Research In Durability Of Precast Concrete Bridge Piers In Coastal Environment

The precast bridge is one of the important development directions of bridge engineering at present,with obvious advantages such as short construction period,low environmental impact and reliable quality.As the main component that bears the vertical load of bridge superstructure and horizontal load such as earthquake,the mechanical properties and durability of the bridge pier are very important.For the bridges in the coastal environment,the piers are in a high concentration of chloride ion environment,which made them prone to suffer the durability problems such as steel bar corrosion,cover concrete cracking and bearing capacity degradation,which affects their service life.However,the current researches on the durability of bridge piers mainly focuses on cast-in-place concrete piers,and there are relatively few researches on the durability of precast concrete piers.The joint interface and other special characteristics of precast concrete piers which differ from cast-in-place piers may become weak areas of durability.In view of this situation,this thesis selects the precast concrete bridge pier using the connection method of grouting sleeve as the research object,analyzes the effects of different corrosion degrees on the apparent phenomena and mechanical properties of the precast concrete bridge pier specimens,and studies the influence of the joint on the durability of the precast piers in the coastal environment.The main work is summarized as follows:(1)Studies on the mechanism of chloride ion transmission and steel bar corrosion were carried out.Considering that the main durability impact of precast concrete bridge piers in the coastal environment is the corrosion of steel ions caused by chloride ion corrosion,the diffusion,penetration,capillary absorption and electromigration of chloride ions in porous media such as concrete and joint materials were studied.Also,the mechanism of steel bars depassivation and corrosion under the action of chloride ions was analyzed.(2)Electric accelerated corrosion test of the precast concrete bridge pier specimens was conducted.Five precast concrete pier specimens connected with grouted sleeves were designed and immersed in chloride salt solution.According to Faraday’s law,the accelerated acceleration corrosion of the bridge pier specimens was conducted,and the target corrosion degrees were 0%,7.5%,15%,22.5%,and 30%,respectively.The distribution of the corrosive expansion cracks of the pier specimens with changes in corrosion degree were observed and analyzed.The results show that as the degree of corrosion increases,the distribution of corrosive expansion cracks and the width of the cracks increase correspondingly.The main corrosive expansion cracks are mostly distributed at the corresponding positions of the sleeve.The corrosion products adsorbed on the surface of the specimen are concentrated in the corrosive expansion cracks and the bottom joints.(3)The low-cycle repeated loading test study on the specimens of corroded precast concrete bridge piers was carried out.Low-cycle repeated loading was carried out on the test specimens of precast bridge piers with different degrees of corrosion obtained by the electric accelerated corrosion test,and the mechanical properties such as bearing capacity,stiffness,ductility and energy dissipation capacity were used as evaluation indexes to research the influence of corrosion degrees on the durability of the bridge piers.The results of the test found that with the increase of corrosion,the mechanical properties of precast concrete piers decreased significantly,indicating that the durability of precast piers will be greatly reduced when they are continuously corroded during service life.(4)Numerical simulation research in mechanical properties of precast concrete bridge piers were carried out.Based on the Opensees finite element software,the numerical models of the precast concrete bridge pier specimens are established and optimized.Meanwhile,the numerical models are corrected according to the actual corrosion degree of each specimen,and the simulated loading analysis is carried out according to the low-cycle repeated loading test loading method.The numerical simulation results are in good agreement with the test results,especially in terms of bearing capacity,which builds the foundation for the establishment of the bearing capacity degradation model of the precast concrete pier in life cycle.(5)The durability performance of the precast concrete bridge pier in life cycle was evaluated.A probability-based comprehensive evaluation method for durability performance of precast pier was established by using chloride ion diffusion theory,steel bar time-varying corrosion model,corrosion cracking model,bearing capacity degradation model based on Opensees simulation,and path probability model.The method was implemented with actual engineering to conduct analysis on the deterioration of the durability performance in life cycle.