| From invention to application all over the world, reinforced concrete materials have been developed more than one hundred years. Concrete and steel, which are the two main components of that, also have a great development and a huge change. The research on the reinforced materials in our country, compared to developed countries, slightly lags behind. In the Code for design of concrete structures (2010 edition), the bar with yield strength of 400MPa and 500 MPa has become the main type of reinforcement. The steel with strength level of 600 MPa has just been developed and been able to apply to the practical projects. On one hand, the development and popularization of high strength steel is the trend of The Times, and the premise of the application is to have clear understanding of the performance of high strength steel. On the other hand, the concrete structure has damaged from time to time under the cyclic load in earthquake disasters which have occured frequently these years. The performance of the longitudinal steels under cyclic loads is also worthy of attention.After the large-scale use of reinforced concrete structures for a long time, it is found that the durability of such structures is not so perfect as imagining. In the long-term service, with the effect of some corrosive medium, corrosion in reinforced concrete is inevitable. The changes of mechanical properties of corroded steel bar have been investigated by numbers of domestic and foreign scholars. But these studies mainly focus on mono tonic tensile or repeated loading, researches on the capacity of bearing cyclic loading are very limited. In recent years, earthquake disasters have occurred frequently. Changes in the performance of old concrete structures and the RC structures with durability degradation problem induced by corrosive medium under earthquake, are problems in urgent need to being understood. This paper focuses on the two of both aspects.(1) This paper reviews the history of the development of reinforcement steel model, summarizes the most classic model in each stage, and discusses the improvements and shortcomings of these models. In consideration of the characteristics of the reinforcement in the earthquake, the low-cycle fatigue model of the steel bar under cyclic loading is discussed. And the possibility of introducing the corrosion factor into the model of this kind is also discussed.(2) A series of monotonic loading and variable amplitude cyclic loading tests of HRB400, HRB500 and HRB600 grade steel bars were carried out by using a self-modified steel bar test machine. The mechanical properties of the specimens under monotonic compression, which were in different slenserness ratioes, were investigated. The stress characteristics and the load capacity variation of the longitudinal steel are discussed, when the nonstraint length of the steel changes. The applicability of the existing compression buckling models to the HRB400 steels in China has been verified. In the cyclic loading tests, the seismic performance and failure characteristics of different grades of steel, with different slenserness ratioes, are compared. The performance and test data of the new HRB500 and HRB600, which are not fully used, is provided. The applicability of the existing reinforcement hysteretic model considering the buckling to the HRB400 grade bar in our country is verified.(3) The steel bars in the concrete slabs were accelerated into corrosion by a lab method using the direct current supplied through a voltage stabilized power, with external coating wet salty sands. And a number of steel bars with different diameter and different corrosion levels were prepared. The corrosive characteristics of these steel bars were similar to those corroded under the environment with chloride ions in actual construction projects. The feasibility and reasonableness of using this method to obtain corroded steel bars in research were verified.(4) A series of low cycle fatigue tests were carried out to investigate the seismic behavior of corroded steel bars obtained by lab methods. The test data and phenomena were obtained. In addition, based on the test data, this paper makes a statistical analysis, successfully introduces the influence of the corrosion into the existing fatigue life model of steel bar, and establishes a new model of the fatigue life of the corroded steel bar. The model is in good agreement with the experimental data.(5) To study the reinforced concrete members in the environment with chlorine ions. The existing corrosion development model and the mechanical properties model of corroded steel bars are combined. After predicting the corrosion degree of reinforced concrete structure in coastal areas, the seismic performance of reinforced concrete columns is analyzed by OPENSEES. The simulation is in order to provide a reference for evaluating the mechanical properties of this kind of structures used in the long term.(6) The nonlinear dynamic time history analysis is carried out using incremental dynamic analysis method on reinforced concrete piers. And on the basis of this, the structural vulnerability analysis is carried out. The seismic response and failure probability of the pier column before and after the reinforcement getting corroded are analyzed. The effect of corrosion on the seismic performance of reinforced concrete piers is recognized more clearly, and the theoretical basis for the seismic performance evaluation of the steel corroded bridge piers is provided. |
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