are both analyzed, and then the two kinds of risk probabilities are compared. According to the seismic risk analysis results for one year, the seismic risk probability of steel tube-reinforced concrete column and the seismic risk probability of structure system during design reference period are obtained, and based on the present China highway and bridge seismic fortification standards, the seismic performance of long span continuous rigid frame bridges with high steel tube-reinforced concrete column is evaluated.