| The mechanical properties of the existing concrete structure will degrade to a certain extent after high temperature（fire）,which will lead to potential safety hazards in the subsequent service period of the structure.How to quickly evaluate and repair some seriously damaged concrete components after fire has become a hot issue in engineering field.In recent years,fiber reinforced polymer（FRP）reinforcement has been widely used in engineering due to its characteristics of rapid repair and corrosion resistance.Using FRP to strengthen damaged concrete structures has the potential advantage of rapidly restoring the bearing capacity as before.Considering that the research on the axial compression behavior of FRP-confined concrete after heated is limited at present,this paper mainly studied the axial compression behavior of carbon reinforced polymer（CFRP）-confined concrete after heated under different heating temperatures,different FRP layers and different cooling methods.The mainly completed works list as follow:（1）Based on the microscopic analysis（XRD,SEM,thermogravimetry analysis and differential thermal analysis）and optical microscope observation,the surface damage of concrete and the physical and chemical changes of the internal components of concrete after high temperature were analyzed.（2）52 concrete specimens（including 4 contrast specimens）treated with different cooling methods after heated were carried out based on the axial compression test.The effects of different heating temperatures,different CFRP layers and different cooling methods on the axial compression behavior of CFRP-confined concrete after heated were studied.（3）The applicability of Zhu model,Khan model,Lie model and Li and Guo model for calculating ultimate strength of concrete after heated is verified.The results show that the calculated values of Khan model and Zhu model are in good agreement with the experimental values.Based on the results above,the applicability of khan-Teng and Zhu-Teng combined models for calculating peak strength of concrete subjected to CFRP-confined concrete after heated is further verified.The calculated values of Zhu-Teng model are in good agreement with the experimental values.（4）With the increase of the heating temperature,the stress-strain relationship of CFRP-confined concrete after heated gradually deviates from the characteristics of bilinear strengthening curve.Based on the test results,the applicability of Lam and Teng model and Yang and Feng model to determine the stress-strain relationship of CFRP-confined concrete after heated is verified.The results show that the calculated curves of Yang and Feng model are in good agreement with the experimental curves in the temperature range from 20℃ to 400℃.When the temperature exceeds 400℃,Yang and Feng model is no longer applicable.When the temperature exceeds 700℃,a linear model is recommended to predict the stress-strain relationship. |
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