Study On Tensile Properties Of GFRP Bars Embedded In Concrete Beams Under Sustained Load And Environmental Effects

FRP(Fiber Reinforced Polymer)has been applied widely in pavement engineering,ocean engineering,hydraulic engineering and bridge engineering because to its advantages,such as light weight,high tensile strength,non-corrosive,non-magnetic and excellent fatigue resistance.As a new type of composite material,it's an efficient way to solve the durability problem of reinforced concrete structures that caused by steel corrosion with the replacement of the reinforcement in concrete.However,the most urgent need is to research the long-term mechanical properties for this new materials at present.For that reason,an experimental and theoretical studies on the long-term tensile performance of GFRP bars embedded in actual concrete environment under different corrosion conditions based on the Chinese National Natural Science Foundation-“Degradation mechanism of tensile strength of GFRP bars embedded in concrete beams”(No.51178361)were carried out.Firstly,an experimental investigation on the basic mechanical properties and durability of GFRP bar were carried out respectively.The degradation law of GFRP bars exposed under different corrosion environments was obtained through the analysis of the accelerated aging test data.Combined with microscopic analysis method,the degradation mechanism of GFRP bar exposed in corrosion solution was given.The results show that the degradation mechanism of GFRP bar exposure in an alkaline solution and salt solution was similar.However,the degradation rate of GFRP bars exposure in an alkaline solution was greater than saline solution under the same ambient temperature and exposure time.Secondly,an experimental study on the durability of GFRP reinforced concrete beams under sustained load and severe environments was carried out in order to investigation the degradation law of the tensile properties of GFRP bars in the actual service concrete environment.The influences of the immersion solution,the temperature of environment,sustained loading,working crack and exposure time on tensile strength of GFRP bars were analyzes.Meanwhile,the microstructure of GFRP bar before and after corrosion was surveyed from the micro perspective.Based on these,degradation mechanism of GFRP bars under actual concrete environment wasstudied.Thirdly,based on the accelerated aging and natural aging test data,taking tensile strength as a characterization means,an quantitative analysis of the the relationship between two kinds of environment was conducted by using the grey correlation analysis method.The computing method to calculate accelareted shift factor(ASF)was proposed and accelerated factors between natural aging and accelerated aging were obtained.Finally,the prediction model of long-term tensile strength of GFRP bar embedded in concrete environment was established.On the basis of the accelerated aging data,a half probabilistic reliability prediction model was established based on the Fick's law modified model by introduce the stochastic variable that contain time function,and consider the uncertainty of basic variables.By comparing with the test data amd the model prediction data,to verify the accuracy and practicability of the proposed prediction model.It provides data support and theoretical basis for the tensile strength of GFRP bar embedded in concrete environment prediction and service life forecast.