Research On Durability Of Bolt Anchor Structure Based On Multiple Coupling Factors

With the process of reform and opening up, the process of urbanization in China, and especially the ―One Belt And One Road‖ strategy, bolt anchor structure achieves unprecedented wide range of development in the construction of Civil and Hydraulic Engineering. Their speed of development, large-scale applications, and the application volume has ranked first in the world. But the work environments for bolt anchor structure are very harmful, and there are some widespread corrosive media, stray currents and stress. Simultaneously, bolt anchor structures will suffer serious stress corrosion when they are under loads. Bolt anchor structures in such environment will gradually age, damage or even fail. There are many engineering accidents due to the lack of durability caused by the failure of anchorage around the world, which are considered as time bombs by some scholars. Obviously, research on durability of bolt anchor structures is significant and urgent.Many researchers in the world carry out a large number of theoretical and experimental studies on concrete structures and the durability problems faced. But their work is mainly limited to the reinforced concrete structures. The work environment, stress state of reinforced concrete structures are different from those of bolt anchor structures, therefore the research results of the reinforced concrete structures cannot be applied directly to the bolt anchor structures. Thus the study on the durability of bolt anchor structures is significant. However, research in this field is still in the foundation stage. There is a lot of work to do in experimental models, testing methods, data analysis, combination of the experimental results and the data of the practical project evaluation system, etc.Durability of anchoring structures is impacted with many factors in soil and rock environment, and these factors influence each other, showing a strong randomness and fuzziness. The article analyzes the erosion degenerate mechanism on bolt anchor structures subjected to multiple coupling conditions; and also conducts some researches on the durability factors of bolt anchor structures under serveral corrosive media and stress complex conditions. Meanwhile, the article combines AHP and fuzzy mathematic theory and assesses the durability of bolt anchor structures via FCE. The specific works and results in this paper are summarized as follows:A new anchor specimen corresponding with pratical stress state is designed, and a new approach to test durability of bolt anchor structure considering multiple coupling factors is established. Anchor specimens under single corrosive medium and the composite corrosive medium with long-term immersion, drying-immersion cycles and load are tested. Corrosion damage mechanism of bolt anchor system under complex factors are studied via analysis of experimental results, which support the corrosive media law of anchor structure under multiple coupling factors.(2) The diffusion process of the corrosive media inside the bolt anchor structure was studied using the thermal theory. The simulation result of the software PFC2 D were compared to that calculated form the theory formula, and the feasibility of using the PFC2 D to model the diffusion process of the corrosive media was verified. This paper carried out the simulation of the diffusion process of single corrosive solution, the composite corrosive solution under the complex conditions of long-term immersion method, dip bake cycle method, and the long-term load. The simulation result were compared and verified by the experiment data.(3) The development of the micro cracks under the long term stress were studied using the micro fracture mechanism theory. This paper develops the time-effect coefficients of the bolt anchor structure under long term stress using the chemical reaction rate theory and knowledge of crack growth kinetics. Also in this work how to calculate the decrease the diameter of the parallel bond with time, and how to estimate the failure time is introduced. In this paper, the stress corrosion and cracking of the bolt anchor structure was simulated and compared to the experiment results.(4)The impact of the chemical corrosion on the stress corrosion was studied. Experiment results show that the diffusion of the corrosive media into the concrete will cause chemical reaction, produce insoluble mineral salts, swelling and cracking, resulting in deterioration of the concrete anchor, accelerating the stress corrosion. This effect was simulated using the thermal module and the mechanic module of PFC2 D software. The ion concentration was calculated by the thermal module. Then these information are read by the mechanical modular, and the critical strength for the crack opening was modified using the ion concentration, in order to model the crack opening process. The result using this approach is more close to the experiment than only considering the stress corrosion.(5)A new ―Thermal- Micromechanics coupling approach‖ was developed to calculate the diffusion of corrosive media in the bolt anchor structure. The simulation uses the thermal module and the mechanic module simultaneously. The thermal module outputs the chloride ion concentration distribution, and the mechanical module modify the stress corrosion result using the information of the ion concentration distribution. On the other hand, the mechanical module outputs the information of the stress and crack in the model, which will be used by the thermal module to modify the boundary of thermal calculation and generate the ―thermal crack‖. By comparison with experimental data, this coupling calculation approach is proved to be sufficient to simulate corrosion and crack process of the bolt anchor structure under corrosive environment and long term stress better.(6)Uncertain factors about erosive ion in anchor body and reinforcement are analysed, and a new semi-analytical probabilistic forecasting model based on FOSM is established. This model is used in some specimen where the anchor system gets to a certain probalility and leads to a corrosion destruction or reinforcement erodes to fail. Compared with the traditional deterministic parsing model, this new model throws light on the failure probability about sensitivity of every factor in anchor system, and it can analyse the influence on mean value and coefficient of differentiation of these factors.(7) Factors and features of durability of anchor structure are comprehensively studied, and a new approach about evaluating durability of anchor sturucture is estabilished.A series of researches about durability of bolt anchor structures under multiple coupling conditions via experiments and therotical analysis are completed. These achievements provide some ideas and methods for the further research.