Research On The Stress-Strain Relationship Of FRP Confined Concrete With Initial Stress

Fiber Reinforced Polymer has been widely used in underground engineering, bridge engineering and construction projects, due to its light weight, corrosion resistance, high strength, easy construction, fatigue resistance, and other advantages. At present, there have been a number of studies on the uses of FRP confined concrete column, but these studies didn’t consider effect of initial load. In actual engineering, FRP was usually applied to the existing reinforced concrete structures. Before wrapping FRP, concrete columns had to bear a certain amount of initial stress. Then concrete has produced lateral expansion, so that the concrete column confined by FRP has existed secondary load, such that there has a certain Strain hysteresis of FRP. These will affect the constraints capacity of FRP confined concrete column. In view of this situation, this paper has conducted a study about FRP confined concrete with initial load, as follows:(1) On the basis of the existing peak stress, peak strain calculation model, combined with initial stress test results, compared and analysis the difference of the existing model with the experimental results. Then there had a parameter analysis of FRP confined concrete calculation model, such as the level of initial stress, lateral restraint stiffness, lateral restraint strength. Peak stress and peak strain model with initial stress was established by introducing the initial stress level affecting factors, and compared with the test data.(2) Based on the existing stress-strain curve model of FRP confined concrete column, a stress-strain curve model of FRP confined concrete column has been established by combining characteristic of stress-strain curve of FRP confined concrete column with initial stress and introduction of a new peak stress and peak strain model Introducing a new peak stress and peak strain calculation model, and been compared with the test data.(3) First considering the case of the initial stress, axial stress-strain curves for actively confined concrete, lateral-axial strain model and calculation method of FRP tensile strain at failure have been put forward. Then, based on the actively confined model of Mander et al., an analysis-oriented model of FRP confined concrete column with the initial stress has been established by using incremental iterative method. By comparison with the experimental data, the analysis-oriented model was been in good agreement with experimental data, and can be a good predictor to the stress-strain relationship of FRP confined concrete column with initial stress. Finally, by analyzing the different initial stress level, the strength of concrete and FRP layers, this paper found that, with increasing levels of initial stress, the peak stress and peak strain will be weakened, and the higher initial stress level, the greater the impact on them; With the increasing strength of concrete, the stress-strain curve of the overall rise and peak stress will increase, while declining to shift the peak strain; With the improvement of the number of layers of FRP axial stress will continue to increase, and the peak stress and peak strain will be greatly improved.