Experimental Study On Tensile Property Of FRP Bars And Bond Behavior Between FRP Bars And Concrete After High Temperature

Fiber Reinforced Polymer (FRP) bars has the following advantages:light weight, high tensile strength, corrosion resistance and so on. FRP bars can be used in reinforcing concrete structure instead of steel bars or as a supplementary reinforcing material. Therefore, FRP bars have received significant attentions and practical application in civil engineering field. However, the thermal stability of FRP bars is poor and so the application of FRP bars is restricted to some extent. Similar to steel reinforced concrete structure, the bond property between FRP bars and concrete is the foundation of their joint work. FRP bars will occur glass transition and thermal decomposition after high temperature, this will create the significant change of the bond property between FRP bars and concrete. Therefore, the study on tensile property of FRP bars and bond behavior between FRP bars and concrete after high temperature is important for the fire-protection of FRP bars reinforced concrete structure. Tensile tests and pull-out tests are performed in this paper, with emphasis on the longitudinal tensile property of FRP bars and the bond behavior between FRP bars and concrete after high temperature. The following several aspects are mainly included:1. Through the tensile tests, longitudinal tensile behavior of BFRP bars and GFRP bars was studied before and after high temperature. Test parameters include temperature, FRP bar diameter, FRP bar type and constant temperature time. The results show that, tensile strength of FRP bars decline gradually as temperature rises. Within the range of test temperature, tensile modules of elasticity are less affected by high temperature. Tensile strength of BFRP bars increase within a small range with the increasing diameters. The smaller diameter of BFRP bars is, the greater drop of tensile strength of BFRP bars is. The diameter of BFRP bars has no obvious influence on modulus of elasticity. The high temperature resistance of BFRP bars is better than that of GFRP bars. At270℃, tensile strength of FRP bars decreases gradually as constant temperature time increases, and decreases greatly in the first half an hour, then decreases slowly. 2. Through the pull-out tests, bond behavior between FRP bars and concrete were studied before and after high temperature. Test parameters include temperature, anchorage length, FRP bar diameter, strength grades of concrete, thickness of concrete cover and fire-retardant coating. The results show that, bond strength between FRP bars and concrete declines gradually as temperature rises. Bond strength between GFRP bars and concrete is greater affected by temperature than that between BFRP bars and concrete. Bond strength between FRP bars and concrete decreases as anchorage length and diameter increases, and which increases as concrete strength and concrete cover thickness increases. After different high temperature, bond strength between BFRP bars and concrete is higher than bond strength between GFRP bars and concrete. Fire-retardant coating has no obvious influence on bond strength between FRP bars and concrete. Without any appropriate protective measures, BFRP bars and GFRP bars are not suitable for reinforcing concrete when the temperature is higher than300℃.3. Tensile strength reduction factor of FRP bars after high temperature was suggested. Based on test results and the existing achievements at home and abroad, new formula for bond strength between FRP bars and concrete at room temperature and after high temperature is proposed. Meanwhile, embedment length formula of FRP bars at room temperature and after high temperature is suggested.4. The existing bond-slip constitutive relation models between FRP bars and concrete at home and abroad are summarized. The ascending branch of bond-slip constitutive relation curve of FRP bars and concrete is simulated with BPE model and CMR model, and model curves are in good agreement with experimental curves. ANSYS finite element software can be used to simulate bond-slip relationship between FRP bar and concrete with enough accuracy.