The Effect Of Freezing And Thawing On The Seismic Fragility Of The Reinforced Concrete Bridge Piers

In cold regions the reinforced concrete structures often suffer from freeze-thaw cycles. Especially concrete of piers of the bridges which located in the water level fluctuating zone is easy to suffer freezing and thawing damage due to the alternation of wetting and drying and the change of temperature, which will affect the performance of the piers. Freeze-thaw resistance is important to durability of concrete structures. Experiencing several freeze-thaw cycles, the mechanical properties of concrete materials and components will degradate, which will effect structure’s fragility. The pier plays an important role in the seismic analysis of bridge structure. This paper mainly studies the change of the fragility under freezing and thawing cycles.In this paper, the main work is as follows:(1) The mass loss rate of concrete, the dynamic elastic modulus of concrete and the complete compressive stress-strain curve of concrete subjected to different freeze-thaw cycles were studied. At the same time, the depth of the concrete cross-section and the height of the pier after freezing and thawing has been established.(2) The moment-curvature relationship of the bridge pier subjected to different freezing and thawing cycles were obtained by using OpenSees. Combining with the constitutive model of concrete suffering freezing and thawing, it can be used to calculate the earthquake damage index of bridge piers.(3) Selecting seismic waves which were consistent with the condition of the ground and input them to the pier simulating model considering the depth and height of the freezing and thawing for the nonlinear time history analysis. Then we can extract the maximum displacement of the top of pier. The fragility of the pier can be analyzed after different freeze-thaw times by using the theory theoretical of fragility curve method. The probability of each type of damage conditions can be obtained under different Seismic intensity. Finally fragility evolution curve of the pier with different freezing thaw cycles can be gotten with the freezing and thawing times in indoor and outdoor. The results show that the seismic fragility will increase with numbers of freezing and thawing.