| Fiber reinforced polymer(FRP)has become a new structural material which has been widely used in civil engineering because of its excellent mechanical properties mature fabrication process and strong adaptability and so on.At present,the majority of fiber reinforced composites are still based on thermosetting resin.As thermosetting FRP materials do not have secondary molding performance,the application of thermosetting composites in civil engineering is greatly limited.Thermoplastic FRP materials have been developed rapidly because of their good toughness,heat resistance and the advantages of repeatable or secondary processing,which has become a beneficial supplement to thermosetting FRP materials.However,the resin matrix is a weak link in the high temperature resistance of FRP materials.When the temperature reaches or exceeds the glass transition temperature,the viscosity of the resin increases and the elasticity decreases,which affects the mechanical properties of the FRP material.Therefore,this paper is based on the glass transition temperature of the bonded resin.Based on the experimental research,the basic mechanical properties of thermoplastic epoxy BFRP bars developed by our research group at high temperature and the bond properties between the tendons and concrete are evaluated.On this basis,the feasibility study of thermoplastic FRP reinforced concrete beams is carried out.The mechanical properties at high temperature were evaluated,and the experimental results were compared with those of the existing thermosetting vinyl BFRP bars.The degradation laws of the high-temperature mechanical properties were summarized and analyzed,which provided the basis for the further improvement and application of the mechanical properties.The main research contents and results are as follows:1.Study on basic mechanical properties of thermoplastic FRP bars at room temperature and high temperature.It was found that solvent volatilization had a certain effect on the interlaminar properties of reinforcement through the study of the preparation technology and shear properties of the reinforcement.The tensile properties of BFRP bars at high temperature were tested by local heating method.It was found that the tensile strength and elastic modulus of BFRP bars changed little in the range of resin glass transition temperature,and the tensileproperties of large diameter thermoplastic epoxy BFRP bars were the worst,which were more affected by temperature.2.Study on high temperature bond between thermoplastic FRP bars and concrete.Direct pull-out tests of steel clamps and uniaxial pull-out tests of bonding with concrete were carried out respectively.The results showed that the bonding performance of thermoplastic epoxy BFRP bars was lower than that of thermosetting vinyl BFRP bars,and the influence of temperature was greater.The bond performance between small diameter thermoplastic epoxy BFRP bars and concrete is higher than that of large diameter bars,but the bond properties of thermoplastic epoxy BFRP bars with resin glass transition temperature are almost completely lost.After glass transition temperature,the bond between thermoplastic epoxy BFRP bars and concrete was strengthened,and the bonding properties of thermosetting vinyl BFRP tendons to concrete were almost the same as those at room temperature.3.Study on flexural properties of thermoplastic FRP reinforced concrete beams at high temperature.The thermoplastic BFRP bars are applied to the reinforcement design of concrete beams.Compared with thermosetting vinyl BFRP bars,four-point bending tests of beams are carried out at room temperature and high temperature.The results show that the higher the temperature,the lower the flexural stiffness of the BFRP steel-concrete beams.The crack spacing becomes larger and the decay of thermoplastic epoxy BFRP steel-concrete beam is more serious.After the action of high temperature,the cracks of each beam have great difference,but the others have little difference. |
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